NativeWindow.CreateHandle Method (System.Windows.Forms)

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Microsoft Visual Studio 2010/.NET Framework 4

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.NET Framework Class Library

NativeWindow..::.CreateHandle Method

Creates a window and its handle with the specified creation parameters.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)

Syntax

Visual Basic

Public Overridable Sub CreateHandle ( _
    cp As CreateParams _
)

public virtual void CreateHandle(
    CreateParams cp
)

Visual C++

public:
virtual void CreateHandle(
    CreateParams^ cp
)

abstract CreateHandle : 
        cp:CreateParams -> unit 
override CreateHandle : 
        cp:CreateParams -> unit

Parameters

cp: Type: System.Windows.Forms..::.CreateParams
A CreateParams that specifies the creation parameters for this window.

Exceptions

Exception	Condition
OutOfMemoryException	The operating system ran out of resources when trying to create the native window.
Win32Exception	The native Win32 API could not create the specified window.
InvalidOperationException	The handle of the current native window is already assigned; in explanation, the Handle property is not equal to Zero.

Remarks

The cp parameter specifies the values that are passed to the native Win32 CreateWindowEx method to create a window and its handle.

When the ClassName field is not nullNothingnullptra null reference (Nothing in Visual Basic), the newly created window handle inherits from the specified class. For example, if ClassName is set to BUTTON, the newly created window is based on the Win32 BUTTON window class. The Param property of the ClassName object must either be nullNothingnullptra null reference (Nothing in Visual Basic) or reference an instance of a class that was declared as a structure.

This code is an excerpt from the example shown in the NativeWindow class overview. Some code is not shown for the purpose of brevity. See NativeWindow for the whole code listing.

Note
The class name provided is registered with the operating system.

Examples

The following code example demonstrates creating a window with a specific operating system window class name. The example creates a class that inherits from NativeWindow to accomplish this.

The MyNativeWindow class creates a new window with the ClassName set to BUTTON. This creates a Win32 button window. The location and size of the button is set, along with specifying additional window styles. The class demonstrates how to use the CreateHandle method and override the WndProc method to intercept window messages that are received. Although the example looks for the WM_ACTIVATEAPP message, this can be replaced in a real program with window messages specific to the type created.

Note
Some control types send their window messages to the window parent instead of the window. See the Windows Platform SDK for more information.

Visual Basic

' MyNativeWindow class to create a window given a class name.
<System.Security.Permissions.PermissionSetAttribute(System.Security.Permissions.SecurityAction.Demand, Name:="FullTrust")> _
Friend Class MyNativeWindow
    Inherits NativeWindow

    ' Constant values were found in the "windows.h" header file.
    Private Const WS_CHILD As Integer = &H40000000, _
                  WS_VISIBLE As Integer = &H10000000, _
                  WM_ACTIVATEAPP As Integer = &H1C

    Private windowHandle As Integer

    Public Sub New(ByVal parent As Form)

        Dim cp As CreateParams = New CreateParams()

        ' Fill in the CreateParams details.
        cp.Caption = "Click here"
        cp.ClassName = "Button"

        ' Set the position on the form
        cp.X = 100
        cp.Y = 100
        cp.Height = 100
        cp.Width = 100

        ' Specify the form as the parent.
        cp.Parent = parent.Handle

        ' Create as a child of the specified parent
        cp.Style = WS_CHILD Or WS_VISIBLE

        ' Create the actual window
        Me.CreateHandle(cp)
    End Sub

    ' Listen to when the handle changes to keep the variable in sync
    <System.Security.Permissions.PermissionSetAttribute(System.Security.Permissions.SecurityAction.Demand, Name:="FullTrust")> _
    Protected Overrides Sub OnHandleChange()
        windowHandle = Me.Handle.ToInt32()
    End Sub

    <System.Security.Permissions.PermissionSetAttribute(System.Security.Permissions.SecurityAction.Demand, Name:="FullTrust")> _
        Protected Overrides Sub WndProc(ByRef m As Message)
        ' Listen for messages that are sent to the button window. Some messages are sent
        ' to the parent window instead of the button's window.

        Select Case (m.Msg)
            Case WM_ACTIVATEAPP
                ' Do something here in response to messages
        End Select

        MyBase.WndProc(m)
    End Sub

End Class

// MyNativeWindow class to create a window given a class name.
[System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
internal class MyNativeWindow : NativeWindow
{

    // Constant values were found in the "windows.h" header file.
    private const int WS_CHILD = 0x40000000,
                      WS_VISIBLE = 0x10000000,
                      WM_ACTIVATEAPP = 0x001C;

    private int windowHandle;

    public MyNativeWindow(Form parent)
    {

        CreateParams cp = new CreateParams();

        // Fill in the CreateParams details.
        cp.Caption = "Click here";
        cp.ClassName = "Button";

        // Set the position on the form
        cp.X = 100;
        cp.Y = 100;
        cp.Height = 100;
        cp.Width = 100;

        // Specify the form as the parent.
        cp.Parent = parent.Handle;

        // Create as a child of the specified parent
        cp.Style = WS_CHILD | WS_VISIBLE;

        // Create the actual window
        this.CreateHandle(cp);
    }

    // Listen to when the handle changes to keep the variable in sync
    [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
    protected override void OnHandleChange()
    {
        windowHandle = (int)this.Handle;
    }

    [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
    protected override void WndProc(ref Message m)
    {
        // Listen for messages that are sent to the button window. Some messages are sent
        // to the parent window instead of the button's window.

        switch (m.Msg)
        {
            case WM_ACTIVATEAPP:
                // Do something here in response to messages
                break;
        }
        base.WndProc(ref m);
    }
}

Visual C++

// MyNativeWindow class to create a window given a class name.
ref class MyNativeWindow: public NativeWindow
{
private:

   // Constant values were found in the S"windows.h" header file.
   literal int WS_CHILD = 0x40000000,WS_VISIBLE = 0x10000000,WM_ACTIVATEAPP = 0x001C;
   int windowHandle;

public:
   MyNativeWindow( Form^ parent )
   {
      CreateParams^ cp = gcnew CreateParams;

      // Fill in the CreateParams details.
      cp->Caption = "Click here";
      cp->ClassName = "Button";

      // Set the position on the form
      cp->X = 100;
      cp->Y = 100;
      cp->Height = 100;
      cp->Width = 100;

      // Specify the form as the parent.
      cp->Parent = parent->Handle;

      // Create as a child of the specified parent
      cp->Style = WS_CHILD | WS_VISIBLE;

      // Create the actual window
      this->CreateHandle( cp );
   }

protected:

   // Listen to when the handle changes to keep the variable in sync

   virtual void OnHandleChange() override
   {
      windowHandle = (int)this->Handle;
   }

   virtual void WndProc( Message % m ) override
   {
      // Listen for messages that are sent to the button window. Some messages are sent
      // to the parent window instead of the button's window.
      switch ( m.Msg )
      {
         case WM_ACTIVATEAPP:

            // Do something here in response to messages
            break;
      }
      NativeWindow::WndProc( m );
   }
};

Version Information

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

.NET Framework Security

UIPermission
for safe subwindows to call this method. Associated enumeration: UIPermissionWindow..::.SafeSubWindows
UIPermission
to create a top-level window. This permission is only demanded if the window style is not a child or if the window does not have a parent. Associated enumeration: UIPermissionWindow..::.SafeTopLevelWindows

Platforms

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Reference

NativeWindow Class

System.Windows.Forms Namespace