Navigate a keypad in winform using arrow keys

Question

I'm currently working on a personal project and i have a bit of an issue. In the keypad display i ma unable to navigate up and down. Pressing the arrow keys only follows the button tabindex rather than the direction of the arrow key. For example: if i press the down arrow, instead of changing focus to button4, the focus moves to button2.
Although i have come up with some code that works, it does introduce a new problem. The OK button is initially hidden (until there have been 4 key presses), however in my code not only is the focus changed to it, it is also accessible through the keyboard. My question is: Is there a more elegant or efficient way of manipulating which button is focused?
Thank you.
(If it is of any help, i'm using visual studio 2008, C#, .NET3.5)

So far i have come up with this code:

private void frm_Login_KeyDown(object sender, KeyEventArgs e)
{
Control[] MyButtons = new Control[]{b1,b2,b3,b4,b5,b6,b7,b8,b9,btn_OK,b0,btn_Cancel};
switch (e.KeyValue)
{
case 13: //return
{ e.Handled = false; break; }
case 39: //Right
{
if (IndexofFocussedButton < 11) { IndexofFocussedButton++; }
else { IndexofFocussedButton = 0; }
break;
}
case 38: //Up
{
if (IndexofFocussedButton > 2) { IndexofFocussedButton-=3; }
else { IndexofFocussedButton +=9; }
break;
}
case 37: //Left
{
if (IndexofFocussedButton != 0) { IndexofFocussedButton--; }
else { IndexofFocussedButton=11; }
}
break;
case 40: //Down
{
if (IndexofFocussedButton < 9) { IndexofFocussedButton +=3; }
else { IndexofFocussedButton-=9; }
break;
}

}

if (e.KeyValue != 13)
{
e.Handled = true; //Don't pass on the keystroke
MyButtons[IndexofFocussedButton].Focus(); // Set the focus to the selected control
Application.DoEvents();
}

Vulpes · Answer

Your override looks OK to me and should have the same effect as handling the form's PreviewKeyDown event as I did in my previous post. I suspect the problem here is that you should be doing all this for the buttons themselves rather than the form even though the form is handling the KeyDown event first as your code currently stands. To override the IsInputKey method for the buttons you'd need to use a 'custom' button class which inherits from Button which is messy though you could avoid this by handling the PreviewKeyDown event for the 'standard' buttons. What I'd be inclined to do is to handle the KeyDown and PreviewKey for the buttons themselves rather than intercept them at form level. You could of course use the same handler for all the buttons and determine which one has been clicked by replacing this code: Button b = Form.ActiveControl as Button; if (b == null) return; with: Button b = (Button)sender;

Vulpes · Answer

It sounds like you haven't overridden the IsInputKey method for the arrow keys which you need to do for these keys to raise the KeyDown event. In addition to the existing code try handling the Form's PreviewKeyDown event (add the handler from the designer) as follows: private void frm_Login_PreviewKeyDown(object sender PreviewKeyDownEventArgs e) { switch (e.KeyCode) { case Keys.Left: case Keys.Right case Keys.Up: case Keys.Down: { e.IsInputKey = true; break; } } }

Vulpes · Answer

Although it's a bit more work initially what I'd be inclined to do is to associate an array of 4 buttons with each of your buttons where (say) index 0 is left 1 is right 2 is up and 3 is down. If you don't want an arrow key to do anything for a particular button just set the corresponding element in the array to null. After 4 key presses you'd need to change the arrays to bring the OK button into play. You could use a Dictionary to make the assocation. For example: private Dictionary dict; // in Form_Load say dict = new Dictionary (); dict.Add(b1 new Button[]{null b2 b4 b0}; dict.Add(b5 new Button[]{b4 b6 b8 b2}; // and so on for each button except (initially) btn_OK You could then recode the KeyDown handler as follows: int keyPresses = 0; private void frm_Login_KeyDown(object sender KeyEventArgs e) { Button b = Form.ActiveControl as Button; if (b == null) return; keyPresses++; if (keyPresses == 4) { btn_OK.Visible = true; // call method to change the arrays } switch (e.KeyValue) { case 13: //return { e.Handled = false; break; } case 39: //Right { if (dict[b][1] != null) dict[b][1].Focus(); break; } case 38: //Up { if (dict[b][2] != null) dict[b][2].Focus(); break; } case 37: //Left { if (dict[b][0] != null) dict[b][0].Focus(); break; } case 40: //Down { if (dict[b][3] != null) dict[b][3].Focus(); break; } } if (e.KeyValue != 13) { e.Handled = true; Application.DoEvents(); // if needed } }

Stefan Cazacu · Answer

Still no luck. I've tried following your advice and added an override for IsInputKey. I'm thinking either there is something wrong with my override or i didn't place it in the right area. I put it in the form class and the code is: protected override bool IsInputKey(Keys keyData) { if ((keyData == Keys.Left)||(keyData == Keys.Right)|| (keyData == Keys.Up)||(keyData == Keys.Down)) { return true; } else { return base.IsInputKey(keyData); } }

Stefan Cazacu · Answer

I had a hunch that might be it. I tried the code this morning however the focus still changes depending on the tabindex and i haven't managed to figure it out..

Vulpes · Answer

Sorry ActiveControl is an instance property rather than a static property of the Form class so this line is wrong: Button b = Form.ActiveControl as Button; It should be: Button b = this.ActiveControl as Button;

Stefan Cazacu · Answer

Thank you for the answer. I'm rather new at C# and if you could help me a bit more i would be very grateful. I get an error for ActiveControl: An object reference is required for the non static field method or property. Any idea what I'm missing?