Custom paint Splitter control in C# WinForms

Question

I am trying to paint the split line that appears when you drag a splitter control:

As you can see from this image, the default splitter is a checkerboard.

...this doesn't work:

public partial class MockForm : Form
{
    public MockForm()
    {
        InitializeComponent();
        this.splitter1.Paint += splitter1_Paint;
    }

    private void splitter1_Paint(object sender, PaintEventArgs e)
    {
        e.Graphics.Clear(Color.Red);
    }
}

this just paints the background of the control but not the splitter when it's dragged.

Any ideas?

Answer 1

The answer posted by LarsTech is really good, But the handler flickers are somehow annoying. Instead of showing the control in Form, if you show a Form as splitter handler and show it above the Container of splitter, the flickers will be gone.

HighLight f = new HighLight() { BackColor = Color.Red };
private void splitter1_SplitterMoving(object sender, SplitterEventArgs e)
{
    this.splitter1.Parent.Refresh();
    f.Location = this.splitter1.Parent.PointToScreen(new Point(e.SplitX, e.SplitY));
    f.Size = this.splitter1.Size;
    if (!f.Visible)
        f.ShowInactiveTopmost();
}
private void splitter1_SplitterMoved(object sender, SplitterEventArgs e)
{
    f.Hide();
}

Here is the form which I used as highlight:

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;
public class HighLight : Form
{
    public HighLight()
    {
        Opacity = 0;
        FormBorderStyle = FormBorderStyle.None;
        ShowInTaskbar = false;
        StartPosition = FormStartPosition.Manual;
    }
    protected override void OnDeactivate(EventArgs e)
    {
        base.OnDeactivate(e);
        this.Hide();
    }
    private const int SW_SHOWNOACTIVATE = 4;
    private const int HWND_TOPMOST = -1;
    private const uint SWP_NOACTIVATE = 0x0010; 
    [DllImport("user32.dll", EntryPoint = "SetWindowPos")]
    static extern bool SetWindowPos(int hWnd, int hWndInsertAfter,
         int X, int Y, int cx, int cy, uint uFlags);
    [DllImport("user32.dll")]
    static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
    public void ShowInactiveTopmost()
    {
        ShowWindow(this.Handle, SW_SHOWNOACTIVATE);
        SetWindowPos(this.Handle.ToInt32(), HWND_TOPMOST,
        this.Left, this.Top, this.Width, this.Height,
        SWP_NOACTIVATE);
        this.Opacity = 1;
    }
}

To see a custom splitter which supports transparent handler take a look at this related post. In the other post I created a new splitter control using source codes of original splitter, but changed rendering the highlight:

• Change Splitter Highlighting/Resize Line