How can I prevent the keydown event of a form in C# from firing more than once?

According to the official documentation, the KeyDown event on a Windows Forms control occurs only once, but it is easy to demonstrate that the event fires continually aslong as a key is held down:

    private void textBox1_KeyDown(object sender, KeyEventArgs e)
    {
        label1.Text = string.Format("{0}", globalCounter++);
    }

How can you consume the event so that it fires only once?

From stackoverflow

• You can override a ProcessCmdKey method.

• since the multiple occourrence of KeyDown is due to the keyrepeat settings of Windows, I think that you should somehow track the KeyUp event of that key also to know that the key has been released.

• you could use a counter!

• Use KeyUp.

  JannieT : I want an easter-egg like feature to be enabled if the user press and hold down a certain key for more than 5 seconds. So KeyUp is not an option.

  Stevo3000 : @JannieT - Record the time of the keydown, and then process this when the keyup is triggered.

  JannieT : Can you do this without introducing a global (class scope) variable?

  Stevo3000 : I can't offhand think of a way to do this without using a member variable. The functionality could be wrapped up into a class that your form could use to encapsulate the logic behind key presses.

• I'm generally a VB guy, but this seems to work for me as demo code, using the form itself as the input source:

  namespace WindowsFormsApplication1
  {
      public partial class Form1 : Form
      {
          private bool _keyHeld;
          public Form1()
          {
              InitializeComponent();
              this.KeyUp += new KeyEventHandler(Form1_KeyUp);
              this.KeyDown += new KeyEventHandler(Form1_KeyDown);
              this._keyHeld = false;
          }
  
          void Form1_KeyUp(object sender, KeyEventArgs e)
          {
              this._keyHeld = false;
          }
  
          void Form1_KeyDown(object sender, KeyEventArgs e)
          {
              if (!this._keyHeld)
              {
                  this._keyHeld = true;
                  if (this.BackColor == Control.DefaultBackColor)
                  {
                      this.BackColor = Color.Red;
                  }
                  else
                  {
                      this.BackColor = Control.DefaultBackColor;
                  }
              }
              else
              {
                  e.Handled = true;
              }
          }
      }   
  }
  

  I think the logic gets a little sketchy if you're holding down multiple keys at a time, but that seems to only fire the event from the last key that was pressed anyway, so I don't think it becomes an issue.

  I tested this in a TextBox in VB, and it worked fine. Wasn't sure on the inheritance conventions I should follow in c#, so I left it as a straight Form for this answer.

  Apologies for any gross code formatting errors, again, this isn't my usual language.

  JannieT : Thanks Frosty840! Sorry about having to use a global variable, though.