How to: Use a Helper Class for Platform Invokes
This sample program encapsulates the structures, platform invoke declarations, and the delegate for calling native window procedures. The following topics use this class:
How to: Subclass a TreeView by Using Native Callbacks
How to: Subclass a Button by Using Native Callbacks
This example program is described in detail in Subclassing Controls with a Managed Window Procedure.
Example
using System;
using System.Drawing;
using System.Runtime.InteropServices;
// Contains managed wrappers and implementations of Win32
// structures, delegates, constants and platform invokes
// used by the GradientFill and Subclassing samples.
public sealed class Win32
{
public struct TRIVERTEX
{
public int x;
public int y;
public ushort Red;
public ushort Green;
public ushort Blue;
public ushort Alpha;
public TRIVERTEX(int x, int y, Color color)
: this(x, y, color.R, color.G, color.B, color.A)
{
}
public TRIVERTEX(
int x, int y,
ushort red, ushort green, ushort blue,
ushort alpha)
{
this.x = x;
this.y = y;
this.Red = (ushort)(red << 8);
this.Green = (ushort)(green << 8);
this.Blue = (ushort)(blue << 8);
this.Alpha = (ushort)(alpha << 8);
}
}
public struct GRADIENT_RECT
{
public uint UpperLeft;
public uint LowerRight;
public GRADIENT_RECT(uint ul, uint lr)
{
this.UpperLeft = ul;
this.LowerRight = lr;
}
}
public struct GRADIENT_TRIANGLE
{
public uint Vertex1;
public uint Vertex2;
public uint Vertex3;
public GRADIENT_TRIANGLE(uint v1, uint v2, uint v3)
{
this.Vertex1 = v1;
this.Vertex2 = v2;
this.Vertex3 = v3;
}
}
// WM_NOTIFY notification message header.
[System.Runtime.InteropServices.StructLayout(LayoutKind.Sequential)]
public class NMHDR
{
private IntPtr hwndFrom;
public uint idFrom;
public uint code;
}
//[System.Runtime.InteropServices.StructLayout(LayoutKind.Sequential)]
public struct TVITEM
{
public int mask;
private IntPtr hItem;
public int state;
public int stateMask;
private IntPtr pszText;
public int cchTextMax;
public int iImage;
public int iSelectedImage;
public int cChildren;
private IntPtr lParam;
}
// Native representation of a point.
public struct POINT
{
public int X;
public int Y;
}
public struct TVHITTESTINFO
{
public POINT pt;
public uint flags;
private IntPtr hItem;
}
// A callback to a Win32 window procedure (wndproc):
// Parameters:
// hwnd - The handle of the window receiving a message.
// msg - The message
// wParam - The message's parameters (part 1).
// lParam - The message's parameters (part 2).
// Returns an integer as described for the given message in MSDN.
public delegate int WndProc(IntPtr hwnd, uint msg, uint wParam, int lParam);
[DllImport("coredll.dll", SetLastError = true, EntryPoint = "GradientFill")]
public extern static bool GradientFill(
IntPtr hdc,
TRIVERTEX[] pVertex,
uint dwNumVertex,
GRADIENT_RECT[] pMesh,
uint dwNumMesh,
uint dwMode);
public const int GRADIENT_FILL_RECT_H = 0x00000000;
public const int GRADIENT_FILL_RECT_V = 0x00000001;
// Not supported on Windows CE:
public const int GRADIENT_FILL_TRIANGLE = 0x00000002;
[DllImport("coredll.dll")]
public extern static IntPtr SetWindowLong(
IntPtr hwnd, int nIndex, IntPtr dwNewLong);
public const int GWL_WNDPROC = -4;
[DllImport("coredll.dll")]
public extern static int CallWindowProc(
IntPtr lpPrevWndFunc, IntPtr hwnd, uint msg, uint wParam, int lParam);
[DllImport("coredll.dll")]
public extern static int DefWindowProc(
IntPtr hwnd, uint msg, uint wParam, int lParam);
[DllImport("coredll.dll")]
public extern static int SendMessage(
IntPtr hwnd, uint msg, uint wParam, ref TVHITTESTINFO lParam);
[DllImport("coredll.dll", SetLastError = true)]
public extern static int SendMessage(
IntPtr hwnd, uint msg, uint wParam, ref TVITEM lParam);
[DllImport("coredll.dll")]
public extern static uint GetMessagePos();
[DllImport("coredll.dll")]
public extern static IntPtr BeginPaint(IntPtr hwnd, ref PAINTSTRUCT ps);
[DllImport("coredll.dll")]
public extern static bool EndPaint(IntPtr hwnd, ref PAINTSTRUCT ps);
public struct PAINTSTRUCT
{
private IntPtr hdc;
public bool fErase;
public Rectangle rcPaint;
public bool fRestore;
public bool fIncUpdate;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
public byte[] rgbReserved;
}
[DllImport("coredll.dll")]
public extern static IntPtr GetDC(IntPtr hwnd);
[DllImport("coredll.dll")]
public extern static bool ReleaseDC(IntPtr hwnd, IntPtr hdc);
// Helper function to convert a Windows lParam into a Point.
// lParam - The parameter to convert.
// Returns a Point where X is the low 16 bits and Y is the
// high 16 bits of the value passed in.
public static Point LParamToPoint(int lParam)
{
uint ulParam = (uint)lParam;
return new Point(
(int)(ulParam & 0x0000ffff),
(int)((ulParam & 0xffff0000) >> 16));
}
// Windows messages
public const uint WM_PAINT = 0x000F;
public const uint WM_ERASEBKGND = 0x0014;
public const uint WM_KEYDOWN = 0x0100;
public const uint WM_KEYUP = 0x0101;
public const uint WM_MOUSEMOVE = 0x0200;
public const uint WM_LBUTTONDOWN = 0x0201;
public const uint WM_LBUTTONUP = 0x0202;
public const uint WM_NOTIFY = 0x4E;
// Notifications
public const uint NM_CLICK = 0xFFFFFFFE;
public const uint NM_DBLCLK = 0xFFFFFFFD;
public const uint NM_RCLICK = 0xFFFFFFFB;
public const uint NM_RDBLCLK = 0xFFFFFFFA;
// Key
public const uint VK_SPACE = 0x20;
public const uint VK_RETURN = 0x0D;
// Treeview
public const uint TV_FIRST = 0x1100;
public const uint TVM_HITTEST = TV_FIRST + 17;
public const uint TVHT_NOWHERE = 0x0001;
public const uint TVHT_ONITEMICON = 0x0002;
public const uint TVHT_ONITEMLABEL = 0x0004;
public const uint TVHT_ONITEM = (TVHT_ONITEMICON | TVHT_ONITEMLABEL | TVHT_ONITEMSTATEICON);
public const uint TVHT_ONITEMINDENT = 0x0008;
public const uint TVHT_ONITEMBUTTON = 0x0010;
public const uint TVHT_ONITEMRIGHT = 0x0020;
public const uint TVHT_ONITEMSTATEICON = 0x0040;
public const uint TVHT_ABOVE = 0x0100;
public const uint TVHT_BELOW = 0x0200;
public const uint TVHT_TORIGHT = 0x0400;
public const uint TVHT_TOLEFT = 0x0800;
public const uint TVM_GETITEM = TV_FIRST + 62; //TVM_GETITEMW
public const uint TVIF_TEXT = 0x0001;
public const uint TVIF_IMAGE = 0x0002;
public const uint TVIF_PARAM = 0x0004;
public const uint TVIF_STATE = 0x0008;
public const uint TVIF_HANDLE = 0x0010;
public const uint TVIF_SELECTEDIMAGE = 0x0020;
public const uint TVIF_CHILDREN = 0x0040;
public const uint TVIF_DI_SETITEM = 0x1000;
}
See Also
Tasks
How to: Use a Class for Hooking Windows Procedures
How to: Subclass a TreeView by Using Native Callbacks
How to: Subclass a Button by Using Native Callbacks
Concepts
Subclassing Controls with a Managed Window Procedure
.NET Compact Framework How-To Topics