How Can I Move The Window Like I Want With WinApi

Question

When I try to drag my window with this the window jumps and flickers around:

protected override void WndProc(ref Message m)
{
    if (m.Msg == WM_MOVE)
    {
        int x = (m.LParam.ToInt32() & 0xffff);
        int y = ((m.LParam.ToInt32() >> 16) & 0xffff);

        if (x < 500)
            Location = new Point(0, y);
        else
            base.WndProc(ref m);
    }
    else
        base.WndProc(ref m);
}

must stop jumping
WM_MOVE, WM_MOVING, WM_WINDOWPOSCHANGING or other move event must continue firing while dragging the window because I want every new position to be checked.
another problem is Location = new Point(0, y); fires another move event (this one should be ignored)

Please help!

Are you simply trying to prevent moving the window by dragging? Where does the window start (are you setting 0,0 at inception)? — DonBoitnott, Jun 06 '13 at 13:24
You are forgetting about the WM_MOVING message. Why this needs to be "winapi" is very unclear, the LocationChanged event works well enough. — Hans Passant, Jun 06 '13 at 13:32
Sounds to me like you should be using [WM_WINDOWPOSCHANGING](http://msdn.microsoft.com/en-us/library/windows/desktop/ms632653(v=vs.85).aspx). You can change the WINDOWPOS structure to modify the window position and/or size. Use Marshal.PtrToStructure() to get it out, and Marshal.StructureToPtr() to put it back; very similar to what I did [here](http://stackoverflow.com/a/16932384/2330053) with WM_GETMINMAXINFO. — Idle_Mind, Jun 06 '13 at 14:56
@Idle_Mind If I modify the windowpos structure that wont fire a move/poschanging event right ? Can you make an answer and help out how to do so (earn points) ? — Bitterblue, Jun 06 '13 at 15:12
The initial move and "snap" will fire a Move() event, but afterwards none would be generated...it would just stick to the spot. — Idle_Mind, Jun 06 '13 at 15:20

score 4 · Accepted Answer · answered Jun 06 '13 at 15:21

Here's an example of using WM_WINDOWPOSCHANGING and modifying the WINDOWPOS structure:

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

    public struct WINDOWPOS
    {
        public IntPtr hwnd;
        public IntPtr hwndInsertAfter;
        public int x;
        public int y;
        public int cx;
        public int cy;
        public uint flags;
    }

    public const int WM_WINDOWPOSCHANGING = 0x46;

    protected override void WndProc(ref Message m)
    {
        switch (m.Msg)
        {
            case WM_WINDOWPOSCHANGING:
                WINDOWPOS wp = (WINDOWPOS)System.Runtime.InteropServices.Marshal.PtrToStructure(m.LParam, typeof(WINDOWPOS));
                if (true) // ... if somecondition ...
                {
                    // modify the location with x,y:
                    wp.x = 0;
                    wp.y = 0;
                }
                System.Runtime.InteropServices.Marshal.StructureToPtr(wp, m.LParam, true);
                break;
        }

        base.WndProc(ref m);
    }

}

DonBoitnott · Answer 2 · 2013-06-06T14:00:06.953

0

This should do what you want:

protected override void WndProc(ref Message message)
{
    const Int32 WM_SYSCOMMAND = 0x0112;
    const Int32 SC_MOVE = 0xF010;

    switch (message.Msg)
    {
        case WM_SYSCOMMAND:
            Int32 command = message.WParam.ToInt32() & 0xfff0;
            if (command == SC_MOVE)
            {
                Left = 0;
                Top = 0;
                return;
            }
            break;
    }

    base.WndProc(ref message);
}

Hans Passant suggested the LocationChanged event, and it can work quite nicely. In this example, the window is frozen at 0, 0 until the mouse pointer gets outside of a 500, 500 box:

private void Form1_LocationChanged(Object sender, EventArgs e)
{
    if (MousePosition.X > 500 || MousePosition.Y > 500)
        Location = MousePosition;
    else
        Location = new Point(0, 0);
}

edited Jun 06 '13 at 14:00

answered Jun 06 '13 at 13:31

DonBoitnott

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This event doesn't fire often only once when you start to move the window. I don't want it to stay at `(0, 0)` ALL the time but to decide when I let it move or keep it at one location. – Bitterblue Jun 06 '13 at 13:43
You've provided nothing to suggest such logic. You must explain that if you'd like it to be part of the answer. – DonBoitnott Jun 06 '13 at 13:44
What is this decision-making process then? What criteria for move versus relocate versus do nothing? Put _that_ in the `if` block and set `Left` and `Top` accordingly. Such as `Left = MousePostion.X` instead of zero. – DonBoitnott Jun 06 '13 at 13:53
Sorry maybe this is a misunderstanding. Note the big edit in the question please. – Bitterblue Jun 06 '13 at 14:14
The misunderstanding is that we don't know what you want it to do. You grab the window, start to move it, you make it jump to `0, 0`...then what? If you don't want it to stay at `0, 0`, then what determines when it _doesn't_ stay put? – DonBoitnott Jun 06 '13 at 14:16
Have you tried a clean form with my `WndProc` above ? Make it `if (true)` and then see what happens! – Bitterblue Jun 06 '13 at 14:24

How Can I Move The Window Like I Want With WinApi

2 Answers2