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Graphics.GetHdc Method

Gets the handle to the device context associated with this Graphics.

Namespace:  System.Drawing
Assembly:  System.Drawing (in System.Drawing.dll)
[SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]
public IntPtr GetHdc()

Return Value

Type: System.IntPtr
Handle to the device context associated with this Graphics.

Implements

IDeviceContext.GetHdc()

The device context is a Windows structure based on GDI that defines a set of graphical objects and their associated attributes, as well as the graphical modes that affect output. This method returns that device context with the exception of a font. Because a font is not selected, calls to the FromHdc method using a handle returned from the GetHdc method will fail.

Calls to the GetHdc and ReleaseHdc methods must appear in pairs. During the scope of a GetHdc and ReleaseHdc method pair, you usually make only calls to GDI functions. Calls in that scope made to GDI+ methods of the Graphics that produced the hdc parameter fail with an ObjectBusy error. Also, GDI+ ignores any state changes made to the Graphics of the hdc parameter in subsequent operations.

The following code example is designed for use with Windows Forms, and it requires PaintEventArgs e, which is a parameter of the Paint event handler. The example illustrates calling a Windows GDI function to perform the same task as a GDI+ Graphics method. The code performs the following actions:

  • Defines the interoperability DllImportAttribute attribute for the Windows DLL file gdi32.dll. This DLL contains the desired GDI function.

  • Defines the Rectangle function in that DLL as external.

  • Creates a red pen.

  • With the pen, draws a rectangle to the screen using the GDI+ DrawRectangle method.

  • Defines an internal pointer type variable hdc and sets its value to the handle to the device context of the form.

  • Draws a rectangle to the screen using the GDI Rectangle function.

  • Releases the device context represented by the hdc parameter.

public class GDI
{
    [System.Runtime.InteropServices.DllImport("gdi32.dll")]
    internal static extern bool Rectangle(
       IntPtr hdc,
       int ulCornerX, int ulCornerY,
       int lrCornerX, int lrCornerY);
}

[System.Security.Permissions.SecurityPermission(
System.Security.Permissions.SecurityAction.LinkDemand, Flags = 
System.Security.Permissions.SecurityPermissionFlag.UnmanagedCode)]            
private void GetHdcForGDI1(PaintEventArgs e)
{

    // Create pen.
    Pen redPen = new Pen(Color.Red, 1);

    // Draw rectangle with GDI+.
    e.Graphics.DrawRectangle(redPen, 10, 10, 100, 50);

    // Get handle to device context.
    IntPtr hdc = e.Graphics.GetHdc();

    // Draw rectangle with GDI using default pen.
    GDI.Rectangle(hdc, 10, 70, 110, 120);

    // Release handle to device context.
    e.Graphics.ReleaseHdc(hdc);
}

.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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