MSDN on throwing exceptions. By catching a more general exception, you hide programming errors inside the try-block. For example, a NullReferenceException would be swallowed, and make it a lot harder to notice. Additionally, any recovery code you have in the catch-block might not work as intended for other than the specific exception it was written for. A good article on handling exceptions. However, if you pass a CancellationToken into an async function and it uses CancellationToken.

Without looking inside, it's impossible to know which exception the async function might throw. If you need the TaskCanceledException, for example to access its Task property, you can catch that as well before catching the OperationCanceledException.

Or you can try to cast the caught OperationCanceledException into it. Generally, When you make an error, you want to be notified about it as loud and clear as possible. The default behavior for Visual Studio is to only break debugger on uncaught exceptions.

Now, if you have some generic catches in place to swallow exceptions, for example from some of your secondary components, such as analytics, you'd miss the unwanted behavior. On Visual Studio go to: On Visual Studio and go to: If you are using any synchronous APIs that throw exceptions even in expected cases, you might have to leave those unchecked. Sometimes you want to catch an exception and rethrow it as is or with additional information.

For example:. Some APIs like to throw exceptions even on expected cases. Check, for example, the next practice for explanation on why this is not necessarily the best kind of behavior. One good example of such API is Windows. HttpClient, which throws Exceptions on network errors. A network error is hardly an unexpected event. Fortunately, there's a way to utilize Task on asynchronous methods to avoid getting the exception thrown into your code while still handling it.

For example, here we convert all network errors to HttpStatusCode. RequestTimeout without letting an exception to be thrown:. On Windows 8 you can merge this registry entry to enable storing dumps into C: On Window 8, you can also generate dumps manually by right clicking your app in the Task Manager and choosing "create dump file". Dumps can be analyzed for example using Visual Studio or WinDbg. Notice that there are two of them now: HttpClient and Windows. The latter was added to Windows 8. More importantly System. Http might be made unavailable for Windows Store Apps in the future.

Additionally, the Windows. One useful thing to know about the Windows. You can get the actual reason with Windows. When ever you are serializing values that can be represented differently in different cultures, make sure that you serialize and deserialize them with the same culture. If you don't define the culture explicitly, the APIs normally use the culture of the current thread, which is often set by a setting in the operating system. InvariantCulture is an IFormatProvider that exists exactly for the purpose of hardocoding the culture for serializations. For example, serialization of DateTime, double, float, and decimal depend on culture.

If you serialize these values using the OS provided culture, and the culture has changed when you deserialize, you are likely to run into runtime exceptions. MSDN , Channel9. Windows 10 store limits the visibility of apps based on the store description languages and the selected language of the device. For example, if your app only has a store description in Finnish, it won't show up on devices that have their primary language set to English or Swedish - A very common case in Finland.

Exempt to this rule seems to be en-US, which seems to act as a 'locale for everybody'. If your app also has an en-US store description, it is apparently visible for all users. There are different timers for different purposes. Additionally there are Observable. Timer , Task. Delay , and last and least Thread.

Lazy loading is a concept of deferring loading of an object until the object is actually needed. It doesn't necessary mean creation of a new instance of an object, but often involves a heavy operation that returns an object.

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Lazy can save memory and unnecessary processing in cases where running a heavy operation or creation of a heavy object is only needed in optional or late execution paths. C 6 allows for a very concise and low overhead lazy properties for the simplest cases. Note that this approach isn't thread safe and doesn't consider null to be a legitimate 'loaded' value, but should work just fine for constrained cases. Notice that if HeavyOperation returns null, it will be called again on the next time Heavy is accessed.

There are at least three other ways to implement lazy loading in.

Lazy, LazyInitializer, and ThreadLocal. All of these are explained at MSDN , but to summarize:. It will automatically return empty IEnumerable if no "yield return" is called. This will avoid null reference exceptions when you're expecting to get an IEnumerable.

c# - Scheduling a timed background task in windows store app - Stack Overflow

The yield approach also only runs as far as is required by the possible iterator. For example, the following only creates one Galaxy instance, avoiding unnecessary processing. Probably the 1 thing to know about LINQ is that it creates a query that is executed whenever its items are accessed. Sometimes this is what you actually want. However, often you just want to run the query once but access the resulting items multiple times. To avoid unnecessary re-evaluation and bugs resulting from the query result changing, use ToArray, ToList, etc.

ItemsStackPanel was added into Windows 8. If item grouping is used, VirtualizingStackPanel realizes the whole group of items even if only the first one was required. ItemsStackPanel handles items virtualization correctly also when groups are used and will therefore offer better performance. MSDN Blog. There are two main ways to 'package' a piece of UI into a reusable component. Essentially both of them are partial definitions of the same class.

Additionally, UserControls are loaded even if they are created with Collapsed Visibility, while Templated Controls are only be loaded when their Visibility is set to Visible. These details can have significant effect on performance, especially if the controls are used in list items. Templated controls also offer better reusability with re-templating and styling. This will add a new class that inherits from Control and sets the DefaultStyleKey in it's constructor, as well as adds an empty default style for the control into Generic. Templated controls and user controls have also been discussed in this issue.

Dependent animations are animations that depend on the UI thread, the major drawback is performance. Independent animations are animations that can be run independent of the UI thread and therefore don't burden it and remain smooth even if the UI thread is blocked. For implementing animations you should use Storyboards. According to MSDN , all of the following types of animations are guaranteed to be independent:. Additionally you should use animations from the Windows. Animation namespace when possible. The animations have "Theme" in their class name, and are described in Quickstart: Animating your UI using library animations.

Parse yourXamlString directly in C. However, if your XAML references for example a control in another class library, the user of your library has to add a reference to that library as well. First add for example a Resources. You can then load the ResourceDictionary by creating a new ResourceDictionary instance and setting it's source as follows:. Now you can also merge the ResourceDictionary to the app's App.

Then the named resources can be accessed via Application. Resources and be overridden in the App. If you aren't already using a library that offers you an easy way to bind into your reactive code from XAML, here's one that offers ReactiveProperty, ReactiveCommand and some other useful classes. Code is often split into small methods for reusability.

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However, there are reasons to split your methods even if you don't plan to reuse them. Method name documents the intent of the code it encloses. This gives you more informative callstack view while debugging and better stacktraces from your exceptions. The stacktraces part applies especially to release builds, where source code line information is lost. Exceptions from synchronous methods propagate up the call stack regardless if you use the possible return value or not.

Awaitable methods work a bit differently. When an unhandled exception is thrown within an awaitable method, the exception is wrapped into the task object returned by the method. When you access the Result or await the method within a try block, you can catch the unhandled exceptions from the awaitable method normally. Additionally, you can observe the exception by accessing the task's Exception property. I have a list of of StringsDouble called Messages. The code for the class is below: How can i accomplish this?

I believe i need to use a background task, but how can i schedule it to run every 5 minutes? You can use DispatcherTimer on UI thread: FromMinutes 5 ; timer. Start ; or ThreadPoolTimer on a background thread: FromMinutes 5 ;. There is no way to run your backgroundtask every 5 minutes. Change the Name of the label to textLabel , change the Text property to "Demo" or any other text used like to display, modify the label's Font property so it displays a larger font, and change the ForeColor to something other than black so the text is visible on the black background.

An example of my form is displayed below. The size of the form is not important since we will be resizing it programmatically later. Now press F7 to view the code behind the form.

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Add the following constructor which sets the form's Bounds: When the form loads, we want to hide the cursor and raise the form in front of all other visible windows. To do this, we will first add a Load event handler to the form. An event handler is a function which executes in response to a particular event. To add an event handler, first view the form in Design mode click the tab labeled ScreenSaverForm. Choose the ScreenSaverForm from the drop-down list in the Properties window and click on the lightning bolt which lists all the form's events.

Below is a picture of my Properties window. Scroll down to the Load event and double-click on the word "Load". This will create a Load event handler for you and move you back to viewing the form's code. Type the two lines of code inside this function: Do not run your application just yet!

How to add a BackgroundTask

If you do, you cannot terminate the screen saver unless you use the Task Manager. That's because we only made the form visible in Program. We need to first add some logic that will terminate the app when a key is pressed or when the mouse is clicked or moved. Do this in the same way you added the Load event handler by scrolling through the ScreenSaverForm 's list of events in the Properties window and double-clicking on each event. After the event handlers have been setup, then type in the code below. If you merely copy and paste all the code below into your program without setting up the event handlers properly, the event handlers will not be called!

Visual Studio has to write special code to attach these event handlers to the form. If you are really curious what this code looks like, take a look at the code in the ScreenSaverForm. Don't change the contents of this file unless you really know what you are doing since this file is auto-generated by Visual Studio. Abs mouseLocation. You can play with smaller or larger values than 5 if you'd like.

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If you now run your application Ctrl-F5 , you'll see that it does nothing That's because we are not sending it any command line arguments, and we have not yet implemented the configuration part of the screen saver. Save the project and press Ctrl-F5. The entire screen should turn black, and the text should display at a fixed location. Pressing the mouse or moving it or pressing the keyboard will kill the application. You can change the to smaller or larger numbers to speed up or slow down the rate at which the text is re-positioned on the screen.

Next Math. Max 1, Bounds. Width - textLabel. Width ; textLabel. Height - textLabel. Run the program again, and this time the text will move to different locations every 3 seconds. Press or move the mouse to terminate the application. The screenshot below shows the screen saver running in preview mode on my Windows 7 computer:.

If you'd prefer not to implement a preview mode, you don't have to. We will implement a preview mode for our program because all it entails is using some Windows API functions and changing the font size of our text label. In Program. Show "Sorry, but the expected window handle was not provided. Parse secondArgument ; Application. Otherwise the application is started using a special constructor for the ScreenSaverForm which we'll need to write next. Go back to ScreenSaverForm.