Restricting the Drag of a WPF Window in Predefined Bounds

Updated on Jun 18, 2025

Environment

Product	UI for WPF
Version	2025.2.521

Description

How to restict the dragging of a WPF Window to a specific bounding rectangle.

Solution

To restrict the dragging of a window, you can add a WndProct hook to the HwndSource of the Window object.

csharp

	private RECT restrictedBounds = new RECT() { Left = 150, Top = 150, Right = 795, Bottom = 577 };
	   
	private void HookWindowHandler(Window window)
	{	
		// note that in order for the PresentationSource.FromVisual() method call to return a HwndSource the Show() method of the window should be already called
		mSource = (HwndSource)PresentationSource.FromVisual(window);
		mSource.AddHook(WndProc);
	}    

	private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
	{
		if (msg == (int)WindowsMessage.WM_MOVING)
		{
			RECT window = (RECT)Marshal.PtrToStructure(lParam, typeof(RECT));
			if (window.Left < restrictedBounds.Left)
			{
				window.Right = window.Right + restrictedBounds.Left - window.Left;
				window.Left = restrictedBounds.Left;
			}
			if (window.Top < restrictedBounds.Top)
			{
				window.Bottom = window.Bottom + restrictedBounds.Top - window.Top;
				window.Top = restrictedBounds.Top;
			}
			if (window.Right >= restrictedBounds.Right)
			{
				window.Left = restrictedBounds.Right - window.Right + window.Left - 1;
				window.Right = restrictedBounds.Right - 1;
			}
			if (window.Bottom >= restrictedBounds.Bottom)
			{
				window.Top = restrictedBounds.Bottom - window.Bottom + window.Top - 1;
				window.Bottom = restrictedBounds.Bottom - 1;
			}
			Marshal.StructureToPtr(window, lParam, true);

			handled = true;
			return new IntPtr(1);
		}

		handled = false;
		return IntPtr.Zero;
	}	

	[StructLayout(LayoutKind.Sequential)]
	struct RECT
	{
		public int Left, Top, Right, Bottom;
	}

	enum WindowsMessage
	{
		WM_MOVING = 0x0216
	}