C# how to loop while mouse button is held down

To avoid using threads you can add a Timer component on your form/control and simply enable it on mouse down and disable it on mouse up. Then put the code you would normally put inside the loop in the Timer_Tick event. If you want to use System.Timers.Timer you can use the Timer.Elapsed event instead.

Example (using System.Timers.Timer):

using Timer = System.Timers.Timer;
using System.Timers;
using System.Windows.Forms;//WinForms example
private static Timer loopTimer;
private Button formButton;
public YourForm()
{ 
    //loop timer
    loopTimer = new Timer();
    loopTimer.Interval = 500;/interval in milliseconds
    loopTimer.Enabled = false;
    loopTimer.Elapsed += loopTimerEvent;
    loopTimer.AutoReset = true;
    //form button
    formButton.MouseDown += mouseDownEvent;
    formButton.MouseUp += mouseUpEvent;
}
private static void loopTimerEvent(Object source, ElapsedEventArgs e)
{
    //this does whatever you want to happen while clicking on the button
}
private static void mouseDownEvent(object sender, MouseEventArgs e)
{
    loopTimer.Enabled = true;
}
private static void mouseUpEvent(object sender, MouseEventArgs e)
{
    loopTimer.Enabled = false;
}

You could use a thread to do the counting, and stop the thread when the mouse is released. The following has worked nicely for me:

var b = new Button { Text = "Press me" };

int counter = 0;
Thread countThread = null;
bool stop = false;

b.MouseDown += (s, e) =>
{
    stop = false;
    counter = 0;
    countThread = new Thread(() =>
    {
        while (!stop)
        {
            counter++;
            Thread.Sleep(100);
        }
    });
    countThread.Start();
};

b.MouseUp += (s, e) =>
{
    stop = true;
    countThread.Join();
    MessageBox.Show(counter.ToString());
};

Of course, if you want the event handlers to be methods rather than lambdas, you will have to turn all the variables into fields.

    private void button1_MouseDown(object sender, MouseEventArgs e)
    {
        timer1.Enabled = true;
        timer1.Start();

    }

    private void button1_MouseUp(object sender, MouseEventArgs e)
    {
        timer1.Stop();
    }



    private void timer1_Tick(object sender, EventArgs e)
    {
        numericUpDown1.Value++;

    }