Why Are Only the Resize Events Triggering in My Custom PictureBox User Control?

A modified version of the original User Control.

What has been changed:

• When WM_NCHITTEST is received and the Mouse pointer is in the Client Area of the window, m.Result is set to HTCLIENT (= 1). The original code was turning this value into HTCAPTION (= 2), to trigger the default functionality of the Mouse when the left Button is down: drag the window. This can be handy in some cases, but other events are not generated anymore when the Mouse pointer is, allegedly, over the Caption of a window. For example, the Click event.

  The code here restores the default behavior, the HTCLIENT location is preserved, the UserControl movement is triggered and calculated using the OnMouseDown and OnMouseMove methods, so all other events are working again

• WM_SETCURSOR is not handled anymore, the Cursor shape is changed when the Mouse is moved while keeping the Left Button pressed

• The UserControl was missing the InitializeComponent() call

• You don't usually subscribe to events of your own derived class, you override the methods that raise the events: e.g., do not subscribe to the Click event, override OnClick etc.

• Do not, ever, load the image from a path in a custom component, especially using an absolute path: when you deploy your component, that path will not exist. While in design mode, the source path of the Visual Studio designer can (will) be something entirely different, so relative paths won't work either (or, are bound to fail, causing an exception in the Designer). Use an Image stored as embedded resource instead.

• Bonus: naming conventions in C# require that the name of a class start with a capital letter. It may not seem that important, but a C# dev that looks at your code may (will) immediately become skeptical, can't avoid thinking that you, quite probably, don't know what you're doing (or you're coming from somewhere else; same thing, different mindset). You may want to avoid this

CSHARPCopied
public class UserControlAddImage : UserControl {

    Point mouseDownPosition = Point.Empty;

    public UserControlAddImage() {
        InitializeComponent();
        BackgroundImage = Properties.Resources.[SomeImageFromResources];
        BackgroundImageLayout = ImageLayout.Zoom;
        BorderStyle = BorderStyle.FixedSingle;
    }

    private void InitializeComponent() {
        SuspendLayout();
        Size = new Size(150, 150);
        ResumeLayout(false);
    }

    protected override CreateParams CreateParams {
        get {
            CreateParams cp = base.CreateParams;
            cp.ExStyle = cp.ExStyle | 0x2000000; // WS_EX_COMPOSITED
            return cp;
        }
    }

    protected override void WndProc(ref Message m) {
        base.WndProc(ref m);

        const int borderWidth = 10;

        if (m.Msg == 0x84) { // WM_NCHITTEST
            var pos = PointToClient(new Point(m.LParam.ToInt32()));
            if (pos.X <= ClientRectangle.Left + borderWidth && pos.Y <= ClientRectangle.Top + borderWidth)
                m.Result = new IntPtr(13); // TOPLEFT
            else if (pos.X >= ClientRectangle.Right - borderWidth && pos.Y <= ClientRectangle.Top + borderWidth)
                m.Result = new IntPtr(14); // TOPRIGHT
            else if (pos.X <= ClientRectangle.Left + borderWidth && pos.Y >= ClientRectangle.Bottom - borderWidth)
                m.Result = new IntPtr(16); // BOTTOMLEFT
            else if (pos.X >= ClientRectangle.Right - borderWidth && pos.Y >= ClientRectangle.Bottom - borderWidth)
                m.Result = new IntPtr(17); // BOTTOMRIGHT
            else if (pos.X <= ClientRectangle.Left + borderWidth)
                m.Result = new IntPtr(10); // LEFT
            else if (pos.Y <= ClientRectangle.Top + borderWidth)
                m.Result = new IntPtr(12); // TOP
            else if (pos.X >= ClientRectangle.Right - borderWidth)
                m.Result = new IntPtr(11); // RIGHT
            else if (pos.Y >= ClientRectangle.Bottom - borderWidth)
                m.Result = new IntPtr(15); // BOTTOM
        }
    }

    protected override void OnMouseDown(MouseEventArgs e) {
        base.OnMouseDown(e);
        if (e.Button != MouseButtons.Left) return;
        mouseDownPosition = e.Location;
    }

    protected override void OnMouseMove(MouseEventArgs e) {
        base.OnMouseMove(e);
        if (e.Button != MouseButtons.Left) return;
        Cursor.Current = Cursors.SizeAll;
        Location = new Point(Location.X + (e.Location.X - mouseDownPosition.X),
                             Location.Y + (e.Location.Y - mouseDownPosition.Y));
    }

    protected override void OnMouseUp(MouseEventArgs e) {
        Cursor.Current = Cursors.Default;
        base.OnMouseUp(e);
    }

    protected override void OnClick(EventArgs e) {
        base.OnClick(e);
        Console.WriteLine("User Control clicked!");
    }

    protected override void OnDoubleClick(EventArgs e) {
        base.OnDoubleClick(e);
        Console.WriteLine("User Control DoubleClick!");
    }

    protected override void OnEnter(EventArgs e) {
        base.OnEnter(e);
        Console.WriteLine("User Control Enter!");
    }

    protected override void OnMouseEnter(EventArgs e) {
        base.OnMouseEnter(e);
        Console.WriteLine("User Control MouseEnter!");
    }

    protected override void OnResize(EventArgs e) {
        base.OnResize(e);
        Console.WriteLine("User Control Resize!");
    }
}