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  • Parameter passed by const reference returned by const reference.

    - by Alien01
    Hello, I was reading C++ Faq Second Edition , faq number 32.08 . FAQ says that parameter passed by const reference and returned by const reference can cause dangling reference. But it is ok if parameter is passed by reference and returned by reference. I got it that it is unsafe in case of const reference but how is it safe in case when parameter is non const reference. Last line of FAQ says "Note that if a function accepts a parameter by non-const reference (for example, f(string& s)), returning a copy of this reference parameter is safe because a temporary cannot be passed by non-const reference." Need some insight on this!!

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  • What question(s) does an object's behavior answer?

    - by Corwin
    Reading a book I have found the following statement: (Object) Behaviors answer either of two questions: What does this object do (for me)? or What can I do to this object? In the case of an orange, it doesn’t do a whole lot, but we can do things to it. One behavior is that it can be eaten. In my understanding of object behaviour the statement above is correct regarding the first question and is incorrect in case of the second. However, I often see classes with methods like Orange::eat(), and this makes me uncertain about my design skills. So I would like to ask is it a design mistake to give oranges a behaviour eat? (oranges and eat are used just for example)

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  • How to bind value to its parent element value?

    - by KentZhou
    Silverlight provides element to element binding. How to apply it this is case: I have a xaml as below: <TextBlock Text="{Binding ABC}" > <ToolTipService.ToolTip> <local:MyControl Title="{Binding ...}" /> </ToolTipService.ToolTip> </TextBlock> I want to bind MyControl Title to the same data as its parent Textblock Text, but I don't want set x:Name for its parent Textblock. I know there is one solution to bind Title to same data source: <local:MyControl Title="{Binding ABC}" /> This may cause two times to call "{Binding ABC}", with my case, there ValurConverter for this binding. I don't want to use this way.

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  • Error handling and polymorphism

    - by Neeraj
    I have an application with some bunch of code like this: errCode = callMainSystem(); switch (errCode){ case FailErr: error("Err corresponding to val1\n"); case IgnoreErr: error("Err corresponding to val2\n"); ... ... default: error("Unknown error\n"); } The values are enum constants. Will it make some sense to have something like: // Error* callMainSystem() ... Some code return FaileErr(); // or some other error // handling code Error* err = callMainSystem(); err->toString(); The Error class may be made singleton as it only has to print error messages. What are the pros and cons of above methods,size is an important criteria as the application needs to be supported on embedded devices as well. P.S: I don't want to use exception handling because of portability issues and associated overheads.

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  • Dynamically Creating Flex Components In ActionScript

    - by Joshua
    Isn't there some way to re-write the following code, such that I don't need a gigantic switch statement with every conceivable type? Also, if I can replace the switch statement with some way to dynamically create new controls, then I can make the code smaller, more direct, and don't have to anticipate the possibility of custom control types. Before: <?xml version="1.0" encoding="utf-8"?> <mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml" layout="vertical"> <mx:Script> <![CDATA[ import mx.containers.HBox; import mx.controls.Button; import mx.controls.Label; public function CreateControl(event:Event):void { var Type:String=Edit.text; var NewControl:Object; switch (Type) { case 'mx.controls::Label':NewControl=new Label();break; case 'mx.controls::Button':NewControl=new Button();break; case 'mx.containers::HBox':NewControl=new HBox();break; ... every other type, including unforeseeable custom types } this.addChild(NewControl as DisplayObject); } ]]> </mx:Script> <mx:Label text="Control Type"/> <mx:TextInput id="Edit"/> <mx:Button label="Create" click="CreateControl(event);"/> </mx:WindowedApplication> AFTER: <?xml version="1.0" encoding="utf-8"?> <mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml" layout="vertical"> <mx:Script> <![CDATA[ import mx.containers.HBox; import mx.controls.Button; import mx.controls.Label; public function CreateControl(event:Event):void { var Type:String=Edit.text; var NewControl:Object= *???*(Type); this.addChild(NewControl as DisplayObject); } ]]> </mx:Script> <mx:Label text="Control Type"/> <mx:TextInput id="Edit"/> <mx:Button label="Create" click="CreateControl(event);"/> </mx:WindowedApplication>

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  • Recommendations with hierarchical data on non-relational databases?

    - by Luki
    I'm developing an web application that uses a non-relational database as a backend (django-nonrel + AppEngine). I need to store some hierarchical data (projects/subproject_1/subproject_N/tasks), and I'm wondering which pattern should I use. For now I thought of: Adjacency List (store the item's parent id) Nested sets (store left and right values for the item) In my case, the depth of nesting for a normal user will not exceed 4-5 levels. Also, on the UI, I would like to have a pagination for the items on the first level, to avoid to load too many items at the first page load. From what I understand so far, nested sets are great when the hierarchy is used more for displaying. Adjacency lists are great when editing on the tree is done often. In my case I guess I need the displaying more than the editing (when using nested sets, even if the display would work great, the above pagination could complicate things on editing). Do you have any thoughts and advice, based on your experience with the non-relational databases?

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  • Eager loading in EF1.0

    - by Dave Swersky
    I have a many-to-many relationship: Application - Applications_Servers - Server This is set up in my Entity Data Model and all is well. My problem is that I'd like to eager-load the whole graph of Applications so that I have an IEnumerable<Applications>, each Application member populated with the Servers collection associated by the many-to-many relationship. Normally this wouldn't be a problem, but according to my research there must be a navigation property between Application and Server. This is not the case for me because my Applications_Servers join table has more in it than just the two keys. Therefore, there is no navigation property directly between Application and Server, and this doesn't work: var apps = (from a in context.Application.Include("Server") select a).ToList(); I get an error saying there is no navigation property on Application called "Server", and that's correct, there is none. How do I write the query to eager-load my Applications with their Servers in this case?

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  • Errors in Layout Cant figure it out!!

    - by Wahid
    Please Help. I'm trying to create a menu that pops up if an android user clicks "menu" on his phone. and i want on the screen a button so when the user clicks it a sound starts playing for a second or two. && this error keeps popping up in my java class in the part where it says " public boolean onCreateTutorial(Menu menu) {" heres my code. package com.Tutorial; import com.Tutorial.R; import android.app.Activity; import android.os.Bundle; import android.view.Menu; import android.view.MenuInflater; import android.view.MenuItem; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.Toast; public class Tutorial extends Activity { private SoundManager mSoundManager; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mSoundManager = new SoundManager(); mSoundManager.initSounds(getBaseContext()); mSoundManager.addSound(1, R.raw.sound); Button SoundButton = (Button)findViewById(R.id.Button); SoundButton.setOnClickListener(new OnClickListener() { public void onClick(View v) { mSoundManager.playSound(1); @Override public boolean onCreateTutorial(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.menu, menu); return true; } } @Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case R.id.icon: Toast.makeText(this, "Rate this app on Android Market!", Toast.LENGTH_LONG).show(); break; case R.id.text: Toast.makeText(this, "Name: Wahid", Toast.LENGTH_LONG).show(); break; case R.id.icontext: Toast.makeText(this, "MeSoundFx Pro on the Android Market! (Coming Soon)", Toast.LENGTH_LONG).show(); break; } return true; } }); } }

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  • Dynamic Dispatch without Virtual Functions

    - by Kristopher Johnson
    I've got some legacy code that, instead of virtual functions, uses a kind field to do dynamic dispatch. It looks something like this: // Base struct shared by all subtypes // Plain-old data; can't use virtual functions struct POD { int kind; int GetFoo(); int GetBar(); int GetBaz(); int GetXyzzy(); }; enum Kind { Kind_Derived1, Kind_Derived2, Kind_Derived3 }; struct Derived1: POD { Derived1(): kind(Kind_Derived1) {} int GetFoo(); int GetBar(); int GetBaz(); int GetXyzzy(); // plus other type-specific data and function members }; struct Derived2: POD { Derived2(): kind(Kind_Derived2) {} int GetFoo(); int GetBar(); int GetBaz(); int GetXyzzy(); // plus other type-specific data and function members }; struct Derived3: POD { Derived3(): kind(Kind_Derived3) {} int GetFoo(); int GetBar(); int GetBaz(); int GetXyzzy(); // plus other type-specific data and function members }; and then the POD class's function members are implemented like this: int POD::GetFoo() { // Call kind-specific function switch (kind) { case Kind_Derived1: { Derived1 *pDerived1 = static_cast<Derived1*>(this); return pDerived1->GetFoo(); } case Kind_Derived2: { Derived2 *pDerived2 = static_cast<Derived2*>(this); return pDerived2->GetFoo(); } case Kind_Derived3: { Derived3 *pDerived3 = static_cast<Derived3*>(this); return pDerived3->GetFoo(); } default: throw UnknownKindException(kind, "GetFoo"); } } POD::GetBar(), POD::GetBaz(), POD::GetXyzzy(), and other members are implemented similarly. This example is simplified. The actual code has about a dozen different subtypes of POD, and a couple dozen methods. New subtypes of POD and new methods are added pretty frequently, and so every time we do that, we have to update all these switch statements. The typical way to handle this would be to declare the function members virtual in the POD class, but we can't do that because the objects reside in shared memory. There is a lot of code that depends on these structs being plain-old-data, so even if I could figure out some way to have virtual functions in shared-memory objects, I wouldn't want to do that. So, I'm looking for suggestions as to the best way to clean this up so that all the knowledge of how to call the subtype methods is centralized in one place, rather than scattered among a couple dozen switch statements in a couple dozen functions. What occurs to me is that I can create some sort of adapter class that wraps a POD and uses templates to minimize the redundancy. But before I start down that path, I'd like to know how others have dealt with this.

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  • Java 7 API design best practice - return Array or return Collection

    - by Shengjie
    I know this question has be asked before generic comes out. Array does win out a bit given Array enforces the return type, it's more type-safe. But now, with latest JDK 7, every time when I design this type of APIs: public String[] getElements(String type) vs public List<String> getElements(String type) I am always struggling to think of some good reasons to return A Collection over An Array or another way around. What's the best practice when it comes to the case of choosing String[] or List as the API's return type? Or it's courses for horses. I don't have a special case in my mind, I am more looking for a generic pros/cons comparison.

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  • generating dynamic word documents for mass mailing

    - by bluesystem
    I need to generate a mass mailing based on a word document model with PHP. Given is a database with the adresses and the data that need to be filled in my word model. I want to generate a single word document with the different adresses and field contents from the database. We have a Linux server and the COM object is not avalaible. Is there a ready to use class to do this? Did you had any experiance with PHPWord? What is the best practice in this case? In the ideal case the client should just upload th word master document, with the fields that need to be filled and then fusioned to a multiple pages word document containing the whole mailing.

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  • Approximate photo of a simple drawing using lines

    - by user3704596
    As an input I have a photo of a simple symbol, e.g.: https://www.dropbox.com/s/nrmsvfd0le0bkke/symbol.jpg I would like to detect the straight lines in it, like points of start and ends of the lines. In this case, assuming the top left of the symbol is (0,0), the lines would be defined like this: start end (coordinates of beginning and end of a line) 1. (0,0); (0,10) (vertical line) 2. (0,10); (15, 15) 3. (15,15); (0, 20) 4. (0,20); (0,30) How can I do it (pereferably using OpenCV)? I though about Hough lines, but they seem to be good for perfect thin straight lines, which is not the case in a drawing. I'll probably work on binarized image, too.

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  • Which is the "best" data access framework/approach for C# and .NET?

    - by Frans
    (EDIT: I made it a community wiki as it is more suited to a collaborative format.) There are a plethora of ways to access SQL Server and other databases from .NET. All have their pros and cons and it will never be a simple question of which is "best" - the answer will always be "it depends". However, I am looking for a comparison at a high level of the different approaches and frameworks in the context of different levels of systems. For example, I would imagine that for a quick-and-dirty Web 2.0 application the answer would be very different from an in-house Enterprise-level CRUD application. I am aware that there are numerous questions on Stack Overflow dealing with subsets of this question, but I think it would be useful to try to build a summary comparison. I will endeavour to update the question with corrections and clarifications as we go. So far, this is my understanding at a high level - but I am sure it is wrong... I am primarily focusing on the Microsoft approaches to keep this focused. ADO.NET Entity Framework Database agnostic Good because it allows swapping backends in and out Bad because it can hit performance and database vendors are not too happy about it Seems to be MS's preferred route for the future Complicated to learn (though, see 267357) It is accessed through LINQ to Entities so provides ORM, thus allowing abstraction in your code LINQ to SQL Uncertain future (see Is LINQ to SQL truly dead?) Easy to learn (?) Only works with MS SQL Server See also Pros and cons of LINQ "Standard" ADO.NET No ORM No abstraction so you are back to "roll your own" and play with dynamically generated SQL Direct access, allows potentially better performance This ties in to the age-old debate of whether to focus on objects or relational data, to which the answer of course is "it depends on where the bulk of the work is" and since that is an unanswerable question hopefully we don't have to go in to that too much. IMHO, if your application is primarily manipulating large amounts of data, it does not make sense to abstract it too much into objects in the front-end code, you are better off using stored procedures and dynamic SQL to do as much of the work as possible on the back-end. Whereas, if you primarily have user interaction which causes database interaction at the level of tens or hundreds of rows then ORM makes complete sense. So, I guess my argument for good old-fashioned ADO.NET would be in the case where you manipulate and modify large datasets, in which case you will benefit from the direct access to the backend. Another case, of course, is where you have to access a legacy database that is already guarded by stored procedures. ASP.NET Data Source Controls Are these something altogether different or just a layer over standard ADO.NET? - Would you really use these if you had a DAL or if you implemented LINQ or Entities? NHibernate Seems to be a very powerful and powerful ORM? Open source Some other relevant links; NHibernate or LINQ to SQL Entity Framework vs LINQ to SQL

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  • In .net, how do I choose between a Decimal and a Double

    - by Ian Ringrose
    We were discussing this the other day at work and I wish there was a Stackoverflow question I would point people at so here goes.) What is the difference between a Double and a Decimal? When (in what cases) should you always use a Double? When (in what cases) should you always use a Decimal? What’s the diver factors to consider in cases that don’t fall into one of the two camps above? (There a lot of questions that overlap this question, but they tend to be asking what someone should do in a given case, not how to decide in the general case)

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  • Strange WPF Behaviour With WCF Async calls

    - by gvigsgb
    I have a WPF application calling WCF via Async calls. The application has four tabs in which each are loaded from seperate async calls, each tab has a busy indicator. The problem: When running within Visual Studio I can click a refresh button on each tab and each tab's busy indicator starts and the data is retrieved from the WCF service. As each tab's data comes back it is refreshed. When I deploy the application via one click the application's UI hangs after only two tabs start refreshing. So in this case I press refresh on tab one, then on tab two and the application hangs until one of the two tabs data comes back. I thought at first that it was something to do with the WCF service throtteling and that was not the case as both the Visual Studio and the One Click deployments of the application point to the same service. Anyone have any ideas on where to look? I cannot reproduce the hang issue within Visual Studio?

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  • Custom constructors for models in Google App Engine (python)

    - by Nikhil Chelliah
    I'm getting back to programming for Google App Engine and I've found, in old, unused code, instances in which I wrote constructors for models. It seems like a good idea, but there's no mention of it online and I can't test to see if it works. Here's a contrived example, with no error-checking, etc.: class Dog(db.Model): name = db.StringProperty(required=True) breeds = db.StringListProperty() age = db.IntegerProperty(default=0) def __init__(self, name, breed_list, **kwargs): db.Model.__init__(**kwargs) self.name = name self.breeds = breed_list.split() rufus = Dog('Rufus', 'spaniel terrier labrador') rufus.put() The **kwargs are passed on to the Model constructor in case the model is constructed with a specified parent or key_name, or in case other properties (like age) are specified. This constructor differs from the default in that it requires that a name and breed_list be specified (although it can't ensure that they're strings), and it parses breed_list in a way that the default constructor could not. Is this a legitimate form of instantiation, or should I just use functions or static/class methods? And if it works, why aren't custom constructors used more often?

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  • How to interrupt a waiting C++0x thread?

    - by doublep
    I'm considering to use C++0x threads in my application instead of Boost threads. However, I'm not sure how to reimplement what I have with standard C++0x threads since they don't seem to have an interrupt() method. My current setup is: a master thread that manages work; several worker threads that carry out master's commands. Workers call wait() on at least two different condition variables. Master has a "timed out" state: in this case it tells all workers to stop and give whatever result they got by then. With Boost threads master just uses interrupt_all() on a thread group, which causes workers to stop waiting. In case they are not waiting at the moment, master also sets a bool flag which workers check periodically. However, in C++0x std::thread I don't see any replacement for interrupt(). Do I miss something? If not, how can I implement the above scheme so that workers cannot just sleep forever?

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  • What segments does C compiled program use?

    - by b-gen-jack-o-neill
    Hi, I read on OSDev wiki, that protected mode of x86 architecture allow you to create separate segments for code and data, while you cannot write into code section. That Windows (yes, this is the platform) loads new code into code segment, and data are created on data segment. But, if this is the case, how does program know it must switch segments to the data segment? Becouse if I understand it right, all adress instructions point to the segment you run the code from, unless you switch the descriptor. But I also read, that so colled flat memory model allows you to run code and data within one segment. But I read this only in connection to assembler. So, please, what is the case with C compiled code on Windows? Thanks.

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  • Do I have to store a TcpClient even though I only care about its stream?

    - by mafutrct
    A new instance of a TcpClient connects to a remote host. Its NetworkStream is retrieved and stored. Do I have to store the TcpClient itself as well to make sure it is not garbage collected? In case you're going to answer "You have to store it to be able to dispose it": In my specific case, the TcpClient is usually living for a long time (app lifetime), so disposing it is not really a must. However, I agree that, in general, it has to be stored just to be able to call Dispose.

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  • Searching for the right pattern to handle login data

    - by stevebot
    Hi all, I'm working on a controller that handles logins for a Web app. These logins will come from multiple clients but will all contain the same data. However, depending on the client, this data will be interpreted into common entities for our webapp differently. For instance, we have a user code that gets sent in, and in one case we may use the first four digits of the code, and in another case 12 digits of the code to map to a field on a User entity. Instead of handling this all in the controller and having big nasty if blocks of logic, I would like to use a pattern to handle how this information gets ingested into our application. What are your opinions?

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  • Flex Drag & Drop: Detecting when all data has been moved from source to destination

    - by Adam Tuttle
    I have two mx:TileList controls that I'm using to allow editing of objects in batch. The first contains a collection of all available data, and the 2nd contains the current batch. Both are bound to ArrayCollections, and using the native drag-n-drop functionality of the TileList control the data is moved from one ArrayCollection to the other when an object is dragged between them. I need to change the currentState to show & reset the batch manipulation controls when the batch count goes from 0 to n or n to 0 items. Based on the documentation, I would have thought that I should listen to the dragComplete event, but my testing shows that instead of firing after the data has been removed from the source ArrayCollection and added to the destination ArrayCollection, it fires (consistently) between these two actions. Both lists are similar to this: <mx:TileList id="srcList" dragEnabled="true" dropEnabled="true" dragMoveEnabled="true" dataProvider="{images}" dragComplete="handleDragComplete(event)" allowMultipleSelection="true" /> And here's the source of the handleDragComplete function: private function handleDragComplete(e:DragEvent):void{ trace(e.dragInitiator.name + '.dragComplete: batch.length=' + batch.length.toString()); trace(e.dragInitiator.name + '.dragComplete: images.length=' + images.length.toString()); if (batch.length > 0){ currentState = 'show'; }else{ currentState = ''; } } And lastly, here's some example output from running the code. These are all run one after the other. Case 1: The application loads with 10 objects in the first list and the batch is empty. I dragged 1 object from the source list to the batch list. srcList.dragComplete: batch.length=1 srcList.dragComplete: images.length=10 (Expected: 1,9) Clearly, the object has been added to the batch ArrayCollection but not removed from the source. Case 2: Now, I'll drag a 2nd object into the batch. srcList.dragComplete: batch.length=2 srcList.dragComplete: images.length=9 (Expected: 2,8) Firstly, we can see that images.length has changed, showing that the object that I dragged from the source list to the batch list was removed AFTER the dragComplete event fired. The same thing happens this time: The new object is added to the batch ArrayCollection (batch.length=2), the dragComplete event fires (running these traces), and then the object is removed from the source ArrayCollection. Case 3: Now, I'll drag both images from the batch list back to their original location in the source list. batchList.dragComplete: batch.length=2 batchList.dragComplete: images.length=10 (Expected: 0,10) We can see that batch.length hasn't gone down, but the source images array is back at its original length of 10. QUESTION: Am I doing something wrong? Is there another event I could listen for? (Note: I tried both DragExit and DragDrop, just to be sure, and those behave as expected, but are not what I need.) Or is there another way to get the data that I want? Or... have I found a bug in the SDK?

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  • Rails: Ajax-enabled form without a model object

    - by Caffeine Coma
    I'm new to Rails and having a hard time figuring out how to create a form that submits over Ajax without having a corresponding model object. My use case is a simple form that collects an email address and sends it an email; there's nothing to be persisted, so no model. In cases where I do have a model, I've had success with form_for(@model, remote: true). I can't seem to find the right helper for the case where there is no model. I tried form_tag(named_path, remote: true) and that works, but does not use Ajax. Pointers to an example with an example with a proper controller, .html.erb and routes.rb would be really appreciated.

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  • How do I indicate that a class doesn't support certain operators?

    - by romeovs
    I'm writing a class that represents an ordinal scale, but has no logical zero-point (eg time). This scale should permit addition and substraction (operator+, operator+=, ...) but not multiplication. Yet, I always felt it to be a good practice that when one overloads one operator of a certain group (in this case the math operators), one should also overload all the others that belong to that group. In this case that would mean I should need to overload the multiplication and division operators also, because if a user can use A+B he would probable expect to be able the other operators. Is there a method that I can use to throw an error for this at compiler time? The easiest method would be just no to overload the operators operator*, ... yet it would seem appropriate to add a bit more explaination than operator* is not know for class "time". Or is this something that I really should not care about (RTFM user)?

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  • Vibration after regular intervals

    - by umar
    I have a beep system which gives you four beeps. One beep after a second for one second. However If its silent mode i want the vibrator to do the same, vibrate for 1 second 4 times after 1 second. This is the code I am using long[] pattern = new long[2]; pattern[0] = 10; pattern [1] = 30; switch (am.getRingerMode()) { case AudioManager.RINGER_MODE_VIBRATE: vibe.vibrate(pattern, 0); break; case AudioManager.RINGER_MODE_NORMAL: soundsOn(mp); break; Kindly how can i do what i want to do Best Regards

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