| title | ms.date | ms.topic | dev_langs | helpviewer_keywords | ms.assetid | description | |||
|---|---|---|---|---|---|---|---|---|---|
Application Management Overview |
03/30/2017 |
overview |
|
|
32b1c054-5aca-423b-b4b5-ed8dc4dc637d |
Learn about the functionality in the Application class for creating and managing applications in WPF. |
All applications tend to share a common set of functionality that applies to application implementation and management. This topic provides an overview of the functionality in the xref:System.Windows.Application class for creating and managing applications.
In WPF, common application-scoped functionality is encapsulated in the xref:System.Windows.Application class. The xref:System.Windows.Application class includes the following functionality:
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Tracking and interacting with application lifetime.
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Retrieving and processing command-line parameters.
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Detecting and responding to unhandled exceptions.
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Sharing application-scope properties and resources.
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Managing windows in standalone applications.
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Tracking and managing navigation.
If you are not interested in all of the details of the xref:System.Windows.Application class, the following table lists some of the common tasks for xref:System.Windows.Application and how to accomplish them. By viewing the related API and topics, you can find more information and sample code.
| Task | Approach |
|---|---|
| Get an object that represents the current application | Use the xref:System.Windows.Application.Current%2A?displayProperty=nameWithType property. |
| Add a startup screen to an application | See Add a Splash Screen to a WPF Application. |
| Start an application | Use the xref:System.Windows.Application.Run%2A?displayProperty=nameWithType method. |
| Stop an application | Use the xref:System.Windows.Application.Shutdown%2A method of the xref:System.Windows.Application.Current%2A?displayProperty=nameWithType object. |
| Get arguments from the command line | Handle the xref:System.Windows.Application.Startup?displayProperty=nameWithType event and use the xref:System.Windows.StartupEventArgs.Args%2A?displayProperty=nameWithType property. For an example, see the xref:System.Windows.Application.Startup?displayProperty=nameWithType event. |
| Get and set the application exit code | Set the xref:System.Windows.ExitEventArgs.ApplicationExitCode%2A?displayProperty=nameWithType property in the xref:System.Windows.Application.Exit?displayProperty=nameWithType event handler or call the xref:System.Windows.Application.Shutdown%2A method and pass in an integer. |
| Detect and respond to unhandled exceptions | Handle the xref:System.Windows.Application.DispatcherUnhandledException event. |
| Get and set application-scoped resources | Use the xref:System.Windows.Application.Resources%2A?displayProperty=nameWithType property. |
| Use an application-scope resource dictionary | See Use an Application-Scope Resource Dictionary. |
| Get and set application-scoped properties | Use the xref:System.Windows.Application.Properties%2A?displayProperty=nameWithType property. |
| Get and save an application's state | See Persist and Restore Application-Scope Properties Across Application Sessions. |
| Manage non-code data files, including resource files, content files, and site-of-origin files. | See WPF Application Resource, Content, and Data Files. |
| Manage windows in standalone applications | See WPF Windows Overview. |
| Track and manage navigation | See Navigation Overview. |
To utilize the functionality of the xref:System.Windows.Application class, you must implement an application definition. A WPF application definition is a class that derives from xref:System.Windows.Application and is configured with a special MSBuild setting.
A typical WPF application definition is implemented using both markup and code-behind. This allows you to use markup to declaratively set application properties, resources, and register events, while handling events and implementing application-specific behavior in code-behind.
The following example shows how to implement an application definition using both markup and code-behind:
[!code-xamlApplicationSnippets#ApplicationXAML]
[!code-csharpApplicationSnippets#ApplicationCODEBEHIND] [!code-vbApplicationSnippets#ApplicationCODEBEHIND]
To allow a markup file and code-behind file to work together, the following needs to happen:
-
In markup, the
Applicationelement must include thex:Classattribute. When the application is built, the existence ofx:Classin the markup file causes MSBuild to create apartialclass that derives from xref:System.Windows.Application and has the name that is specified by thex:Classattribute. This requires the addition of an XML namespace declaration for the XAML schema (xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"). -
In code-behind, the class must be a
partialclass with the same name that is specified by thex:Classattribute in markup and must derive from xref:System.Windows.Application. This allows the code-behind file to be associated with thepartialclass that is generated for the markup file when the application is built (see Building a WPF Application).
Note
When you create a new WPF Application project or WPF Browser Application project using Visual Studio, an application definition is included by default and is defined using both markup and code-behind.
This code is the minimum that is required to implement an application definition. However, an additional MSBuild configuration needs to be made to the application definition before building and running the application.
Standalone applications and XAML browser applications (XBAPs) require the implementation of a certain level of infrastructure before they can run. The most important part of this infrastructure is the entry point. When an application is launched by a user, the operating system calls the entry point, which is a well-known function for starting applications.
[!INCLUDE xbap-unsupported]
Traditionally, developers have needed to write some or all of this code for themselves, depending on the technology. However, WPF generates this code for you when the markup file of your application definition is configured as an MSBuild ApplicationDefinition item, as shown in the following MSBuild project file:
<Project
DefaultTargets="Build"
xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
...
<ApplicationDefinition Include="App.xaml" />
<Compile Include="App.xaml.cs" />
...
</Project>Because the code-behind file contains code, it is marked as an MSBuild Compile item, as is normal.
The application of these MSBuild configurations to the markup and code-behind files of an application definition causes MSBuild to generate code like the following:
[!code-csharpauto-generated-code] [!code-vbauto-generated-code]
The resulting code augments your application definition with additional infrastructure code, which includes the entry-point method Main. The xref:System.STAThreadAttribute attribute is applied to the Main method to indicate that the main UI thread for the WPF application is an STA thread, which is required for WPF applications. When called, Main creates a new instance of App before calling the InitializeComponent method to register the events and set the properties that are implemented in markup. Because InitializeComponent is generated for you, you don't need to explicitly call InitializeComponent from an application definition like you do for xref:System.Windows.Controls.Page and xref:System.Windows.Window implementations. Finally, the xref:System.Windows.Application.Run%2A method is called to start the application.
Because the functionality of the xref:System.Windows.Application class are shared across an application, there can be only one instance of the xref:System.Windows.Application class per xref:System.AppDomain. To enforce this, the xref:System.Windows.Application class is implemented as a singleton class (see Implementing Singleton in C#), which creates a single instance of itself and provides shared access to it with the staticxref:System.Windows.Application.Current%2A property.
The following code shows how to acquire a reference to the xref:System.Windows.Application object for the current xref:System.AppDomain.
[!code-csharpApplicationManagementOverviewSnippets#GetCurrentAppCODE] [!code-vbApplicationManagementOverviewSnippets#GetCurrentAppCODE]
xref:System.Windows.Application.Current%2A returns a reference to an instance of the xref:System.Windows.Application class. If you want a reference to your xref:System.Windows.Application derived class you must cast the value of the xref:System.Windows.Application.Current%2A property, as shown in the following example.
[!code-csharpApplicationManagementOverviewSnippets#GetSTCurrentAppCODE] [!code-vbApplicationManagementOverviewSnippets#GetSTCurrentAppCODE]
You can inspect the value of xref:System.Windows.Application.Current%2A at any point in the lifetime of an xref:System.Windows.Application object. However, you should be careful. After the xref:System.Windows.Application class is instantiated, there is a period during which the state of the xref:System.Windows.Application object is inconsistent. During this period, xref:System.Windows.Application is performing the various initialization tasks that are required by your code to run, including establishing application infrastructure, setting properties, and registering events. If you try to use the xref:System.Windows.Application object during this period, your code may have unexpected results, particularly if it depends on the various xref:System.Windows.Application properties being set.
When xref:System.Windows.Application completes its initialization work, its lifetime truly begins.
The lifetime of a WPF application is marked by several events that are raised by xref:System.Windows.Application to let you know when your application has started, has been activated and deactivated, and has been shut down.
Starting in the .NET Framework 3.5 SP1, you can specify an image to be used in a startup window, or splash screen. The xref:System.Windows.SplashScreen class makes it easy to display a startup window while your application is loading. The xref:System.Windows.SplashScreen window is created and shown before xref:System.Windows.Application.Run%2A is called. For more information, see Application Startup Time and Add a Splash Screen to a WPF Application.
After xref:System.Windows.Application.Run%2A is called and the application is initialized, the application is ready to run. This moment is signified when the xref:System.Windows.Application.Startup event is raised:
[!code-csharpStartup-event] [!code-vbStartup-event]
At this point in an application's lifetime, the most common thing to do is to show a UI.
Most standalone Windows applications open a xref:System.Windows.Window when they begin running. The xref:System.Windows.Application.Startup event handler is one location from which you can do this, as demonstrated by the following code.
[!code-xamlAppShowWindowHardSnippets#StartupEventMARKUP]
[!code-csharpAppShowWindowHardSnippets#StartupEventCODEBEHIND] [!code-vbAppShowWindowHardSnippets#StartupEventCODEBEHIND]
Note
The first xref:System.Windows.Window to be instantiated in a standalone application becomes the main application window by default. This xref:System.Windows.Window object is referenced by the xref:System.Windows.Application.MainWindow%2A?displayProperty=nameWithType property. The value of the xref:System.Windows.Application.MainWindow%2A property can be changed programmatically if a different window than the first instantiated xref:System.Windows.Window should be the main window.
When an XBAP first starts, it will most likely navigate to a xref:System.Windows.Controls.Page. This is shown in the following code.
[!code-xamlXBAPAppStartupSnippets#StartupXBAPMARKUP]
[!code-csharpXBAPAppStartupSnippets#StartupXBAPCODEBEHIND] [!code-vbXBAPAppStartupSnippets#StartupXBAPCODEBEHIND]
If you handle xref:System.Windows.Application.Startup to only open a xref:System.Windows.Window or navigate to a xref:System.Windows.Controls.Page, you can set the StartupUri attribute in markup instead.
The following example shows how to use the xref:System.Windows.Application.StartupUri%2A from a standalone application to open a xref:System.Windows.Window.
[!code-xamlApplicationManagementOverviewSnippets#OverviewStartupUriMARKUP]
The following example shows how to use xref:System.Windows.Application.StartupUri%2A from an XBAP to navigate to a xref:System.Windows.Controls.Page.
[!code-xamlPageSnippets#XBAPStartupUriMARKUP]
This markup has the same effect as the previous code for opening a window.
Note
For more information on navigation, see Navigation Overview.
You need to handle the xref:System.Windows.Application.Startup event to open a xref:System.Windows.Window if you need to instantiate it using a non-parameterless constructor, or you need to set its properties or subscribe to its events before showing it, or you need to process any command-line arguments that were supplied when the application was launched.
In Windows, standalone applications can be launched from either a command prompt or the desktop. In both cases, command-line arguments can be passed to the application. The following example shows an application that is launched with a single command-line argument, "/StartMinimized":
wpfapplication.exe /StartMinimized
During application initialization, WPF retrieves the command-line arguments from the operating system and passes them to the xref:System.Windows.Application.Startup event handler via the xref:System.Windows.StartupEventArgs.Args%2A property of the xref:System.Windows.StartupEventArgs parameter. You can retrieve and store the command-line arguments using code like the following.
[!code-xamlApplicationStartupSnippets#HandleStartupXAML]
[!code-csharpApplicationStartupSnippets#HandleStartupCODEBEHIND] [!code-vbApplicationStartupSnippets#HandleStartupCODEBEHIND]
The code handles xref:System.Windows.Application.Startup to check whether the /StartMinimized command-line argument was provided; if so, it opens the main window with a xref:System.Windows.WindowState of xref:System.Windows.WindowState.Minimized. Note that because the xref:System.Windows.Window.WindowState%2A property must be set programmatically, the main xref:System.Windows.Window must be opened explicitly in code.
XBAPs cannot retrieve and process command-line arguments because they are launched using ClickOnce deployment (see Deploying a WPF Application). However, they can retrieve and process query string parameters from the URLs that are used to launch them.
Windows allows users to switch between applications. The most common way is to use the ALT+TAB key combination. An application can only be switched to if it has a visible xref:System.Windows.Window that a user can select. The currently selected xref:System.Windows.Window is the active window (also known as the foreground window) and is the xref:System.Windows.Window that receives user input. The application with the active window is the active application (or foreground application). An application becomes the active application in the following circumstances:
-
It is launched and shows a xref:System.Windows.Window.
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A user switches from another application by selecting a xref:System.Windows.Window in the application.
You can detect when an application becomes active by handling the xref:System.Windows.Application.Activated?displayProperty=nameWithType event.
Likewise, an application can become inactive in the following circumstances:
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A user switches to another application from the current one.
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When the application shuts down.
You can detect when an application becomes inactive by handling the xref:System.Windows.Application.Deactivated?displayProperty=nameWithType event.
The following code shows how to handle the xref:System.Windows.Application.Activated and xref:System.Windows.Application.Deactivated events to determine whether an application is active.
[!code-xamlApplicationActivationSnippets#DetectActivationStateXAML]
[!code-csharpApplicationActivationSnippets#DetectActivationStateCODEBEHIND] [!code-vbApplicationActivationSnippets#DetectActivationStateCODEBEHIND]
A xref:System.Windows.Window can also be activated and deactivated. See xref:System.Windows.Window.Activated?displayProperty=nameWithType and xref:System.Windows.Window.Deactivated?displayProperty=nameWithType for more information.
Note
Neither xref:System.Windows.Application.Activated?displayProperty=nameWithType nor xref:System.Windows.Application.Deactivated?displayProperty=nameWithType is raised for XBAPs.
The life of an application ends when it is shut down, which can occur for the following reasons:
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A user closes every xref:System.Windows.Window.
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A user closes the main xref:System.Windows.Window.
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A user ends the Windows session by logging off or shutting down.
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An application-specific condition has been met.
To help you manage application shutdown, xref:System.Windows.Application provides the xref:System.Windows.Application.Shutdown%2A method, the xref:System.Windows.Application.ShutdownMode%2A property, and the xref:System.Windows.Application.SessionEnding and xref:System.Windows.Application.Exit events.
Note
xref:System.Windows.Application.Shutdown%2A can only be called from applications that have xref:System.Security.Permissions.UIPermission. Standalone WPF applications always have this permission. However, XBAPs running in the Internet zone partial-trust security sandbox do not.
Most applications shut down either when all the windows are closed or when the main window is closed. Sometimes, however, other application-specific conditions may determine when an application shuts down. You can specify the conditions under which your application will shut down by setting xref:System.Windows.Application.ShutdownMode%2A with one of the following xref:System.Windows.ShutdownMode enumeration values:
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xref:System.Windows.ShutdownMode.OnLastWindowClose
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xref:System.Windows.ShutdownMode.OnMainWindowClose
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xref:System.Windows.ShutdownMode.OnExplicitShutdown
The default value of xref:System.Windows.Application.ShutdownMode%2A is xref:System.Windows.ShutdownMode.OnLastWindowClose, which means that an application automatically shuts down when the last window in the application is closed by the user. However, if your application should be shut down when the main window is closed, WPF automatically does that if you set xref:System.Windows.Application.ShutdownMode%2A to xref:System.Windows.ShutdownMode.OnMainWindowClose. This is shown in the following example.
[!code-xamlApplicationShutdownModeSnippets#OnMainWindowCloseMARKUP]
When you have application-specific shutdown conditions, you set xref:System.Windows.Application.ShutdownMode%2A to xref:System.Windows.ShutdownMode.OnExplicitShutdown. In this case, it is your responsibility to shut an application down by explicitly calling the xref:System.Windows.Application.Shutdown%2A method; otherwise, your application will continue running even if all the windows are closed. Note that xref:System.Windows.Application.Shutdown%2A is called implicitly when the xref:System.Windows.Application.ShutdownMode%2A is either xref:System.Windows.ShutdownMode.OnLastWindowClose or xref:System.Windows.ShutdownMode.OnMainWindowClose.
Note
xref:System.Windows.Application.ShutdownMode%2A can be set from an XBAP, but it is ignored; an XBAP is always shut down when it is navigated away from in a browser or when the browser that hosts the XBAP is closed. For more information, see Navigation Overview.
The shutdown conditions that are described by the xref:System.Windows.Application.ShutdownMode%2A property are specific to an application. In some cases, though, an application may shut down as a result of an external condition. The most common external condition occurs when a user ends the Windows session by the following actions:
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Logging off
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Shutting down
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Restarting
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Hibernating
To detect when a Windows session ends, you can handle the xref:System.Windows.Application.SessionEnding event, as illustrated in the following example.
[!code-xamlApplicationSessionEndingSnippets#HandlingSessionEndingXAML]
[!code-csharpApplicationSessionEndingSnippets#HandlingSessionEndingCODEBEHIND] [!code-vbApplicationSessionEndingSnippets#HandlingSessionEndingCODEBEHIND]
In this example, the code inspects the xref:System.Windows.SessionEndingCancelEventArgs.ReasonSessionEnding%2A property to determine how the Windows session is ending. It uses this value to display a confirmation message to the user. If the user does not want the session to end, the code sets xref:System.ComponentModel.CancelEventArgs.Cancel%2A to true to prevent the Windows session from ending.
Note
xref:System.Windows.Application.SessionEnding is not raised for XBAPs.
When an application shuts down, it may need to perform some final processing, such as persisting application state. For these situations, you can handle the xref:System.Windows.Application.Exit event, as the App_Exit event handler does in the following example. It is defined as an event handler in the App.xaml file. Its implementation is highlighted in the App.xaml.cs and Application.xaml.vb files.
[!code-xamlDefining-the-Exit-event-handler]
[!code-csharpHandling-the-Exit-event] [!code-vbHandling-the-Exit-event]
For the complete example, see Persist and Restore Application-Scope Properties Across Application Sessions.
xref:System.Windows.Application.Exit can be handled by both standalone applications and XBAPs. For XBAPs, xref:System.Windows.Application.Exit is raised when in the following circumstances:
-
An XBAP is navigated away from.
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In Internet Explorer, when the tab that is hosting the XBAP is closed.
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When the browser is closed.
Applications are mostly launched by the operating system in response to a user request. However, an application can be launched by another application to perform some specific task. When the launched application shuts down, the launching application may want to know the condition under which the launched application shut down. In these situations, Windows allows applications to return an application exit code on shutdown. By default, WPF applications return an exit code value of 0.
Note
When you debug from Visual Studio, the application exit code is displayed in the Output window when the application shuts down, in a message that looks like the following:
The program '[5340] AWPFApp.vshost.exe: Managed' has exited with code 0 (0x0).
You open the Output window by clicking Output on the View menu.
To change the exit code, you can call the xref:System.Windows.Application.Shutdown%28System.Int32%29 overload, which accepts an integer argument to be the exit code:
[!code-csharpApplicationExitSnippets#AppExitCODE] [!code-vbApplicationExitSnippets#AppExitCODE]
You can detect the value of the exit code, and change it, by handling the xref:System.Windows.Application.Exit event. The xref:System.Windows.Application.Exit event handler is passed an xref:System.Windows.ExitEventArgs which provides access to the exit code with the xref:System.Windows.ExitEventArgs.ApplicationExitCode%2A property. For more information, see xref:System.Windows.Application.Exit.
Note
You can set the exit code in both standalone applications and XBAPs. However, the exit code value is ignored for XBAPs.
Sometimes an application may shut down under abnormal conditions, such as when an unanticipated exception is thrown. In this case, the application may not have the code to detect and process the exception. This type of exception is an unhandled exception; a notification similar to that shown in the following figure is displayed before the application is closed.
From the user experience perspective, it is better for an application to avoid this default behavior by doing some or all of the following:
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Displaying user-friendly information.
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Attempting to keep an application running.
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Recording detailed, developer-friendly exception information in the Windows event log.
Implementing this support depends on being able to detect unhandled exceptions, which is what the xref:System.Windows.Application.DispatcherUnhandledException event is raised for.
[!code-xamldetecting-unhandled-exceptions]
[!code-csharpcode-to-detect-unhandled-exceptions] [!code-vbcode-to-detect-unhandled-exceptions]
The xref:System.Windows.Application.DispatcherUnhandledException event handler is passed a xref:System.Windows.Threading.DispatcherUnhandledExceptionEventArgs parameter that contains contextual information regarding the unhandled exception, including the exception itself (xref:System.Windows.Threading.DispatcherUnhandledExceptionEventArgs.Exception%2A?displayProperty=nameWithType). You can use this information to determine how to handle the exception.
When you handle xref:System.Windows.Application.DispatcherUnhandledException, you should set the xref:System.Windows.Threading.DispatcherUnhandledExceptionEventArgs.Handled%2A?displayProperty=nameWithType property to true; otherwise, WPF still considers the exception to be unhandled and reverts to the default behavior described earlier. If an unhandled exception is raised and either the xref:System.Windows.Application.DispatcherUnhandledException event is not handled, or the event is handled and xref:System.Windows.Threading.DispatcherUnhandledExceptionEventArgs.Handled%2A is set to false, the application shuts down immediately. Furthermore, no other xref:System.Windows.Application events are raised. Consequently, you need to handle xref:System.Windows.Application.DispatcherUnhandledException if your application has code that must run before the application shuts down.
Although an application may shut down as a result of an unhandled exception, an application usually shuts down in response to a user request, as discussed in the next section.
Standalone applications and XBAPs don't have exactly the same lifetimes. The following figure illustrates the key events in the lifetime of a standalone application and shows the sequence in which they are raised.
Likewise, the following figure illustrates the key events in the lifetime of an XBAP, and shows the sequence in which they are raised.
