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  • Continuously reading from a stream in C#?

    - by Damien Wildfire
    I have a Stream object that occasionally gets some data on it, but at unpredictable intervals. Messages that appear on the Stream are well-defined and declare the size of their payload in advance (the size is a 16-bit integer contained in the first two bytes of each message). I'd like to have a StreamWatcher class which detects when the Stream has some data on it. Once it does, I'd like an event to be raised so that a subscribed StreamProcessor instance can process the new message. Can this be done with C# events without using Threads directly? It seems like it should be straightforward, but I can't get quite get my head around the right way to design this.

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  • [Raise|Trigger|Fire|...] an event?!?

    - by winSharp93
    Hello, in a German programming forum we currently have a discussion about events and what you (grammatically) do with them. The MSDN talks about "Event Raising" and "to raise an event". Thus, this seems to be one possibility. Are there any other synonyms? What about "to trigger an event" and "to fire an event"? A Google search will bring results for all of the three possibilities. This, however, does not mean that they are correct, too, of course. Are they? Are there any (stylistic, ...) differences or are they used in different contexts? Many thanks in advance for ending a heated debate :-)

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  • prevent onmouseout when hovering child element of the parent absolute div

    - by John
    Hi I am having trouble with the onmouseout function in a absolute positoned div. When the mouse hits a child element in the div, the mouseout event fires, but I do not want it to fire until the mouse is out of the parent, absolute div. How can I prevent the mouseout event from firing when it hits a child element WITHOUT jquery. I know this has something to do with event bubbling, but I am having no luck on finding out how to work this out. A similar post I found here: How to disable mouseout events triggered by child elements? How ever that solution uses jquery.

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  • Enableeventvalidation in web user control

    - by Khushi
    Hi, i have a web user control containing a repeater. The repeater contains three buttons. On button click it gives the following error : Invalid postback or callback argument. Event validation is enabled using in configuration or <%@ Page EnableEventValidation="true" % in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation. Since user control does not have page directive, so i changed the enableEventValidation to false, but it restricted the itemcommand event of the repeater. Can someone guide me, how to solve this problem?

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  • Trying to import SQL file in a xampp server returns error

    - by Victor_J_Martin
    I have done a ER diagram in Mysql Workbench, and I am trying load in my server with phpMyAdmin, but it returns me the next error: Error SQL Query: -- ----------------------------------------------------- -- Table `BDA`.`UG` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS `BDA`.`UG` ( `numero_ug` INT NOT NULL, `nombre` VARCHAR(45) NOT NULL, `segunda_firma_autorizada` VARCHAR(45) NOT NULL, `fecha_creacion` DATE NOT NULL, `nombre_depto` VARCHAR(140) NOT NULL, `dni` INT NOT NULL, `anho_contable` INT NOT NULL, PRIMARY KEY (`numero_ug`), INDEX `nombre_depto_idx` (`nombre_depto` ASC), INDEX `dni_idx` (`dni` ASC), INDEX `anho_contable_idx` (`anho_contable` ASC), CONSTRAINT `nombre_depto` FOREIGN KEY (`nombre_depto`) REFERENCES `BDA`.`Departamento` (`nombre_depto`) ON DELETE NO ACTION ON UPDATE NO ACTION, CONSTRAINT `dni` FOREIGN KEY (`dni`) REFERENCES `BDA`.`Trabajador` (`dni`) ON DELETE NO ACTION ON UPDATE NO ACTION, CONSTRAINT `anho_contable` FOREIGN KEY (`anho_contable`) REFERENCES `BDA`.`Capitulo_Contable` (`anho_contable`) [...] MySQL said: Documentation #1022 - Can't write; duplicate key in table 'ug' I export the result of the diagram from Mysql Workbench to a SQL file, and this file is what I'm trying to upload. This is the file. I can not find the duplicate key. SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0; SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0; SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='TRADITIONAL,ALLOW_INVALID_DATES'; CREATE SCHEMA IF NOT EXISTS `BDA` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci ; USE `BDA` ; -- ----------------------------------------------------- -- Table `BDA`.`Departamento` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS `BDA`.`Departamento` ( `nombre_depto` VARCHAR(140) NOT NULL, `area_depto` VARCHAR(140) NOT NULL, PRIMARY KEY (`nombre_depto`)) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `BDA`.`Trabajador` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS `BDA`.`Trabajador` ( `dni` INT NOT NULL, `direccion` VARCHAR(140) NOT NULL, `nombre` VARCHAR(45) NOT NULL, `apellidos` VARCHAR(140) NOT NULL, `fecha_nacimiento` DATE NOT NULL, `fecha_contrato` DATE NOT NULL, `titulacion` VARCHAR(140) NULL, `nombre_depto` VARCHAR(45) NOT NULL, PRIMARY KEY (`dni`), INDEX `nombre_depto_idx` (`nombre_depto` ASC), CONSTRAINT `nombre_depto` FOREIGN KEY (`nombre_depto`) REFERENCES `BDA`.`Departamento` (`nombre_depto`) ON DELETE NO ACTION ON UPDATE NO ACTION) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `BDA`.`Capitulo_Contable` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS `BDA`.`Capitulo_Contable` ( `anho_contable` INT NOT NULL, `numero_ug` INT NOT NULL, `debe` DOUBLE NOT NULL, `haber` DOUBLE NOT NULL, PRIMARY KEY (`anho_contable`), INDEX `numero_ug_idx` (`numero_ug` ASC), CONSTRAINT `numero_ug` FOREIGN KEY (`numero_ug`) REFERENCES `BDA`.`UG` (`numero_ug`) ON DELETE NO ACTION ON UPDATE NO ACTION) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `BDA`.`UG` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS `BDA`.`UG` ( `numero_ug` INT NOT NULL, `nombre` VARCHAR(45) NOT NULL, `segunda_firma_autorizada` VARCHAR(45) NOT NULL, `fecha_creacion` DATE NOT NULL, `nombre_depto` VARCHAR(140) NOT NULL, `dni` INT NOT NULL, `anho_contable` INT NOT NULL, PRIMARY KEY (`numero_ug`), INDEX `nombre_depto_idx` (`nombre_depto` ASC), INDEX `dni_idx` (`dni` ASC), INDEX `anho_contable_idx` (`anho_contable` ASC), CONSTRAINT `nombre_depto` FOREIGN KEY (`nombre_depto`) REFERENCES `BDA`.`Departamento` (`nombre_depto`) ON DELETE NO ACTION ON UPDATE NO ACTION, CONSTRAINT `dni` FOREIGN KEY (`dni`) REFERENCES `BDA`.`Trabajador` (`dni`) ON DELETE NO ACTION ON UPDATE NO ACTION, CONSTRAINT `anho_contable` FOREIGN KEY (`anho_contable`) REFERENCES `BDA`.`Capitulo_Contable` (`anho_contable`) ON DELETE NO ACTION ON UPDATE NO ACTION) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `BDA`.`Cliente` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS `BDA`.`Cliente` ( `cif_cliente` INT NOT NULL, `nombre_cliente` VARCHAR(140) NOT NULL, PRIMARY KEY (`cif_cliente`)) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `BDA`.`Ingreso` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS `BDA`.`Ingreso` ( `id` INT NOT NULL, `concepto` VARCHAR(45) NOT NULL, `importe` DOUBLE NOT NULL, `fecha` DATE NOT NULL, `cif_cliente` INT NOT NULL, `numero_ug` INT NOT NULL, PRIMARY KEY (`id`), INDEX `cif_cliente_idx` (`cif_cliente` ASC), INDEX `numero_ug_idx` (`numero_ug` ASC), CONSTRAINT `cif_cliente` FOREIGN KEY (`cif_cliente`) REFERENCES `BDA`.`Cliente` (`cif_cliente`) ON DELETE NO ACTION ON UPDATE NO ACTION, CONSTRAINT `numero_ug` FOREIGN KEY (`numero_ug`) REFERENCES `BDA`.`UG` (`numero_ug`) ON DELETE NO ACTION ON UPDATE NO ACTION) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `BDA`.`Proveedor` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS `BDA`.`Proveedor` ( `cif_proveedor` INT NOT NULL, `nombre_proveedor` VARCHAR(140) NOT NULL, PRIMARY KEY (`cif_proveedor`)) ENGINE = InnoDB; -- ----------------------------------------------------- -- Table `BDA`.`Gasto` -- ----------------------------------------------------- CREATE TABLE IF NOT EXISTS `BDA`.`Gasto` ( `id` INT NOT NULL, `concepto` VARCHAR(45) NOT NULL, `importe` DOUBLE NOT NULL, `fecha` DATE NOT NULL, `factura` INT NOT NULL, `cif_proveedor` INT NOT NULL, `numero_ug` INT NOT NULL, PRIMARY KEY (`id`), INDEX `cif_proveedor_idx` (`cif_proveedor` ASC), INDEX `numero_ug_idx` (`numero_ug` ASC), CONSTRAINT `cif_proveedor` FOREIGN KEY (`cif_proveedor`) REFERENCES `BDA`.`Proveedor` (`cif_proveedor`) ON DELETE NO ACTION ON UPDATE NO ACTION, CONSTRAINT `numero_ug` FOREIGN KEY (`numero_ug`) REFERENCES `BDA`.`UG` (`numero_ug`) ON DELETE NO ACTION ON UPDATE NO ACTION) ENGINE = InnoDB; SET SQL_MODE=@OLD_SQL_MODE; SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS; SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS; Thanks for your advices.

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  • Self-updating collection concurrency issues

    - by DEHAAS
    I am trying to build a self-updating collection. Each item in the collection has a position (x,y). When the position is changed, an event is fired, and the collection will relocate the item. Internally the collection is using a “jagged dictionary”. The outer dictionary uses the x-coordinate a key, while the nested dictionary uses the y-coordinate a key. The nested dictionary then has a list of items as value. The collection also maintains a dictionary to store the items position as stored in the nested dictionaries – item to stored location lookup. I am having some trouble making the collection thread safe, which I really need. Source code for the collection: public class PositionCollection<TItem, TCoordinate> : ICollection<TItem> where TItem : IPositionable<TCoordinate> where TCoordinate : struct, IConvertible { private readonly object itemsLock = new object(); private readonly Dictionary<TCoordinate, Dictionary<TCoordinate, List<TItem>>> items; private readonly Dictionary<TItem, Vector<TCoordinate>> storedPositionLookup; public PositionCollection() { this.items = new Dictionary<TCoordinate, Dictionary<TCoordinate, List<TItem>>>(); this.storedPositionLookup = new Dictionary<TItem, Vector<TCoordinate>>(); } public void Add(TItem item) { if (item.Position == null) { throw new ArgumentException("Item must have a valid position."); } lock (this.itemsLock) { if (!this.items.ContainsKey(item.Position.X)) { this.items.Add(item.Position.X, new Dictionary<TCoordinate, List<TItem>>()); } Dictionary<TCoordinate, List<TItem>> xRow = this.items[item.Position.X]; if (!xRow.ContainsKey(item.Position.Y)) { xRow.Add(item.Position.Y, new List<TItem>()); } xRow[item.Position.Y].Add(item); if (this.storedPositionLookup.ContainsKey(item)) { this.storedPositionLookup[item] = new Vector<TCoordinate>(item.Position); } else { this.storedPositionLookup.Add(item, new Vector<TCoordinate>(item.Position)); // Store a copy of the original position } item.Position.PropertyChanged += (object sender, PropertyChangedEventArgs eventArgs) => this.UpdatePosition(item, eventArgs.PropertyName); } } private void UpdatePosition(TItem item, string propertyName) { lock (this.itemsLock) { Vector<TCoordinate> storedPosition = this.storedPositionLookup[item]; this.RemoveAt(storedPosition, item); this.storedPositionLookup.Remove(item); } } } I have written a simple unit test to check for concurrency issues: [TestMethod] public void TestThreadedPositionChange() { PositionCollection<Crate, int> collection = new PositionCollection<Crate, int>(); Crate crate = new Crate(new Vector<int>(5, 5)); collection.Add(crate); Parallel.For(0, 100, new Action<int>((i) => crate.Position.X += 1)); Crate same = collection[105, 5].First(); Assert.AreEqual(crate, same); } The actual stored position varies every time I run the test. I appreciate any feedback you may have.

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  • How can I decrypt encrypted files using a PEM private key?

    - by Phil Cole
    I have files which have either been encrypted with a public key and the Blowfish algorithm, or a public key and the AES-256 algorithm. I'm looking to put together a Perl script that would be able to use the private keys (which I do have) to decrypt the files. The public and private key files are all in PEM format, and while I can find ways of reading the PEM files, and ways of decrypting data with a key, I haven't yet found a way of going from PEM - key. Any suggestions?

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  • How to retrieve from two tables with same foreign key repeated more than once?

    - by Sarenya
    How to display the data of tables that are linked by a primary key and foreign key where the foreign key of the data repeats? For ex. I have two tables, ParentTable and Childtable. The primary key of ParentTable acts as the foreign key of ChildTable. There are more than one record with same ParentId in ChildTable. How to retrieve them and display in a single Grid or List or any type of view?

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  • Windows 7 Activation: Can I use OEM key for retail version? [closed]

    - by Joudicek Jouda
    Possible Duplicate: Windows 7 and Vista Activation FAQ: How do language, version, 64-bit or 32-bit, and source affect ability to install and transfer Windows licenses? I have a Lenovo notebook with pre-installed Windows 7 Professional x64. I just did a clean reinstall with retail installation Win7 Professional x64 disk I got from MSDNAA programme I'm member. I wanted to install the OS as Lenovo OEM with the same key I had before, but when I tried to activate the newly installed Windows, it gave me 0xc004e003 error. So the question is, can I use my OEM key for Win7 installed as retail? If not, can I somehow change the installed OS to OEM? The other think is, the OEM key I have tried is just some key I found in my notes, because I don't have any Windows sticker on beneath my laptop as it used to be on all my previous ones. Can I somehow find out "what is the origin" of the supposed key I'm trying to use?

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  • Cannot open simple script application on mac

    - by streetpc
    Mac OS X 10.6 I created a very simple app, which is only a wrapper of a shell script (so that I can select this script in application selectors, like startup apps). I try to launch it and yesterday it worked, but today I changed the executable script's content and name (with something that perfeclty works in a shell script launched in the Terminal) and it will only display a Finder-iconed dialog saying Cannot open the application because it is not supported on this kind of Mac. I restored the previous script (content/name) but I still get the error! Same when re-bundling the app from scratch, or completely changing the bundle identifier… If I try to open it in the Terminal using open My.app, I get The application cannot be opened because it has an incorrect executable format. But when I executes directly the Contents/MacOS/Script, it allways works (iwth both contents). Also, it is displayed with correct icon and meta-information in the Finder (so I guess the Info.plist is understood). The app's file tree is: Contents/ Info.plist MacOS/ Script (executable bit set, works when launched directly) PkgInfo Resources/ AppIcon.icns Here is the Info.plist content: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>CFBundleExecutable</key> <string>Script</string> <key>CFBundleIconFile</key> <string>AppIcon</string> <key>CFBundleIdentifier</key> <string>asdf.ScriptApp</string> <key>CFBundleInfoDictionaryVersion</key> <string>6.0</string> <key>CFBundleName</key> <string>My script</string> <key>CFBundlePackageType</key> <string>APPL</string> <key>CFBundleShortVersionString</key> <string>1.0</string> <key>CFBundleSignature</key> <string>????</string> <key>CFBundleVersion</key> <string>1</string> <key>LSMinimumSystemVersion</key> <string>10.4</string> </dict> </plist> And the PkgInfo file only contains APPL????. I tested the Script with a simple echo "ok" and echo "ok" >/tmp/test (plus #!/bin/sh header). So my questions are: Is there some kind of validity caching for applications ? based on what ? how do I flush it ? Where does this message come from ? I tried to google it but all I get is a page talking about 32/64 bits Java…

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  • How do you map a solo press of a modifier key to its own function or mapping on Windows?

    - by Conrad.Dean
    Today on hacker news there was a clever article on custom shortcut keys. The author talks about a technique for remapping a modifier key such as CTRL to ESC if CTRL were pressed without a modifier. This is useful in vim because of how often you need to press ESC. Another technique he describes is mapping the open parenthesis, ( to the left shift key, and ) to the right shift key. If another key is pressed when shift is held down, the shift key behaves normally. The author describes the software he uses on OSX, but is there a way to do this on Windows? I've heard of AutoHotKey but it seems to only fire macros when simple keys are pressed, rather than the conditional state switch that this would require.

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  • Cannot open simplest mac application

    - by streetpc
    I created a very simple app, which is only a wrapper of a shell script (so that I can select this script in application selectors, like startup apps). I try to launch it and yesterday it worked, but today I changed the executable script's content and name (with something that perfeclty works in a shell script launched in the Terminal) and it will only display a Finder-iconed dialog saying Cannot open the application because it is not supported on this kind of Mac. I restored the previous script (content/name) but I still get the error! Same when re-bundling the app from scratch, or completely changing the bundle identifier… If I try to open it in the Terminal using open My.app, I get The application cannot be opened because it has an incorrect executable format. But when I executes directly the Contents/MacOS/Script, it allways works (iwth both contents). Also, it is displayed with correct icon and meta-information in the Finder (so I guess the Info.plist is understood). The app's file tree is: Contents/ Info.plist MacOS/ Script (executable bit set, works when launched directly) PkgInfo Resources/ AppIcon.icns Here is the Info.plist content: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>CFBundleExecutable</key> <string>Script</string> <key>CFBundleIconFile</key> <string>AppIcon</string> <key>CFBundleIdentifier</key> <string>asdf.ScriptApp</string> <key>CFBundleInfoDictionaryVersion</key> <string>6.0</string> <key>CFBundleName</key> <string>My script</string> <key>CFBundlePackageType</key> <string>APPL</string> <key>CFBundleShortVersionString</key> <string>1.0</string> <key>CFBundleSignature</key> <string>????</string> <key>CFBundleVersion</key> <string>1</string> <key>LSMinimumSystemVersion</key> <string>10.4</string> </dict> </plist> And the PkgInfo file only contains APPL????. I tested the Script with a simple echo "ok" and echo "ok" >/tmp/test (plus #!/bin/sh header). So my questions are: * Is there some kind of validity caching for applications ? based on what ? how do I flush it ? * Where does this message come from ? I tried to google it but all I get is a page talking about 32/64 bits Java…

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  • Cannot open simplest script mac application

    - by streetpc
    I created a very simple app, which is only a wrapper of a shell script (so that I can select this script in application selectors, like startup apps). I try to launch it and yesterday it worked, but today I changed the executable script's content and name (with something that perfeclty works in a shell script launched in the Terminal) and it will only display a Finder-iconed dialog saying Cannot open the application because it is not supported on this kind of Mac. I restored the previous script (content/name) but I still get the error! Same when re-bundling the app from scratch, or completely changing the bundle identifier… If I try to open it in the Terminal using open My.app, I get The application cannot be opened because it has an incorrect executable format. But when I executes directly the Contents/MacOS/Script, it allways works (iwth both contents). Also, it is displayed with correct icon and meta-information in the Finder (so I guess the Info.plist is understood). The app's file tree is: Contents/ Info.plist MacOS/ Script (executable bit set, works when launched directly) PkgInfo Resources/ AppIcon.icns Here is the Info.plist content: <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>CFBundleExecutable</key> <string>Script</string> <key>CFBundleIconFile</key> <string>AppIcon</string> <key>CFBundleIdentifier</key> <string>asdf.ScriptApp</string> <key>CFBundleInfoDictionaryVersion</key> <string>6.0</string> <key>CFBundleName</key> <string>My script</string> <key>CFBundlePackageType</key> <string>APPL</string> <key>CFBundleShortVersionString</key> <string>1.0</string> <key>CFBundleSignature</key> <string>????</string> <key>CFBundleVersion</key> <string>1</string> <key>LSMinimumSystemVersion</key> <string>10.4</string> </dict> </plist> And the PkgInfo file only contains APPL????. I tested the Script with a simple echo "ok" and echo "ok" >/tmp/test (plus #!/bin/sh header). So my questions are: Is there some kind of validity caching for applications ? based on what ? how do I flush it ? Where does this message come from ? I tried to google it but all I get is a page talking about 32/64 bits Java…

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  • Can I re-attach SSH key forwarding through a disconnected Screen session?

    - by David Mackintosh
    I have a laptop on which I have pageant (the PuTTy SSH key agent) running. If I ssh to a system and launch screen, the ssh key forwarding works properly. However, if I disconnect from that screen session, log off, then later reconnect -- the key forwarding doesn't work any more. I am presuming that this is because when I reconnect the key forwarding is set up on different ports for the new ssh session than was the old one. Is there a way to teach an individual screen window to reconnect to the agent forwarding so that I can use my key to forward again?

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  • How can one create a bootable linux usb key that works on Mac (Intel 64 bit CPU) hardware ?

    - by user3621
    Hi, I'm trying to create a bootable usb key with linux (debian) and that can be booted on Macintel hardware. I have read that MAC's EFI can only boot GPT GUID formatted disks. I'm desperately trying to find a good tutorial which explains how to create such a key. Here what I have done so far: create a GUID partition on te key using linux GNU parted create a HFS+ or ext3 partition on the key, with the boot flag on install a linux .iso with unetbootin While all steps were successfull and in some cases I could even boot on a PC, the step of booting on Macintel software failed (on a macbook). I need to precise that I holded the "alt" key while booting the mac and the only visible bootable disk was the hard disk. Thanks for any advice. PS: I have tried with rEFIt as well. In one case I had a "windows" icon but it then failed to boot with a message like "no system found"

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  • Why does select SCOPE_IDENTITY() return a decimal instead of an integer?

    - by Earlz
    So I have a table with an identity column as the primary key, so it is an integer. So, why does SCOPE_IDENTITY() always return a decimal value instead of an int to my C# application? This is really annoying since decimal values will not implicitly convert to integers in C#, which means I now have to rewrite a bunch of stuff and have a lot of helper methods because I use SQL Server and Postgres, which Postgres does return an integer for the equivalent function.. Why does SCOPE_IDENTITY() not just return a plain integer? Are there people out there that commonly use decimal/non-identity values for primary keys?

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  • C#/.NET Little Wonders: The EventHandler and EventHandler&lt;TEventArgs&gt; delegates

    - by James Michael Hare
    Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. In the last two weeks, we examined the Action family of delegates (and delegates in general), and the Func family of delegates and how they can be used to support generic, reusable algorithms and classes. So this week, we are going to look at a handy pair of delegates that can be used to eliminate the need for defining custom delegates when creating events: the EventHandler and EventHandler<TEventArgs> delegates. Events and delegates Before we begin, let’s quickly consider events in .NET.  According to the MSDN: An event in C# is a way for a class to provide notifications to clients of that class when some interesting thing happens to an object. So, basically, you can create an event in a type so that users of that type can subscribe to notifications of things of interest.  How is this different than some of the delegate programming that we talked about in the last two weeks?  Well, you can think of an event as a special access modifier on a delegate.  Some differences between the two are: Events are a special access case of delegates They behave much like delegates instances inside the type they are declared in, but outside of that type they can only be (un)subscribed to. Events can specify add/remove behavior explicitly If you want to do additional work when someone subscribes or unsubscribes to an event, you can specify the add and remove actions explicitly. Events have access modifiers, but these only specify the access level of those who can (un)subscribe A public event, for example, means anyone can (un)subscribe, but it does not mean that anyone can raise (invoke) the event directly.  Events can only be raised by the type that contains them In contrast, if a delegate is visible, it can be invoked outside of the object (not even in a sub-class!). Events tend to be for notifications only, and should be treated as optional Semantically speaking, events typically don’t perform work on the the class directly, but tend to just notify subscribers when something of note occurs. My basic rule-of-thumb is that if you are just wanting to notify any listeners (who may or may not care) that something has happened, use an event.  However, if you want the caller to provide some function to perform to direct the class about how it should perform work, make it a delegate. Declaring events using custom delegates To declare an event in a type, we simply use the event keyword and specify its delegate type.  For example, let’s say you wanted to create a new TimeOfDayTimer that triggers at a given time of the day (as opposed to on an interval).  We could write something like this: 1: public delegate void TimeOfDayHandler(object source, ElapsedEventArgs e); 2:  3: // A timer that will fire at time of day each day. 4: public class TimeOfDayTimer : IDisposable 5: { 6: // Event that is triggered at time of day. 7: public event TimeOfDayHandler Elapsed; 8:  9: // ... 10: } The first thing to note is that the event is a delegate type, which tells us what types of methods may subscribe to it.  The second thing to note is the signature of the event handler delegate, according to the MSDN: The standard signature of an event handler delegate defines a method that does not return a value, whose first parameter is of type Object and refers to the instance that raises the event, and whose second parameter is derived from type EventArgs and holds the event data. If the event does not generate event data, the second parameter is simply an instance of EventArgs. Otherwise, the second parameter is a custom type derived from EventArgs and supplies any fields or properties needed to hold the event data. So, in a nutshell, the event handler delegates should return void and take two parameters: An object reference to the object that raised the event. An EventArgs (or a subclass of EventArgs) reference to event specific information. Even if your event has no additional information to provide, you are still expected to provide an EventArgs instance.  In this case, feel free to pass the EventArgs.Empty singleton instead of creating new instances of EventArgs (to avoid generating unneeded memory garbage). The EventHandler delegate Because many events have no additional information to pass, and thus do not require custom EventArgs, the signature of the delegates for subscribing to these events is typically: 1: // always takes an object and an EventArgs reference 2: public delegate void EventHandler(object sender, EventArgs e) It would be insane to recreate this delegate for every class that had a basic event with no additional event data, so there already exists a delegate for you called EventHandler that has this very definition!  Feel free to use it to define any events which supply no additional event information: 1: public class Cache 2: { 3: // event that is raised whenever the cache performs a cleanup 4: public event EventHandler OnCleanup; 5:  6: // ... 7: } This will handle any event with the standard EventArgs (no additional information).  But what of events that do need to supply additional information?  Does that mean we’re out of luck for subclasses of EventArgs?  That’s where the generic for of EventHandler comes into play… The generic EventHandler<TEventArgs> delegate Starting with the introduction of generics in .NET 2.0, we have a generic delegate called EventHandler<TEventArgs>.  Its signature is as follows: 1: public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e) 2: where TEventArgs : EventArgs This is similar to EventHandler except it has been made generic to support the more general case.  Thus, it will work for any delegate where the first argument is an object (the sender) and the second argument is a class derived from EventArgs (the event data). For example, let’s say we wanted to create a message receiver, and we wanted it to have a few events such as OnConnected that will tell us when a connection is established (probably with no additional information) and OnMessageReceived that will tell us when a new message arrives (probably with a string for the new message text). So for OnMessageReceived, our MessageReceivedEventArgs might look like this: 1: public sealed class MessageReceivedEventArgs : EventArgs 2: { 3: public string Message { get; set; } 4: } And since OnConnected needs no event argument type defined, our class might look something like this: 1: public class MessageReceiver 2: { 3: // event that is called when the receiver connects with sender 4: public event EventHandler OnConnected; 5:  6: // event that is called when a new message is received. 7: public event EventHandler<MessageReceivedEventArgs> OnMessageReceived; 8:  9: // ... 10: } Notice, nowhere did we have to define a delegate to fit our event definition, the EventHandler and generic EventHandler<TEventArgs> delegates fit almost anything we’d need to do with events. Sidebar: Thread-safety and raising an event When the time comes to raise an event, we should always check to make sure there are subscribers, and then only raise the event if anyone is subscribed.  This is important because if no one is subscribed to the event, then the instance will be null and we will get a NullReferenceException if we attempt to raise the event. 1: // This protects against NullReferenceException... or does it? 2: if (OnMessageReceived != null) 3: { 4: OnMessageReceived(this, new MessageReceivedEventArgs(aMessage)); 5: } The above code seems to handle the null reference if no one is subscribed, but there’s a problem if this is being used in multi-threaded environments.  For example, assume we have thread A which is about to raise the event, and it checks and clears the null check and is about to raise the event.  However, before it can do that thread B unsubscribes to the event, which sets the delegate to null.  Now, when thread A attempts to raise the event, this causes the NullReferenceException that we were hoping to avoid! To counter this, the simplest best-practice method is to copy the event (just a multicast delegate) to a temporary local variable just before we raise it.  Since we are inside the class where this event is being raised, we can copy it to a local variable like this, and it will protect us from multi-threading since multicast delegates are immutable and assignments are atomic: 1: // always make copy of the event multi-cast delegate before checking 2: // for null to avoid race-condition between the null-check and raising it. 3: var handler = OnMessageReceived; 4: 5: if (handler != null) 6: { 7: handler(this, new MessageReceivedEventArgs(aMessage)); 8: } The very slight trade-off is that it’s possible a class may get an event after it unsubscribes in a multi-threaded environment, but this is a small risk and classes should be prepared for this possibility anyway.  For a more detailed discussion on this, check out this excellent Eric Lippert blog post on Events and Races. Summary Generic delegates give us a lot of power to make generic algorithms and classes, and the EventHandler delegate family gives us the flexibility to create events easily, without needing to redefine delegates over and over.  Use them whenever you need to define events with or without specialized EventArgs.   Tweet Technorati Tags: .NET, C#, CSharp, Little Wonders, Generics, Delegates, EventHandler

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  • How to call postback using javascript on ASP.NET form

    - by Anton
    I have a web form with textbox and button. I want after "ENTER" key click on textbox postbak form. I am using next code: onkeypress=" if(event.keyCode==13) { alert(2); WebForm_DoPostBackWithOptions(new WebForm_PostBackOptions('ctl00$ContentPlaceHolder1$btnSearch', '', true, '', '', false, false)); alert(2); return false;} where WebForm_DoPostBackWithOptions(new WebForm_PostBackOptions('ctl00$ContentPlaceHolder1$btnSearch', '', true, '', '', false, false)); is javascript code for button event onclick. I get two alerts, but postback doesnot happen. Any ideas what is wrong?

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  • Need strategy to phone home to a Pyton web app and check licensing information for a commercial Wind

    - by Cornish
    What's a good strategy for building licensing checking into a Windows desktop app using a Python web application? This is a very open ended question because I don't have the slightest clue how to start to build this feature. What I do have is a number of general concerns: I have developed a commercial Windows desktop application and I want to make money from it but I don't want to build the licensing into the app since it's inevitable that someone will create a keygen or a crack, circulate it online and then it's 'game over' for me. So my idea was to create a web application where people could purchase a license key that is generated by the web app and every time the desktop application is started up, it will 'phone home' to the web app to check whether the license is valid and whether it seems to be in use at multiple locations. I'm just not sure how to do this. Would appreciate any general technical strategies and/or pointers to libraries/modules that might be of use.

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  • Analytics: Test events not showing up - how to troubleshoot?

    - by David Parks
    I've got 3 profiles: Master, Raw Data, and Test, on the Test profile I have no filters configured. I want to test using some events. I created a local HTML file as shown below to generate some test data that I could play with in Analytics. But the events never showed up in Analytics. I wonder what I might be doing wrong? Is the lack of a domain an issue maybe? <html><head></head><body>Login_popup_complete_Facebook <script type="text/javascript"> var _gaq = _gaq || []; _gaq.push(['_setAccount', 'UA-28554309-1']); _gaq.push(['_trackPageview']); _gaq.push(['_trackEvent', 'Login popup completed', 'Facebook']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); </script> </body></html>

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  • What one-time-password devices are compatible with mod_authn_otp?

    - by netvope
    mod_authn_otp is an Apache web server module for two-factor authentication using one-time passwords (OTP) generated via the HOTP/OATH algorithm defined in RFC 4226. The developer's has listed only one compatible device (the Authenex's A-Key 3600) on their website. If a device is fully compliant with the standard, and it allows you to recover the token ID, it should work. However, without testing, it's hard to tell whether a device is fully compliant. Have you ever tried other devices (software or hardware) with mod_authn_otp (or other open source server-side OTP program)? If yes, please share your experience :)

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  • Is there any legitimate use for bare strings in PHP?

    - by Robert
    This question got me thinking about bare strings. When PHP sees a string that's not enclosed in quotes, it first checks to see if it's a constant. If not, it just assumes it's a string and goes on anyway. So for example if I have echo $foo[bar]; If there's a constant called bar it uses that for the array key, but if not then it treats bar as a bare string, so it behaves just like echo $foo["bar"]; This can cause all kinds of problems if at some future date a constant is added with the same name. My question is, is there any situation in which it actually makes sense to use a bare string?

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  • Choice of primary index for mysql innoDB

    - by Saif Bechan
    I have an auction website where users can place a bid on a product. Now i have a primary index on the bid table for easy access of the last places bid on the product. This index is just a unique auto incrementing value. During the week this number becomes huge!! I was wondering if this is a good setup for the primary key in an innoDB table. The bids table exist of the following important fields: table: bids fields: user_id,product_id,bid So what i want to do is make the primary of these 3 fields combined. Is this a good idea or is this just too much for innoDB keys.

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  • Access event.target in IE8 unobstrusive Javascript

    - by Mirko
    The following function gets the target element in a dropdown menu: function getTarget(evt){ var targetElement = null; //if it is a standard browser if (typeof evt.target != 'undefined'){ targetElement = evt.target; } //otherwise it is IE then adapt syntax else{ targetElement = evt.srcElement; } //return id of element when hovering over or if (targetElement.nodeName.toLowerCase() == 'li'){ return targetElement; } else if (targetElement.parentNode.nodeName.toLowerCase() == 'li'){ return targetElement.parentNode; } else{ return targetElement; } Needless to say, it works in Firefox, Chrome, Safari and Opera but it does not in IE8 (and I guess in previous versions as well). When I try to debug it with IE8 I get the error "Member not Found" on the line: targetElement = evt.srcElement; along with other subsequent errors, but I think this is the key line. Any help will be appreciated.

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  • Loading Fact Table + Lookup / UnionAll for SK lookups.

    - by Nev_Rahd
    I got to populate FactTable with 12 lookups to dimension table to get SK's, of which 6 are to different Dim Tables and rest 6 are lookup to same DimTable (type II) doing lookup to same natural key. Ex: PrimeObjectID = lookup to DimObject.ObjectID = get ObjectSK and got other columns which does same OtherObjectID1 = lookup to DimObject.ObjectID = get ObjectSK OtherObjectID2 = lookup to DimObject.ObjectID = get ObjectSK OtherObjectID3 = lookup to DimObject.ObjectID = get ObjectSK OtherObjectID4 = lookup to DimObject.ObjectID = get ObjectSK OtherObjectID5 = lookup to DimObject.ObjectID = get ObjectSK for such multiple lookup how should go in my SSIS package. for now am using lookup / unionall foreach lookup. Is there a better way to this.

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