C＃计时器，我可以加快但不能减慢速度

Question

I have a timer event setup and I would like to change how often the timer event happens by reading a number from a text box. If the box is '10' and you click the update button the event would trigger every 10ms then if you changed to '100' and clicked it would happen every 100ms and so on.

When I run the program however, i can speed up the event frequency (eg 100ms to 10ms) but I cannot slow it down (eg 10ms to 100ms). Here is the piece of my code that changes the timer when I click:

    private void TimerButton_Click(object sender, EventArgs e)
    {

        getTime = ImgTimeInterval.Text;
        bool isNumeric = int.TryParse(ImgTimeInterval.Text, out timerMS); //if number place number in timerMS
        label2.Text = isNumeric.ToString();
        if (isNumeric)
        {
            System.Timers.Timer timer = new System.Timers.Timer();
            timer.Enabled = false;
            timer.Interval = timerMS;
            timer.Elapsed += new ElapsedEventHandler(timerEvent);
            timer.AutoReset = true;
            timer.Enabled = true;
        }
    }

    public void timerEvent(object source, System.Timers.ElapsedEventArgs e)
    {
        label1.Text = counter.ToString();
        counter = (counter + 1) % 100;
    }

If anyone knows what I may be doing wrong it would be greatly appreciated.

Answer 1

The problem with this code is, that you create a new Timer each time you click the button. Try to create the timer outside the method. You think it's only goes faster, but instead multiple timers trigger the timerEvent

private System.Timers.Timer _timer;

private void CreateTimer()
{
    _timer = new System.Timers.Timer();
    _timer.Enabled = false;
    _timer.Interval = 100;  // default
    _timer.Elapsed += new ElapsedEventHandler(timerEvent);
    _timer.AutoReset = true;
    _timer.Enabled = true;    
}

private void TimerButton_Click(object sender, EventArgs e)
{
    bool isNumeric = int.TryParse(ImgTimeInterval.Text, out timerMS); //if number place number in timerMS
    label2.Text = isNumeric.ToString();
    if (isNumeric)
    {
        _timer.Interval = timerMS;
    }
}

public void timerEvent(object source, System.Timers.ElapsedEventArgs e)
{
    label1.Text = counter.ToString();
    counter = (counter + 1) % 100;
}

Make sure that the CreateTimer is called in the constructor/formload. Also you can now stop the timer within another button event. With _timer.Enabled = false;

Answer 2

You're always creating a new timer and never stopping the old timer. When you "change" it from 100 to 10 your 100ms timer is still firing every 100 ms, so every 100ms two timers are firing at around the same time.

You need to "remember" the old timer so that you can stop it. Or, better yet, just have only one timer that you change the interval on.

private System.Timers.Timer timer = new System.Timers.Timer();
public Form1()
{
    timer.Enabled = false;
    timer.AutoReset = true;
    timer.Elapsed += timerEvent;
}

private void TimerButton_Click(object sender, EventArgs e)
{
    getTime = ImgTimeInterval.Text;
    bool isNumeric = int.TryParse(ImgTimeInterval.Text, out timerMS); //if number place number in timerMS
    label2.Text = isNumeric.ToString();
    if (isNumeric)
    {
        timer.Interval = timerMS;
        timer.Enabled = true;
    }
}

Answer 3

Well the basic problem is that you're building a new one every time. Make a private timer:

private System.Timers.Timer _timer = new System.Timers.Timer();

and then fix it up when the button is clicked:

if (isNumeric)
{
    _timer.Stop();
    _timer.Interval = timerMS;
    _timer.Start();
}

and then in the .ctor , do this:

_timer.Elapsed += new ElapsedEventHandler(timerEvent);

Now you have a single timer that you are just modifying as the user changes the value in the text box.