How to call OnPaint event from TextBox TextChanged event?


I have a textBox textchanged event:

private void anyTextBox_TextChanged(object sender, EventArgs e) { btnUpload.Enabled = txtHost.TextLength > 0 && txtUploadFile.TextLength > 0; }

And I have a onPaint event:

protected override void OnPaint(PaintEventArgs e) { base.OnPaint(e); Pen penBorder = new Pen(Color.Red, 3); if (btnUpload.Enabled == false) { e.Graphics.DrawRectangle(penBorder, txtHost.Location.X, txtHost.Location.Y, txtHost.Width - 1, txtHost.Height - 1); e.Graphics.DrawRectangle(penBorder, txtUploadFile.Location.X, txtUploadFile.Location.Y, txtUploadFile.Width - 1, txtUploadFile.Height - 1); } }

But now when I type text in one of the textboxes depending which one to remove the red rectangle around it and if both textboxes with text remove the red rectangle around both of them.

The problem is that the OnPaint event is being called only once when I'm running the program.


Use the Control.Invalidate() method to force a control to be redrawn.


Invalidate() marks the control to the current update region of the window which will be repainted when the next WM_PAINT message is received. This can be earlier or later so it may not always have the effect you wish.

Update() sends this WM_PAINT message and also bypasses the message-queque, so you might want to use a combination of Invalidate() and Update() to always get the result you are hoping for.

To make it easier just call Refresh() because this will do Invalidate() and Update() for you synchronously.


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