Allow certain keyboard strokes / events for disabled control

Question

I have a disabled control. I still want the key down and key up events to get fired off, because I would like to be aware of a certain key.

When I tested this out, it seems like none of the control's events get fired. Any ideas on how to get around this?

Answer 1

Lack of interaction is basic idea of disabling control, it is working as intended.

You might use KeyPreview property of Form and then launch event handlers of your disabled control from Form events.

As usually, there is n+1 ways to achieve what you seek for. So I will present only some of them.

1 - Manipulate Focus. Although easy to implement, it is also volatile as user can manipulate focus as well.

 private void button_KeyDown(object sender, KeyEventArgs e)
 {
    ((Control)sender).Controls.Add(helpBox);
    ((Control)sender).Focus(); // Set focus back to control so its KeyUp will be called
 }
 private void button_KeyUp(object sender, KeyEventArgs e)
 {
    ((Control)sender).Controls.Remove(helpBox);
 }

2 - Multiple calls to same event handler. Yes, it is possible. A bit more complicated and might depend on helpBox control class and/or its events. Possible issues may include multiply fired up event handler, however presented code is safe to use even if such situation will occur.

 private void button_KeyDown(object sender, KeyEventArgs e)
 {
    ((Control)sender).Controls.Add(helpBox);
    helpBox.KeyUp += button_KeyUp; //This will add KeyUp of our hosting button to hosted control, which means that said KeyUp handler can be raised by both helpBox and button
 }
 private void button_KeyUp(object sender, KeyEventArgs e)
 {
    ((Control)sender).Controls.Remove(helpBox);
    helpBox.KeyUp -= button1_KeyUp; // to avoid unnecessary calls event handler can be easily "subtracted" from helpBox
 }

3 - Master control by Form itself by use of KeyPreview set to true, shows controls with "help_" as helpBoxes on controls named .

        private void Form1_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyCode == Keys.F1)
            {
                foreach (Control c in this.Controls)
                {
                    string hName = "help_" + c.Name;
                    Control[] help = this.Controls.Find(hName, true);
                    if (help.Length>0)
                    {
                        c.Controls.Add(help[0]);
                    }
                }
            }
        }

        private void Form1_KeyUp(object sender, KeyEventArgs e)
        {
            if (e.KeyCode == Keys.F1)
            {
                foreach (Control c in this.Controls)
                {
                    string hName = "help_" + c.Name;
                    Control[] help = c.Controls.Find(hName, true);
                    if (help.Length > 0)
                    {
                        c.Controls.Remove(help[0]);
                    }
                }
            }
        }

Note: Control on-screen position depends on its parent position (relative to top-left corner of parent), in other words, by changing parent of control (which happens during Controls.Add) control will change its position.

4 - Draw it by yourself! Manipulating controls is not always best solution, instead you might want to just draw something on control.

private void Form1_KeyDown(object sender, KeyEventArgs e) { button1.Tag = true; button1.Update(); }

    private void Form1_KeyUp(object sender, KeyEventArgs e)
    {
        button1.Tag = false;
        button1.Update();
    }

    // there is no reason to re-draw it constantly, Paint event will be fired when needed
    private void button1_Paint(object sender, PaintEventArgs e)
    {
        // remember that all Tag's start as null
        if (((Control)sender).Tag != null && (bool)((Control)sender).Tag == true)
        {
            // and when needed just paint on control drawing area (also known as Canvas)
            e.Graphics.FillRectangle(Brushes.Red, 0, 0, 100, 100);
            e.Graphics.DrawString("Foo!", ((Control)sender).Font, Brushes.Beige, new PointF(5, 5));
        }
    }

Note: Every Control have Tag property, due to it being of object type you can store in it anything you want. Which makes it universal custom property. In case you wonder about meaning of this property: it have no meaning, it is made to be user-defined.