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  • Strategy for animating a lot of "LED's" - thread?, UIView animations? NSOperation? (iPhone)

    - by RickiG
    Hi I have to do some different views containing 72 LED lights. I built an LED Class so I can loop through the LED's and set them to different colors (Green, Red, Orange, Blue None etc.). The LED then loads the appropriate .png. This works fine, I loop over the LED's and set them. Now I know that at some time they will need to not just turn on/off change color, but will have to turn on with a small delay. Like an equalizer. I have a 5-10 views containing the 72 LED's and I would like to achieve the above with the minimum amount of memory/CPU strain. for(LED *l in self.ledArray) { [l display:Green]; } I simply loop as shown above and inside the LED is a switch case that does the correct logic. If this were actual LED's and a microController I would use sleep(100) or similar in the loop, but I would really like to avoid stuff like that for obvious reasons. I was thinking that doing a performOnThread withDelay would really be consuming, so would UIView animation changing the alpha and NSOperation would also be a lot of lifting for a small feature. Is there a both efficient and clever way to go around this? Thanks for any inspiration given:)

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  • Version Control: multiple version hell, file synchronization

    - by SigTerm
    Hello. I would like to know how you normally deal with this situation: I have a set of utility functions. Say..5..10 files. And technically they are static library, cross-platform - SConscript/SConstruct plus Visual Studio project (not solution). Those utility functions are used in multiple small projects (15+, number increases over time). Each project has a copy of a few files or of an entire library, not a link into one central place. Sometimes project uses one file, two files, some use everything. Normally, utility functions are included as a copy of every file and SConscript/SConstruct or Visual Studio Project (depending on the situation). Each project has a separate git repository. Sometimes one project is derived from other, sometimes it isn't. You work on every one of them, in random order. There are no other people (to make things simpler) The problem arises when while working on one project you modify those utility function files. Because each project has a copy of file, this introduces new version, which leads to the mess when you try later (week later, for example) to guess which version has a most complete functionality (i.e. you added a function to a.cpp in one project, and added another function to a.cpp in another project, which created a version fork) How would you handle this situation to avoid "version hell"? One way I can think of is using symbolic links/hard links, but it isn't perfect - if you delete one central storage, it will all go to hell. And hard links won't work on dual-boot system (although symbolic links will). It looks like what I need is something like advanced git repository, where code for the project is stored in one local repository, but is synchronized with multiple external repositories. But I'm not sure how to do it or if it is possible to do this with git. So, what do you think?

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  • Android - Temporal & Ancestral Navigation with ViewPager & Fragments

    - by rascuache
    I'm trying to work out the best way to implement the 'ancestral' and 'temporal' navigation (utilising the up button and back buttons), for a music player I'm working on. Currently, the user is presented with a viewpager, and can page between three main fragments (ArtistMain, AlbumMain and SongMain). Upon choosing an item inside that view, a fragment transaction occurs, and the viewpager goes out of view, replaced by a new fragment (AlbumSub, Songsub or player, depending on where the user came from). The user can then navigate deeper, until a song is chosen, and then they are taken to the 'player' screen. I guess the question is: How do I implement all of this conditional navigation? I'm fairly new to android and programming in general, and I just can't seem to come up with an efficient way to achieve this. At the moment, as each fragment is brought into view, the app is checking to see where the user just came from, and then determines where the user should be taken if back or home is called. This means I have a booleans like "fromArtistMain", "fromAlbumSub", and I'm checking for things like "fromSongSub && fromPlayer".. it's all turning into a bit of a mess. I've drawn a diagram (in paint, sorry!!), to depict the navigation I'm trying to achieve. The yellow represents the 'up' button press, the red is the 'back' button press, and blue is just normal navigation. The green arrows are meant to represent the view paging: Any advice is welcome. It might take something really simple that I've just overlooked. Thanks for your time.

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  • Where should I put contextual data related to an Object that is not really a property of the object?

    - by RenderIn
    I have a Car class. It has three properties: id, color and model. In a particular query I want to return all the cars and their properties, and I also want to return a true/false field called "searcherKnowsOwner" which is a field I calculate in my database query based on whether or not the individual conducting the search knows the owner. I have a database function that takes the ID of the searcher and the ID of the car and returns a boolean. My car class looks like this (pseudocode): class Car{ int id; Color color; Model model; } I have a screen where I want to display all the cars, but I also want to display a flag next to each car if the person viewing the page knows the owner of that car. Should I add a field to the Car class, a boolean searcherKnowsOwner? It's not a property of the car, but is actually a property of the user conducting the search. But this seems like the most efficient place to put this information.

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  • Select all points in a matrix within 30m of another point

    - by pinnacler
    So if you look at my other posts, it's no surprise I'm building a robot that can collect data in a forest, and stick it on a map. We have algorithms that can detect tree centers and trunk diameters and can stick them on a cartesian XY plane. We're planning to use certain 'key' trees as natural landmarks for localizing the robot, using triangulation and trilateration among other methods, but programming this and keeping data straight and efficient is getting difficult using just Matlab. Is there a technique for sub-setting an array or matrix of points? Say I have 1000 trees stored over 1km (1000m), is there a way to say, select only points within 30m radius of my current location and work only with those? I would just use a GIS, but I'm doing this in Matlab and I'm unaware of any GIS plugins for Matlab. I forgot to mention, this code is going online, meaning it's going on a robot for real-time execution. I don't know if, as the map grows to several miles, using a different data structure will help or if calculating every distance to a random point is what a spatial database is going to do anyway. I'm thinking of mirroring two arrays, one sorted by X and the other by Y. Then bubble sorting to determine the 30m range in that. I do the same for both arrays, X and Y, and then have a third cross link table that will select the individual values. But I don't know, what that's called, how to program that and I'm sure someone already has so I don't want to reinvent the wheel. Cartesian Plane GIS

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  • Moving inserted container element if possible

    - by doublep
    I'm trying to achieve the following optimization in my container library: when inserting an lvalue-referenced element, copy it to internal storage; but when inserting rvalue-referenced element, move it if supported. The optimization is supposed to be useful e.g. if contained element type is something like std::vector, where moving if possible would give substantial speedup. However, so far I was unable to devise any working scheme for this. My container is quite complicated, so I can't just duplicate insert() code several times: it is large. I want to keep all "real" code in some inner helper, say do_insert() (may be templated) and various insert()-like functions would just call that with different arguments. My best bet code for this (a prototype, of course, without doing anything real): #include <iostream> #include <utility> struct element { element () { }; element (element&&) { std::cerr << "moving\n"; } }; struct container { void insert (const element& value) { do_insert (value); } void insert (element&& value) { do_insert (std::move (value)); } private: template <typename Arg> void do_insert (Arg arg) { element x (arg); } }; int main () { { // Shouldn't move. container c; element x; c.insert (x); } { // Should move. container c; c.insert (element ()); } } However, this doesn't work at least with GCC 4.4 and 4.5: it never prints "moving" on stderr. Or is what I want impossible to achieve and that's why emplace()-like functions exist in the first place?

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  • Using the contents of an array to set individual pixels in a Quartz bitmap context

    - by Magic Bullet Dave
    I have an array that contains the RGB colour values for each pixel in a 320 x 180 display. I would like to be able to set individual pixel values in the a bitmap context of the same size offscreen then display the bitmap context in a view. It appears that I have to create 1x1 rects and either put a stroke on them or a line of length 1 at the point in question. Is that correct? I'm looking for a very efficient way of getting the array data onto the graphics context as you can imagine this is going to be an image buffer that cycles at 25 frames per second and drawing in this way seems inefficient. I guess the other question is should I use OPENGL ES instead? Thoughts/best practice would be much appreciated. Regards Dave OK, have come a short way, but can't make the final hurdle and I am not sure why this isn't working: - (void) displayContentsOfArray1UsingBitmap: (CGContextRef)context { long bitmapData[WIDTH * HEIGHT]; // Build bitmap int i, j, h; for (i = 0; i < WIDTH; i++) { for (j = 0; j < HEIGHT; j++) { h = frameBuffer01[i][j]; bitmapData[i * j] = h; } } // Blit the bitmap to the context CGDataProviderRef providerRef = CGDataProviderCreateWithData(NULL, bitmapData,4 * WIDTH * HEIGHT, NULL); CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB(); CGImageRef imageRef = CGImageCreate(WIDTH, HEIGHT, 8, 32, WIDTH * 4, colorSpaceRef, kCGImageAlphaFirst, providerRef, NULL, YES, kCGRenderingIntentDefault); CGContextDrawImage(context, CGRectMake(0.0, HEIGHT, WIDTH, HEIGHT), imageRef); CGImageRelease(imageRef); CGColorSpaceRelease(colorSpaceRef); CGDataProviderRelease(providerRef); }

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  • Simplest distributed persistent key/value store that supports primary key range queries

    - by StaxMan
    I am looking for a properly distributed (i.e. not just sharded) and persisted (not bounded by available memory on single node, or cluster of nodes) key/value ("nosql") store that does support range queries by primary key. So far closest such system is Cassandra, which does above. However, it adds support for other features that are not essential for me. So while I like it (and will consider using it of course), I am trying to figure out if there might be other mature projects that implement what I need. Specifically, for me the only aspect of value I need is to access it as a blob. For key, however, I need range queries (as in, access values ordered, limited by start and/or end values). While values can have structures, there is no need to use that structure for anything on server side (can do client-side data binding, flexible value/content types etc). For added bonus, Cassandra style storage (journaled, all sequential writes) seems quite optimal for my use case. To help filter out answers, I have investigated some alternatives within general domain like: Voldemort (key/value, but no ordering) and CouchDB (just sharded, more batch-oriented); and am aware of systems that are not quite distributed while otherwise qualifying (bdb variants, tokyo cabinet itself (not sure if Tyrant might qualify), redis (in-memory store only)).

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  • What's the best way to retrieve two pieces of data from an XML file?

    - by Morinar
    I've got an XML document that is in either a pre or post FO transformed state that I need to extract some information from. In the pre-case, I need to pull out two tags that represent the pageWidth and pageHeight and in the post case I need to extract the page-height and page-width parameters from a specific tag (I forget which one it is off the top of my head). What I'm looking for is an efficient/easily maintainable way to grab these two elements. I'd like to only read the document a single time fetching the two things I need. I initially started writing something that would use BufferedReader + FileReader, but then I'm doing string searching and it gets messy when the tags span multiple lines. I then looked at the DOMParser, which seems like it would be ideal, but I don't want to have to read the entire file into memory if I could help it as the files could potentially be large and the tags I'm looking for will nearly always be close to the top of the file. I then looked into SAXParser, but that seems like a big pile of complicated overkill for what I'm trying to accomplish. Anybody have any advice? Or simple implementations that would accomplish my goal? Thanks.

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  • Basic Contact Form in PHP

    - by NessDan
    I'm working on a contact form for my church website. The church has an email already registered (it's POP3) and the hosting company says their mail server is mymail.brinkster.com . With all that information, how can you send the form using mail()? The server won't show PHP errors. The current code looks like this: $headers = 'MIME-Version: 1.0' . "\r\n"; $headers .= 'Content-type: text/html; charset=iso-8859-1' . "\r\n"; $headers .= 'From: *ChurchsEmail*' . "\r\n"; if(mail("*MyEmailHere*", "Setting Up PHP Email", "This would be the body of the email.", $headers)) { echo "The email was successfully sent."; } else { echo "The email was NOT sent."; } All I get back is "The email was NOT sent." So does anyone have any experience setting up an email form like this? My thanks to anyone who can help me out and any efficient ways of doing this, let me know!

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  • How to replace characters in a java String?

    - by ManBugra
    I like to replace a certain set of characters of a string with a corresponding replacement character in an efficent way. For example: String sourceCharacters = "šdccŠÐCCžŽ"; String targetCharacters = "sdccSDCCzZ"; String result = replaceChars("Gracišce", sourceCharacters , targetCharacters ); Assert.equals(result,"Gracisce") == true; Is there are more efficient way than to use the replaceAll method of the String class? My first idea was: final String s = "Gracišce"; String sourceCharacters = "šdccŠÐCCžŽ"; String targetCharacters = "sdccSDCCzZ"; // preparation final char[] sourceString = s.toCharArray(); final char result[] = new char[sourceString.length]; final char[] targetCharactersArray = targetCharacters.toCharArray(); // main work for(int i=0,l=sourceString.length;i<l;++i) { final int pos = sourceCharacters.indexOf(sourceString[i]); result[i] = pos!=-1 ? targetCharactersArray[pos] : sourceString[i]; } // result String resultString = new String(result); Any ideas? Btw, the UTF-8 characters are causing the trouble, with US_ASCII it works fine.

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  • Is there a limit for the number of files in a directory on an SD card?

    - by jamesh
    I have a project written for Android devices. It generates a large number of files, each day. These are all text files and images. The app uses a database to reference these files. The app is supposed to clear up these files after a little use (perhaps after a few days), but this process may or may not be working. This is not the subject of this question. Due to a historic accident, the organization of the files are somewhat naive: everything is in the same directory; a .hidden directory which contains a zero byte .nomedia file to prevent the MediaScanner indexing it. Today, I am seeing an error reported: java.io.IOException: Cannot create: /sdcard/.hidden/file-4200.html at java.io.File.createNewFile(File.java:1263) Regarding the sdcard, I see it has plenty of storage left, but counting $ cd /Volumes/NO_NAME/.hidden $ ls | wc -w 9058 Deleting a number of files seems to have allowed the file creation for today to proceed. Regrettably, I did not try touching a new file to try and reproduce the error on a commandline; I also deleted several hundred files rather than a handful. However, my question is: are there hard limits on filesize or number of files in a directory? am I even on the right track here? Nota Bene: The SD card is as-is - i.e. I haven't formatted it, so I would guess it would be a FAT-* format. The FAT-32 format has hard limits of filesize of 2GB (well above the filesizes I am dealing with) and a limit of number of files in the root directory. I am definitely not writing files in the root directory.

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  • SQLce DAL Linq to Sql or EntityFramework

    - by bretddog
    Hi, I'm learning databases, using SqlCe, and need business object to database mapping. Currently I try to decide if to use Linq to Sql, or EntityFramework. (I understand a bit L2S, but haven't familiarized with EF yet) The program will only be debeloped and used by myself, so I have good control of the priorities: I don't need to consider potential change of database type or data storage type, as I'm quite certain SQLce will stay sufficient. I DO expect continued development and changes to the data scheme while the program is in active use; change business object properties (Hence database columns), and possibly overall table scheme. So old data must be transported to new scheme. I also want to keep a decent degree of layer separation DAL/BLL, although this may not be necessary, it is good for me to learn these principles. My question is: With these priorities, would I have any benefit by choosing either Linq2Sql vs. EntityFramwork? (and please explain why) Btw, the project involves very simple table scheme with only 4-5 tables and very simple relations. Thanks!

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  • EC2 persistence of machine

    - by Seagull
    I want to 'persist' my Amazon EC2 images. My scenario: I have a range of Windows and Linux machines Some machines are EBS backed, whereas others are S3 backed. I need to be able to persist a machine (put it to sleep), preferably keeping all settings active I had them when the machine was running. I need to be able to quickly wake up a machine from sleep [Ideally with an SLA of less than 2 min to turn-on, if such an SLA is available with Amazon]. Here's the stuff that confuses me: AWS allows me to put EBS backed machines to sleep, but not S3 backed. I believe I can put S3 machines into some sort of persistence mode. But this involves shutting down the machine, writing it to S3 storage and then recovering from there (not a real sleep mode, but at least I don't continue to get billed for CPU). S3 backing seems to take a long time to either writing a machine to disk, or to recover (turn on a machine). I can't tell immediately which machines are EBS backed and which are S3 backed? It seems like I can instantiate either type, but it's not immediately clear how Amazon decided whether a given machine should be EBS or S3 backed. Advice?

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  • handling large arrays with array_diff

    - by bigmac
    I have been trying to compare two arrays. Using array_intersect presents no problems. When using array_diff and arrays with ~5,000 values, it works. When I get to ~10,000 values, the script dies when I get to array_diff. Turning on error_reporting did not produce anything. I tried creating my own array_diff function: function manual_array_diff($arraya, $arrayb) { foreach ($arraya as $keya => $valuea) { if (in_array($valuea, $arrayb)) { unset($arraya[$keya]); } } return $arraya; } source: http://stackoverflow.com/questions/2479963/how-does-array-diff-work I would expect it to be less efficient that than the official array_diff, but it can handle arrays of ~10,000. Unfortunately, both array_diffs fail when I get to ~15,000. I tried the same code on a different machine and it runs fine, so it's not an issue with the code or PHP. There must be some limit set somewhere on that particular server. Any idea how I can get around that limit or alter it or just find out what it is?

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  • Binary Search Tree for specific intent

    - by Luís Guilherme
    We all know there are plenty of self-balancing binary search trees (BST), being the most famous the Red-Black and the AVL. It might be useful to take a look at AA-trees and scapegoat trees too. I want to do deletions insertions and searches, like any other BST. However, it will be common to delete all values in a given range, or deleting whole subtrees. So: I want to insert, search, remove values in O(log n) (balanced tree). I would like to delete a subtree, keeping the whole tree balanced, in O(log n) (worst-case or amortized) It might be useful to delete several values in a row, before balancing the tree I will most often insert 2 values at once, however this is not a rule (just a tip in case there is a tree data structure that takes this into account) Is there a variant of AVL or RB that helps me on this? Scapegoat-trees look more like this, but would also need some changes, anyone who has got experience on them can share some thougts? More precisely, which balancing procedure and/or removal procedure would help me keep this actions time-efficient?

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  • Django Querysets -- need a less expensive way to do this..

    - by rh0dium
    Hi all, I have a problem with some code and I believe it is because of the expense of the queryset. I am looking for a much less expensive (in terms of time) way to to this.. log.info("Getting Users") employees = Employee.objects.filter(is_active = True) log.info("Have Users") if opt.supervisor: if opt.hierarchical: people = getSubs(employees, " ".join(args)) else: people = employees.filter(supervisor__name__icontains = " ".join(args)) else: log.info("Filtering Users") people = employees.filter(name__icontains = " ".join(args)) | \ employees.filter(unix_accounts__username__icontains = " ".join(args)) log.info("Filtered Users") log.info("Processing data") np = [] for person in people: unix, p4, bugz = "No", "No", "No" if len(person.unix_accounts.all()): unix = "Yes" if len(person.perforce_accounts.all()): p4 = "Yes" if len(person.bugzilla_accounts.all()): bugz = "Yes" if person.cell_phone != "": exphone = fixphone(person.cell_phone) elif person.other_phone != "": exphone = fixphone(person.other_phone) else: exphone = "" np.append({ 'name':person.name, 'office_phone': fixphone(person.office_phone), 'position': person.position, 'location': person.location.description, 'email': person.email, 'functional_area': person.functional_area.name, 'department': person.department.name, 'supervisor': person.supervisor.name, 'unix': unix, 'perforce': p4, 'bugzilla':bugz, 'cell_phone': fixphone(exphone), 'fax': fixphone(person.fax), 'last_update': person.last_update.ctime() }) log.info("Have data") Now this results in a log which looks like this.. 19:00:55 INFO phone phone Getting Users 19:00:57 INFO phone phone Have Users 19:00:57 INFO phone phone Processing data 19:01:30 INFO phone phone Have data As you can see it's taking over 30 seconds to simply iterate over the data. That is way too expensive. Can someone clue me into a more efficient way to do this. I thought that if I did the first filter that would make things easier but seems to have no effect. I'm at a loss on this one. Thanks To be clear this is about 1500 employees -- Not too many!!

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  • MySql: Query multiple identical dynamic tables.

    - by JYelton
    I have a database with 500+ tables, each with identical structure, that contain historical data from sensors. I am trying to come up with a query that will locate, for example, all instances where sensor n exceeds x. The problem is that the tables are dynamic, the query must be able to dynamically obtain the list of tables. I can query information_schema.tables to get a list of the tables, like so: SELECT table_name FROM information_schema.tables WHERE table_schema = 'database_name'; I can use this to create a loop in the program and then query the database repeatedly, however it seems like there should be a way to have MySql do the multiple table search. I have not been able to make a stored procedure that works, but the examples I can find are generally for searching for a string in any column. I want to specifically find data in a specific column that exists in all tables. I admit I do not understand how to properly use stored procedures nor if they are the appropriate solution to this problem. An example query inside the loop would be: SELECT device_name, sensor_value FROM device_table WHERE sensor_value > 10; Trying the following does not work: SELECT device_name, sensor_value FROM ( SELECT table_name FROM information_schema.tables WHERE table_schema = 'database_name' ) WHERE sensor_value > 10; It results in an error: "Every derived table must have its own alias." The goal is to have a list of all devices that have had a given sensor value occur anywhere in their log (table). Ultimately, should I just loop in my program once I've obtained a list of tables, or is there a query structure that would be more efficient?

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  • Sparse (Pseudo) Infinite Grid Data Structure for Web Game

    - by Ming
    I'm considering trying to make a game that takes place on an essentially infinite grid. The grid is very sparse. Certain small regions of relatively high density. Relatively few isolated nonempty cells. The amount of the grid in use is too large to implement naively but probably smallish by "big data" standards (I'm not trying to map the Internet or anything like that) This needs to be easy to persist. Here are the operations I may want to perform (reasonably efficiently) on this grid: Ask for some small rectangular region of cells and all their contents (a player's current neighborhood) Set individual cells or blit small regions (the player is making a move) Ask for the rough shape or outline/silhouette of some larger rectangular regions (a world map or region preview) Find some regions with approximately a given density (player spawning location) Approximate shortest path through gaps of at most some small constant empty spaces per hop (it's OK to be a bad approximation often, but not OK to keep heading the wrong direction searching) Approximate convex hull for a region Here's the catch: I want to do this in a web app. That is, I would prefer to use existing data storage (perhaps in the form of a relational database) and relatively little external dependency (preferably avoiding the need for a persistent process). Guys, what advice can you give me on actually implementing this? How would you do this if the web-app restrictions weren't in place? How would you modify that if they were? Thanks a lot, everyone!

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  • Trouble with custom WPF Panel-derived class

    - by chaiguy
    I'm trying to write a custom Panel class for WPF, by overriding MeasureOverride and ArrangeOverride but, while it's mostly working I'm experiencing one strange problem I can't explain. In particular, after I call Arrange on my child items in ArrangeOverride after figuring out what their sizes should be, they aren't sizing to the size I give to them, and appear to be sizing to the size passed to their Measure method inside MeasureOverride. Am I missing something in how this system is supposed to work? My understanding is that calling Measure simply causes the child to evaluate its DesiredSize based on the supplied availableSize, and shouldn't affect its actual final size. Here is my full code (the Panel, btw, is intended to arrange children in the most space-efficient manner, giving less space to rows that don't need it and splitting remaining space up evenly among the rest--it currently only supports vertical orientation but I plan on adding horizontal once I get it working properly): protected override Size MeasureOverride( Size availableSize ) { foreach ( UIElement child in Children ) child.Measure( availableSize ); return availableSize; } protected override System.Windows.Size ArrangeOverride( System.Windows.Size finalSize ) { double extraSpace = 0.0; var sortedChildren = Children.Cast<UIElement>().OrderBy<UIElement, double>( new Func<UIElement, double>( delegate( UIElement child ) { return child.DesiredSize.Height; } ) ); double remainingSpace = finalSize.Height; double normalSpace = 0.0; int remainingChildren = Children.Count; foreach ( UIElement child in sortedChildren ) { normalSpace = remainingSpace / remainingChildren; if ( child.DesiredSize.Height < normalSpace ) // if == there would be no point continuing as there would be no remaining space remainingSpace -= child.DesiredSize.Height; else { remainingSpace = 0; break; } remainingChildren--; } extraSpace = remainingSpace / Children.Count; double offset = 0.0; foreach ( UIElement child in Children ) { //child.Measure( new Size( finalSize.Width, normalSpace ) ); double value = Math.Min( child.DesiredSize.Height, normalSpace ) + extraSpace; child.Arrange( new Rect( 0, offset, finalSize.Width, value ) ); offset += value; } return finalSize; }

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  • Create a new delegate class for each asynchronous image download?

    - by Charles S.
    First, I'm using an NSURLConnection to download JSON data from twitter. Then, I'm using a second NSURLConnection to download corresponding user avatar images (the urls to the images are parsed from the first data download). For the first data connection, I have my TwitterViewController set as the NSURLConnection delegate. I've created a separate class (ImageDownloadDelegate) to function as the delegate for a second NSURLConnection that handles the images. After the tweets are finished downloading, I'm using this code to get the avatars: for(int j=0; j<[self.tweets count]; j++){ ImageDownloadDelegate *imgDelegate = [[ImageDownloadDelegate alloc] init]; Tweet *myTweet = [self.tweets objectAtIndex:j]; imgDelegate.tweet = myTweet; imgDelegate.table = timeline; NSURLRequest* request = [NSURLRequest requestWithURL:[NSURL URLWithString:myTweet.imageURL] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60]; imgConnection = [[NSURLConnection alloc] initWithRequest:request delegate:imgDelegate]; [imgDelegate release]; } So basically a new instance of the delegate class is created for each image that needs to be downloaded. Is this the best way to go about this? But then there's no way to figure out which image is associate with which tweet, correct? The algorithm works fine... I'm just wondering if I'm going about it the most efficient way.

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  • Partially constructed object / Multi threading

    - by reto
    Heya! I'm using joda due to it's good reputation regarding multi threading. It goes great distances to make multi threaded date handling efficient, for example by making all Date/Time/DateTime objects immutable. But here's a situation where I'm not sure if Joda is really doing the right thing. It probably is correct, but I'd be very interested to see the explanation for it. When a toString() of a DateTime is being called Joda does the following: /* org.joda.time.base.AbstractInstant */ public String toString() { return ISODateTimeFormat.dateTime().print(this); } All formatters are thread safe, as they are as well ready-only. But what's about the formatter-factory: private static DateTimeFormatter dt; /* org.joda.time.format.ISODateTimeFormat */ public static DateTimeFormatter dateTime() { if (dt == null) { dt = new DateTimeFormatterBuilder() .append(date()) .append(tTime()) .toFormatter(); } return dt; } This is a common pattern in single threaded applications. I see the following dangers: Race condition during null check -- worst case: two objects get created. No Problem, as this is solely a helper object (unlike a normal singleton pattern situation), one gets saved in dt, the other is lost and will be garbage collected sooner or later. the static variable might point to a partially constructed object before the objec has been finished initialization (before calling me crazy, read about a similar situation in this Wikipedia article. So how does Joda ensure that not partially created formatter gets published in this static variable? Thanks for your explanations! Reto

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  • Sorting by custom field and fetching whole tree from DB

    - by Niaxon
    Hello everyone, I am trying to do file browser in a tree form and have a problem to sort it somehow. I use PHP and MySQL for that. I've created mixed (nested set + adjacency) table 'element' with the following fields: element_id, left_key, right_key, level, parent_id, element_name, element_type (enum: 'folder','file'), element_size. Let's not discuss right now that it is better to move information about element (name, type, size) into other table. Function to scan specified directory and fill table work correctly. Noteworthy, i am adding elements to tree in specific order: folders first and then files. After that i can easily fetch and display whole table on the page using simple query: SELECT * FROM element WHERE 1=1 ORDER BY left_key With the result of that query and another function i can generate correct html code (<ul><li>... and so on). to display tree. Now back to the question (finally, huh?). I am struggling to add sorting functionality. For example i want to order my result by size. Here i need to keep in my mind whole hierarchy of tree and rule: folders first, files later. I believe i can do that by generating in PHP recursive query: SELECT * FROM element WHERE parent_id = {$parentId} ORDER BY element_type (so folders would be first), size (or name for example) asc/desc After that for each result which has type = 'folder' i will send another query to get it's content. Also it's possible to fetch whole tree by left_key and after that sort it in PHP as array but i guess that would be worse :) I wonder if there is better and more efficient way to do such a thing?

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  • Prototypal inheritance should save memory, right?

    - by Techpriester
    Hi Folks, I've been wondering: Using prototypes in JavaScript should be more memory efficient than attaching every member of an object directly to it for the following reasons: The prototype is just one single object. The instances hold only references to their prototype. Versus: Every instance holds a copy of all the members and methods that are defined by the constructor. I started a little experiment with this: var TestObjectFat = function() { this.number = 42; this.text = randomString(1000); } var TestObjectThin = function() { this.number = 42; } TestObjectThin.prototype.text = randomString(1000); randomString(x) just produces a, well, random String of length x. I then instantiated the objects in large quantities like this: var arr = new Array(); for (var i = 0; i < 1000; i++) { arr.push(new TestObjectFat()); // or new TestObjectThin() } ... and checked the memory usage of the browser process (Google Chrome). I know, that's not very exact... However, in both cases the memory usage went up significantly as expected (about 30MB for TestObjectFat), but the prototype variant used not much less memory (about 26MB for TestObjectThin). I also checked: The TestObjectThin instances contain the same string in their "text" property, so they are really using the property of the prototype. Now, I'm not so sure what to think about this. The prototyping doesn't seem to be the big memory saver at all. I know that prototyping is a great idea for many other reasons, but I'm specifically concerned with memory usage here. Any explanations why the prototype variant uses almost the same amount of memory? Am I missing something?

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  • Return unordered list from hierarchical sql data

    - by Milan
    I have table with pageId, parentPageId, title columns. Is there a way to return unordered nested list using asp.net, cte, stored procedure, UDF... anything? Table looks like this: PageID ParentId Title 1 null Home 2 null Products 3 null Services 4 2 Category 1 5 2 Category 2 6 5 Subcategory 1 7 5 SubCategory 2 8 6 Third Level Category 1 ... Result should look like this: Home Products Category 1 SubCategory 1 Third Level Category 1 SubCategory 2 Category 2 Services Ideally, list should contain <a> tags as well, but I hope I can add it myself if I find a way to create <ul> list. EDIT 1: I thought that already there is a solution for this, but it seems that there isn't. I wanted to keep it simple as possible and to escape using ASP.NET menu at any cost, because it uses tables by default. Then I have to use CSS Adapters etc. Even if I decide to go down the "ASP.NET menu" route I was able to find only this approach: http://aspalliance.com/822 which uses DataAdapter and DataSet :( Any more modern or efficient way?

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