How to disable a button in c# if a value is false

Question

I'm creating a clipboard editing program and I encountered an error when I use the Copy button. If the text box from where it copies to the clipboard's contents are null, then I get a "ArgumentNullException was not handled". I know this is because the TextBox it copies the text from is empty. I want to write a method where if the TextBox is empty, then the button is disabled. Here is the code for this button:

 // Copies the text in the text box to the clipboard.
    private void copyButton_Click(object sender, EventArgs e)
    {
        Clipboard.SetText(textClipboard.Text);
    }

Any and all help is appreciated. If I'm missing some more details please let me know so I can add them.

Answer 1

You have to initially set the button to be disabled.

Then you can use that code to detect the change in the text box:

    private void textClipboard_TextChanged(object sender, EventArgs e)
    {
        copyButton.Enabled = textClipboard.Text.Length > 0;
    }

Answer 2

You should check for null:

 // Copies the text in the text box to the clipboard.
    private void private void textClipboard_LostFocus(object sender, System.EventArgs e)
    {
        if(!string.IsNullOrEmpty(textClipboard.Text)
        {
            Clipboard.SetText(textClipboard.Text);

        }
        else
        {
          copyButton.Enabled = false; //Set to disabled
        }
    }

Answer 3

You could initially set the button.enabled to false, and add a KeyUp event to your textbox:

    private void textClipboard_KeyUp(object sender, KeyEventArgs e)
    {
        copyButton.Enabled = !string.IsNullOrEmpty(textBox1.Text);
    }