C# Signature:

[DllImport("user32.dll")]
static extern bool InvalidateRect(IntPtr hWnd, IntPtr lpRect, bool bErase);

VB Signature:

Public Overloads Declare Function InvalidateRect Lib "User32" Alias "InvalidateRect" (ByVal hWnd As Int32, ByRef lpRect As RECT, ByVal bErase As Boolean) As Boolean
Public Overloads Declare Function InvalidateRect Lib "User32" Alias "InvalidateRect" (ByVal hWnd As Int32, ByVal lpRect As IntPtr, ByVal bErase As Boolean) As Boolean
Public Overloads Shared Function InvalidateRect(ByVal hWnd As Int32, ByVal bErase As Boolean) As Boolean
     Return InvalidateRect(hWnd, IntPtr.Zero, bErase)
End Function
Public Overloads Shared Function InvalidateRect(ByVal hWnd As Int32, ByVal lpRect As System.Drawing.Rectangle, ByVal bErase As Boolean) As Boolean
     Return InvalidateRect(hWnd, RECT.FromRectangle(lpRect), bErase)
End Function

User-Defined Types:

RECT

Notes:

Useful to force a redraw when you don't have control of the area, when using WindowFromPoint() for example. If you do have control of the object, you can called the managed Control.Invalidate()

Tips & Tricks:

Setting the second param (lpRect) to Int32.Zero will redraw the whole client area.

Sample Code:

/**

POINT and RECT structures are defined elsewhere

you've gotten the rectangle (RECT) you wish to highlight

**/

POINT pt;

RECT rct;

/* converted coords */

Rectangle R;

/* get current current cursor location */

GetCursorPos(out pt)

/* get the window handle */

IntPtr hWnd = WindowFromPoint(pt);

GetWindowRect(hWnd, out rct);

/* draw a red border around your rectangle */

ControlPaint.DrawBorder(System.Drawing.Graphics.FromHwnd(hWnd), R, Color.Red, ButtonBorderStyle.Solid);

/* when you want to clear this rectangle, use this */

InvalidateRect(hWnd, IntPtr.Zero, true);

Alternative Managed API:

Do you know one? Please contribute it!