Question

I have a panel whose AutoScroll = true;

I can scroll the panel using scrollbars.

I also find mousewheel “vertical scroll” with “mouse” wheel by writing:

void panelInner_MouseWheel(object sender, System.Windows.Forms.MouseEventArgs e)
{
    panelInner.Focus();
}

However, I want to scroll horizontally by “wheeling mouse + shift” too.

What do I need to do for that to happen?

Answer 1

In your designer file, you’ll need to manually add a MouseWheel event delegate.

this.panelInner.MouseWheel += new System.Windows.Forms.MouseEventHandler(this.panelInner_MouseWheel);

Then, in your code behind, you can add the following.

    private const int WM_SCROLL = 276; // Horizontal scroll 
    private const int SB_LINELEFT = 0; // Scrolls one cell left 
    private const int SB_LINERIGHT = 1; // Scrolls one line right

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    private static extern int SendMessage(IntPtr hWnd, int wMsg, IntPtr wParam, IntPtr lParam); 

    private void panelInner_MouseWheel(object sender, MouseEventArgs e)
    {
        if (ModifierKeys == Keys.Shift)
        {
            var direction = e.Delta > 0 ? SB_LINELEFT : SB_LINERIGHT;

            SendMessage(this.panelInner.Handle, WM_SCROLL, (IntPtr)direction, IntPtr.Zero);
        }
    }

References:

1. Shift + mouse wheel horizontal scrolling
2. Mouse tilt wheel horizontal scrolling in C#