HwndSource Class

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An HwndSource implements a Win32 window that can contain WPF content. The WPF content in the window is arranged, measured, and rendered; and is interactive to input. Because the HwndSource is specifically designed to interoperate with Win32, this class exposes several low-level Win32 features. You can use this class to do the following:

• Specify window styles, window class styles, and extended window styles.

• Hook the window procedure.

• Provide access to the window handle (HWND).

• Destroy the window.

The HwndSource class is designed for general interoperability and is not designed as a managed HWND wrapper. In general, it does not provide managed methods for manipulating the window or properties for inspecting its state. Instead, the HwndSource class provides access to the Win32 window handle (HWND) through the Handle property, which can be passed by means of PInvoke techniques to Win32 APIs in order to manipulate the window.

Construction

Many aspects of the HwndSource can only be specified at construction time. To create an HwndSource, first create an HwndSourceParameters structure and populate it with the desired parameters. These parameters include the following:

• The class, window, and extended window styles. You must use PInvoke to change the styles after the window is created. Not all styles can be changed after the window is created. Consult the Win32 documentation before changing window styles.

• The initial position of the window.

• The initial size of the window, which includes whether the size is specified or should be determined from the determined size of the WPF content.

• The parent window.

• The HwndSourceHook to include in the window procedure chain. If you specify a hook at construction time, it receives all messages for the window. You can use AddHook to add a hook after the window is created.

• The transparency settings. A top-level window can be configured to blend with the other windows on the desktop according to the per-pixel transparency of the WPF content. To enable this, set the UsesPerPixelOpacity property in the HwndSourceParameters to true. This property can only be specified at construction time, and only through the HwndSource(HwndSourceParameters) constructor signature, and it imposes several limitations.

After you populate the HwndSourceParameters structure, pass it to the HwndSource(HwndSourceParameters) constructor for the HwndSource.

Object Lifetime

An HwndSource is a regular common language runtime (CLR) object, and its lifetime is managed by the garbage collector. Because the HwndSource represents an unmanaged resource, HwndSource implements IDisposable. Synchronously calling Dispose immediately destroys the Win32 window if called from the owner thread. If called from another thread, the Win32 window is destroyed asynchronously. Calling Dispose explicitly from the interoperating code might be necessary for certain interoperation scenarios.

Window Procedures

The HwndSource class implements its own window procedure. This window procedure is used to process important window messages, such as those related to layout, rendering, and input. However, you can also hook the window procedure for your own use. You can specify your own hook during construction by setting the HwndSourceParameters.HwndSourceHook property, or you can also use AddHook and RemoveHook to add and remove hooks after the window is created. The hooks are called by last-in first-out order, which enables your hooks to execute before the built-in processing. The actual hooks are held by a weak reference. Therefore, make sure that you manage the lifetime of your hook delegate.

For more information about HwndSource and other interoperation classes, see WPF and Win32 Interoperation.

Notice how the constructors for HwndSource take parameters that resemble the parameters for Win32 functions such as CreateWindowEx.

Scale transformations should not be applied to the RootVisual of an HwndSource. See Remarks for RootVisual.

.NET Framework

.NET Framework Client Profile

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

Other Resources