Cursor.Current vs. this.Cursor

Is there a difference between Cursor.Current and this.Cursor (where this is a WinForm) in .Net? I've always used this.Cursor and have had very good luck with it but I've recently started using CodeRush and just embedded some code in a "Wait Cursor" block and CodeRush used the Cursor.Current property. I've seen on the Internet and at work where other programmers have had some problems with the Cursor.Current property. It just got me to wondering if there is a difference in the two. Thanks in advance.

I did a little test. I have two winforms. I click a button on form1, set the Cursor.Current property to Cursors.WaitCursor and then show form2. The cursor doesn't change on either form. It remains Cursors.Default (pointer) cursor.

If I set this.Cursor to Cursors.WaitCursor in the button click event on form1 and show form2, the wait cursor only shows on form1 and the default cursor is on form2 which is expected. So, I still don't know what Cursor.Current does.

Answers


Windows sends the window that contains the mouse cursor the WM_SETCURSOR message, giving it an opportunity to change the cursor shape. A control like TextBox takes advantage of that, changing the cursor into a I-bar. The Control.Cursor property determines what shape will be used.

The Cursor.Current property changes the shape directly, without waiting for a WM_SETCURSOR response. In most cases, that shape is unlikely to survive for long. As soon as the user moves the mouse, WM_SETCURSOR changes it back to Control.Cursor.

The UseWaitCursor property was added in .NET 2.0 to make it easier to display an hourglass. Unfortunately, it doesn't work very well. It requires a WM_SETCURSOR message to change the shape and that won't happen when you set the property to true and then do something that takes a while. Try this code for example:

private void button1_Click(object sender, EventArgs e) {
  this.UseWaitCursor = true;
  System.Threading.Thread.Sleep(3000);
  this.UseWaitCursor = false;
}

The cursor never changes. To whack that into shape, you'll need to use Cursor.Current as well. Here is a little helper class to make it easy:

using System;
using System.Windows.Forms;

public class HourGlass : IDisposable {
  public HourGlass() {
    Enabled = true;
  }
  public void Dispose() {
    Enabled = false;
  }
  public static bool Enabled {
    get { return Application.UseWaitCursor; }
    set {
      if (value == Application.UseWaitCursor) return;
      Application.UseWaitCursor = value;
      Form f = Form.ActiveForm;
      if (f != null && f.Handle != IntPtr.Zero)   // Send WM_SETCURSOR
        SendMessage(f.Handle, 0x20, f.Handle, (IntPtr)1);
    }
  }
  [System.Runtime.InteropServices.DllImport("user32.dll")]
  private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wp, IntPtr lp);
}

And use it like this:

private void button1_Click(object sender, EventArgs e) {
  using (new HourGlass()) {
    System.Threading.Thread.Sleep(3000);
  }
}

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