Question

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Vertically (only) resizable windows form in C#

I have a case where I need to allow the user to resize the form just horizontally. The maximum width of the form is x. How can I do that?

Answer 1

Set your MaximumSize and MinimumSize to the same Height, but variable widths.

To make it so the resize cursor doesn’t appear on the top or bottom:

protected override void WndProc(ref Message m) {
    base.WndProc(ref m);
    switch (m.Msg) {
        case 0x84: //WM_NCHITTEST
            var result = (HitTest)m.Result.ToInt32();
            if (result == HitTest.Top || result == HitTest.Bottom)
                m.Result = new IntPtr((int)HitTest.Caption);
            if (result == HitTest.TopLeft || result == HitTest.BottomLeft)
                m.Result = new IntPtr((int)HitTest.Left);
            if (result == HitTest.TopRight || result == HitTest.BottomRight)
                m.Result = new IntPtr((int)HitTest.Right);

            break;
    }
}
enum HitTest {
    Caption = 2,
    Transparent = -1,
    Nowhere = 0,
    Client = 1,
    Left = 10,
    Right = 11,
    Top = 12,
    TopLeft = 13,
    TopRight = 14,
    Bottom = 15,
    BottomLeft = 16,
    BottomRight = 17,
    Border = 18
}

Code copied and modified from: Vertically (only) resizable windows form in C#