如何在计算器Windows窗体应用程序中正确使用ProcessCmdKey？

Question

I'm trying to build a normal calculator in C# Windows Form Application. I want that when I press any numpad key the number will display in the Textbox, like happens in any standard calculator.

So from researching I get this can be done by overriding ProcessCmdKey and changing KeyPreview property of Form to true .

But the problem is : When I entirely work with numpad the calculator works fine. But when I combine mouse-clicking any number button and then try to again use numpad-keys the number doesn't show up in TextBox.

I have a generic on-click method for number button (it will fire for 0-9 all button click)

private void number_button_Click(object sender, EventArgs e)
{
    Button button = (Button)sender;
    textBox1.Text = textBox1.Text + "" + button.Text;
}

Add method (like wise method for subtraction, division, multiplication)

private void buttonPlusClk_Click(object sender, EventArgs e)
{
    sign = "+";
    operandOne = double.Parse(textBox1.Text);
    textBox1.Text = "";
}

For Form

this.KeyPreview = true;

The overridden ProcessCmdKey method

protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
{
    if (keyData == (Keys.NumPad0 |
        Keys.NumPad1 |
        Keys.NumPad2 |
        Keys.NumPad3 |
        Keys.NumPad4 |
        Keys.NumPad5 |
        Keys.NumPad6 |
        Keys.NumPad7 |
        Keys.NumPad8 |
        Keys.NumPad9))
    {

        // also not sure about the KeyEventArgs(keyData)... is it ok?
        number_button_Click(keyData, new KeyEventArgs(keyData));
        return true;

    }
    else if(keyData == (Keys.Add))
    {
        buttonPlusClk_Click(keyData, new KeyEventArgs(keyData));
        return true;
    }
    // ... and the if conditions for other operators
    return base.ProcessCmdKey(ref msg, keyData);
}

Ask me if you want any other code to see.

---

For future reference get the SSCCE from GitHub and to recreate the problem do this

1. Press 2 from keyboard numpad
2. Click +
3. Press 1 from keyboard numpad (You will not see 1 coming in textbox)
4. Click equals

Answer 1

Try this in your key handling function. XOR'ing numbers is incorrect when they are not used as flags.
Also, calling the event handler from this function would result in an error because the first arg is not a button.

        protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
        {
            int intKey = (int)keyData;
            if (intKey >= 96 && intKey <= 105) // 96 = 0, 97 = 1, ..., 105 = 9
            {
                textBox1.Text = textBox1.Text + (intKey - 96).ToString();
                return true;

            }
            // ... and the if conditions for other operators
            return base.ProcessCmdKey(ref msg, keyData);
        }