Always increasing size of rectangle with mouse down event?

Question

How do I always increasing size of rectangle with mouse down event?

private void btnPlus_MouseDown(object sender, MouseEventArgs e)
{
    rect.Width = rect.Width + 1;
    rect.Height = (int)(((rect.Width) / 4) * 3);

    label1.Text = rect.Width.ToString();
    label2.Text = rect.Height.ToString();

    pictureBox1.Invalidate();
}

Answer 1

1. On mouse down you start timer
2. On timer tick you run your code.
3. On mouse up you stop timer.

Answer 2

The MouseDown event is being called only once when you click the mouse button, even if you keep your finger on the button.

If you want to keep doing a task while your finger is down on the button, create a new thread in the MouseDown event and kill it in the MouseUp event. In the thread, perform a while loop where you perform the increase:

private Thread _increaseWidthThread;
private Boolean _endThreadFlag;

private void btnPlus_MouseDown(object sender, MouseEventArgs e)
{
    _endThreadFlag = false;
    increaseWidthThread = new Thread(() => IncreaseWidth);
}

private void btnPlus_MouseDown(object sender, MouseEventArgs e)
{
    _endThreadFlag = true;
}

private void IncreaseWidth() {
    while (!_endThreadFlag) {
        this.Invoke((MethodInvoker) delegate {
            rect.Width = rect.Width + 1;
            rect.Height = (int)(((rect.Width) / 4) * 3);

            label1.Text = rect.Width.ToString();
            label2.Text = rect.Height.ToString();

            pictureBox1.Invalidate();
        });
    }
}

I use a flag to indicate to the thread when it should stop and an anonymous method to update the GUI from the thread.

---

EDIT

Instead of using a thread, it is maybe better (and simpler) to use a timer as suggested by Andrey . You will be able to adjust the "sensitivity" of the increase by setting the timer interval.

Assuming you use winforms, that would look like:

private System.Windows.Forms.Timer _timer; 

public ClassConstructor () {
    _timer = new System.Windows.Forms.Timer();
    _timer.Interval = 100;  // Set the "sensitivity"
    _timer.Elapsed += new ElapsedEventHandler(OnTimer);
}

private void btnPlus_MouseDown(object sender, MouseEventArgs e)
{
    timer.Start();
}

private void btnPlus_MouseDown(object sender, MouseEventArgs e)
{
    timer.Stop();
}

private void OnTimer(object sender, ElapsedEventArgs e) {
    rect.Width = rect.Width + 1;
    rect.Height = (int)(((rect.Width) / 4) * 3);

    label1.Text = rect.Width.ToString();
    label2.Text = rect.Height.ToString();

    pictureBox1.Invalidate();
}