Change a Window background color, given a IntPtr handle

Question

In c#, I have a handle to a window ( an IntPtr ), I want to change the background color of that window. How can I do this?

I can get the GDI graphics object for that handle like so:

Graphics graphics = Graphics.FromHwnd(theHandle);

So I should somehow be able to change the background color from this?

I also want to ensure the background color remains even after the window moves,resizes,repaints etc.

Answer 1

I think I'm close: My return values are all good, but the window's background color isn't changing. I'm accessing a window created by .NET, (Not C or C++) so the window may be repainting itself through .NET functionality after the native GDI call.

Here's what I have:

---

using System.Runtime.InteropServices;

public class NativeWIN32

{
    [DllImport("gdi32")]
    public static extern int SetBkColor(IntPtr hDC, int crColor); 

}

---

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        IntPtr hWnd = this.Handle;
        Graphics windowGraphics = Graphics.FromHwnd(hWnd);
        IntPtr hdc = windowGraphics.GetHdc();
        int ret = NativeWIN32.SetBkColor(hdc, 0); // Set to black
    }

}

---

Perhaps this will work for a Win32 window, otherwise I hope this helps someone else find the correct solution.

Answer 2

Create a control class with the Control.FromHandle method and then set the property.

Something like...

    Control someControl = Control.FromHandle(myHandle);
    someControl.BackColor = SystemColors.Black;

Answer 3

I don't think there's a way to do this directly with a native (C/C++) window (i.e. there is no native GDI analogue to Control.BackColor).

From looking in Reflector it appears that Control uses the BackColor property to respond to the various WM_CTLCOLOR* messages (e.g. WM_CTLCOLOREDIT). So, if you want to change the background color of a native control, you may need to subclass that window and respond to that same message. If the native window is not a control, you'll still need to subclass the window, but you'd have to handle WM_PAINT or WM_ERASEBKGND instead.

Try this thread on programmersheaven.com for a suggestion on how to subclass a native window from C#.