计时器停止后无法启动

Question

In my application I'm using two Timer , each Timer use a BackgroundWorker . Here the declaration:

DispatcherTimer timer1 = new DispatcherTimer(); 
DispatcherTimer timer2 = new DispatcherTimer(); 
BackgroundWorker worker1 = new BackgroundWorker();
BackgroundWorker worker2= new BackgroundWorker(); 

I using timer1 for perform an heavy method with a BackgroundWorker and timer2 for execute another BackgroundWorker that check the content of a file.

In this way I assign the event to BackgroundWorkers :

worker1.DoWork += worker_DoWork;
worker1.RunWorkerCompleted += worker_RunWorkerCompleted;
worker1.WorkerSupportsCancellation = true;
worker2.DoWork += worker_DoWork2;
worker2.RunWorkerCompleted += worker_RunWorkerCompleted2;
worker2.WorkerSupportsCancellation = true;

Now timer1 have a range of 15 minutes so the BackgroundWorker execute the heavy method each 15 minutes. And timer2 have a range of 1 second . With the timer1 all working good, but the problems are coming when I've added the timer2 .

As I said before this timer allow me to start a method that read a file through the worker2 , this file have a property, if this property change I need to perform some special activity. Until here no problem.

What I did is the following:

//This method is called by MainWindow
public ReadFile()
{
    //before this I already assigned to timer1 the tick event and start
    timer2.Tick -= new EventHandler(Event_Tick);
    timer2.Tick += new EventHandler(Event_Tick);
    timer2.Interval = new TimeSpan(0, 0, 1);
    timer2.Start();
}

This is the Tick event associated to timer2

private void Event_Tick(object sender, EventArgs e)
{
     if (!worker1.IsBusy) //I skip the reading, worker1 is busy
     {
         timer1.Stop(); //stop the first timer
         worker2.RunWorkerAsync();
     }
     else
     {
         Console.WriteLine("worker1 is busy!");
     }
 }

I don't need to add here the DoWork , is just a parsing of a file, very useless for the question. When worker2 complete the task I did this:

 private void worker_RunWorkerCompleted2(object sender, RunWorkerCompletedEventArgs e)
{
     timer1.Start();
     ReadFile();
}

How you can see I start the timer1 again, and execute again the ReadFile method. Now if timer1 has reached the interval, so 15 minutes has passed, should execute the timer1.Tick += new EventHandler(Heavy_Tick); that execute the DoWork to worker1 . But the timer1 never start.

I can't figure out to this, what am I doing wrong?

Answer 1

So a lot could be going on here but you should make sure that:

1. You timer isn't storing it's old progress and you are checking for a certain length of time before stopping. This will automatically cause the timer to stop when restarting.

2. The timer.stop() function is not disposing your object to an un-restart-able state.

3. You aren't accessing the timer variable through some pointer that is maintain a stopped value. (Unlikely but annoying when it happens)

I'd personally consider just pausing the timer and resetting the progress, instead of fully stopping it since this is causing issues.

Answer 2

Now I get it! You want to execute worker1 every 15 minutes and worker2 every second but only when worker1 is not busy. Your problem is this here:

if (!worker1.IsBusy) //I skip the reading, worker1 is busy
 {
     timer1.Stop(); //stop the first timer
     worker2.RunWorkerAsync();
 }

and this:

public ReadFile()
{
    //before this I already assigned to timer1 the tick event and start
    timer2.Tick -= new EventHandler(Event_Tick);
    timer2.Tick += new EventHandler(Event_Tick);
    timer2.Interval = new TimeSpan(0, 0, 1);
    timer2.Start();
}

Set both timer intervals and tick event handlers during startup, eg Form_Load() or at the beginning of Main() . Start them there too. You should not have to stop any timer at all! By setting the interval, all you have to do is handle the Tick() event. Remove your .Start() and Stop() calls from your WorkerCompleted and Tick methods and you should do fine.