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    /// On the screen background or on a dividing line between windows (same as HTNOWHERE, except that the DefWindowProc function produces a system beep to indicate an error).

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WM_ENTERSIZEMOVE

0x231

The WM_ENTERSIZEMOVE message is sent one time to a window after it enters the moving or sizing modal loop. The window enters the moving or sizing modal loop when the user clicks the window's title bar or sizing border, or when the window passes the WM_SYSCOMMAND message to the DefWindowProc function and the wParam parameter of the message specifies the SC_MOVE or SC_SIZE value. The operation is complete when DefWindowProc returns.

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WM_EXITSIZEMOVE

0x232

The WM_EXITSIZEMOVE message is sent one time to a window, after it has exited the moving or sizing modal loop. The window enters the moving or sizing modal loop when the user clicks the window's title bar or sizing border, or when the window passes the WM_SYSCOMMAND message to the DefWindowProc function and the wParam parameter of the message specifies the SC_MOVE or SC_SIZE value. The operation is complete when DefWindowProc returns.

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WM_INPUTLANGCHANGE

0x51

The WM_INPUTLANGCHANGE message is sent to the topmost affected window after an application's input language has been changed. You should make any application-specific settings and pass the message to the DefWindowProc function, which passes the message to all first-level child windows. These child windows can pass the message to DefWindowProc to have it pass the message to their child windows, and so on.

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WM_INPUTLANGCHANGEREQUEST

0x50

The WM_INPUTLANGCHANGEREQUEST message is posted to the window with the focus when the user chooses a new input language, either with the hotkey (specified in the Keyboard control panel application) or from the indicator on the system taskbar. An application can accept the change by passing the message to the DefWindowProc function or reject the change (and prevent it from taking place) by returning immediately.

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WM_MOUSEACTIVATE

0x21

The WM_MOUSEACTIVATE message is sent when the cursor is in an inactive window and the user presses a mouse button. The parent window receives this message only if the child window passes it to the DefWindowProc function.

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WM_MOUSEWHEEL

0x20A

The WM_MOUSEWHEEL message is sent to the focus window when the mouse wheel is rotated. The DefWindowProc function propagates the message to the window's parent. There should be no internal forwarding of the message, since DefWindowProc propagates it up the parent chain until it finds a window that processes it.

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WM_MOUSEHWHEEL

0x20E

The WM_MOUSEHWHEEL message is sent to the focus window when the mouse's horizontal scroll wheel is tilted or rotated. The DefWindowProc function propagates the message to the window's parent. There should be no internal forwarding of the message, since DefWindowProc propagates it up the parent chain until it finds a window that processes it.

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    /// The WM_MOUSEACTIVATE message is sent when the cursor is in an inactive window and the user presses a mouse button. The parent window receives this message only if the child window passes it to the DefWindowProc function.

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    /// The WM_INPUTLANGCHANGEREQUEST message is posted to the window with the focus when the user chooses a new input language, either with the hotkey (specified in the Keyboard control panel application) or from the indicator on the system taskbar. An application can accept the change by passing the message to the DefWindowProc function or reject the change (and prevent it from taking place) by returning immediately.

.

    /// The WM_INPUTLANGCHANGE message is sent to the topmost affected window after an application's input language has been changed. You should make any application-specific settings and pass the message to the DefWindowProc function, which passes the message to all first-level child windows. These child windows can pass the message to DefWindowProc to have it pass the message to their child windows, and so on.

.

    /// The WM_MOUSEWHEEL message is sent to the focus window when the mouse wheel is rotated. The DefWindowProc function propagates the message to the window's parent. There should be no internal forwarding of the message, since DefWindowProc propagates it up the parent chain until it finds a window that processes it.

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    /// The WM_MOUSEHWHEEL message is sent to the focus window when the mouse's horizontal scroll wheel is tilted or rotated. The DefWindowProc function propagates the message to the window's parent. There should be no internal forwarding of the message, since DefWindowProc propagates it up the parent chain until it finds a window that processes it.

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    /// The WM_ENTERSIZEMOVE message is sent one time to a window after it enters the moving or sizing modal loop. The window enters the moving or sizing modal loop when the user clicks the window's title bar or sizing border, or when the window passes the WM_SYSCOMMAND message to the DefWindowProc function and the wParam parameter of the message specifies the SC_MOVE or SC_SIZE value. The operation is complete when DefWindowProc returns.

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    /// The WM_EXITSIZEMOVE message is sent one time to a window, after it has exited the moving or sizing modal loop. The window enters the moving or sizing modal loop when the user clicks the window's title bar or sizing border, or when the window passes the WM_SYSCOMMAND message to the DefWindowProc function and the wParam parameter of the message specifies the SC_MOVE or SC_SIZE value. The operation is complete when DefWindowProc returns.

.

    '''The WM_ENTERSIZEMOVE message is sent one time to a window after it enters the moving or sizing modal loop. The window enters the moving or sizing modal loop when the user clicks the window's title bar or sizing border or when the window passes the WM_SYSCOMMAND message to the DefWindowProc function and the wParam parameter of the message specifies the SC_MOVE or SC_SIZE value. The operation is complete when DefWindowProc returns.

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    '''The WM_EXITSIZEMOVE message is sent one time to a window after it has exited the moving or sizing modal loop. The window enters the moving or sizing modal loop when the user clicks the window's title bar or sizing border or when the window passes the WM_SYSCOMMAND message to the DefWindowProc function and the wParam parameter of the message specifies the SC_MOVE or SC_SIZE value. The operation is complete when DefWindowProc returns.

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    '''The WM_INPUTLANGCHANGE message is sent to the topmost affected window after an application's input language has been changed. You should make any application-specific settings and pass the message to the DefWindowProc function which passes the message to all first-level child windows. These child windows can pass the message to DefWindowProc to have it pass the message to their child windows and so on.

.

    '''The WM_INPUTLANGCHANGEREQUEST message is posted to the window with the focus when the user chooses a new input language either with the hotkey (specified in the Keyboard control panel application) or from the indicator on the system taskbar. An application can accept the change by passing the message to the DefWindowProc function or reject the change (and prevent it from taking place) by returning immediately.

.

    '''The WM_MOUSEACTIVATE message is sent when the cursor is in an inactive window and the user presses a mouse button. The parent window receives this message only if the child window passes it to the DefWindowProc function.

.

    '''The WM_MOUSEWHEEL message is sent to the focus window when the mouse wheel is rotated. The DefWindowProc function propagates the message to the window's parent. There should be no internal forwarding of the message since DefWindowProc propagates it up the parent chain until it finds a window that processes it.

.

    '''The WM_MOUSEHWHEEL message is sent to the focus window when the mouse's horizontal scroll wheel is tilted or rotated. The DefWindowProc function propagates the message to the window's parent. There should be no internal forwarding of the message since DefWindowProc propagates it up the parent chain until it finds a window that processes it.

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    ''' The hit-test value returned by the <c>DefWindowProc</c> function as a

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    ''' The hit-test value returned by the <c>DefWindowProc</c> function as a

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    ''' The hit-test value returned by the <c>DefWindowProc</c> function as a

.

    ''' The hit-test value returned by the <c>DefWindowProc</c> function as a

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    ''' <c>DefWindowProc</c> function and the <paramref name="wParam"/> parameter of the message

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    ''' The operation is complete when <c>DefWindowProc</c> returns.

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    ''' <c>DefWindowProc</c> function and the <paramref name="wParam"/> parameter of the message

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    ''' The operation is complete when <c>DefWindowProc</c> returns.

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    ''' The hit-test value returned by the <c>DefWindowProc</c> function

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    ''' The parent window receives this message only if the child window passes it to the <c>DefWindowProc</c> function.

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    ''' The <c>DefWindowProc</c> function propagates the message to the window's parent.

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    ''' There should be no internal forwarding of the message since <c>DefWindowProc</c> propagates it up the

.

    ''' The <c>DefWindowProc</c> function propagates the message to the window's parent.

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    ''' There should be no internal forwarding of the message since <c>DefWindowProc</c> propagates it up

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    ''' <c>DefWindowProc</c> function from processing the <see cref="WmNchitTest"/> message.

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    ''' <c>DefWindowProc</c> function from processing the <see cref="WmNchitTest"/> message.

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    ''' <c>DefWindowProc</c> function from processing the <see cref="WmNchitTest"/> message.

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When you call this function, the WndProc function must respond to the WM_NCCREATE message by returning TRUE. If it does not, the creation process will fail. A null handle will be returned from CreateWindowEx and GetLastError will return 0. See MSDN on WM_NCCREATE (http://msdn.microsoft.com/en-us/library/ms632635.aspx) and also WM_CREATE (http://msdn.microsoft.com/en-us/library/ms632619.aspx). You can have your WndProc call DefWindowProc, which will take care of this issue.

.

                return Win32.DefWindowProc(hWnd, (WM)message, wParam, lParam);

.

Summary

The DefWindowProc API

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static extern IntPtr DefWindowProc(IntPtr hWnd, WindowsMessages uMsg, IntPtr wParam, IntPtr lParam);

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Public Shared Function DefWindowProc(ByVal hWnd As IntPtr, ByVal uMsg As WindowsMessages, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As IntPtr

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Documentation

[DefWindowProc] on MSDN

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static extern bool DwmDefWindowProc(IntPtr hWnd, int msg, IntPtr wParam, IntPtr lParam, ref IntPtr plResult);

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Private Shared Function DwmDefWindowProc(ByVal hWnd As IntPtr, ByVal msg As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr, ByRef plResult As IntPtr) As Integer

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Documentation

[DwmDefWindowProc] on MSDN