为什么即使分配了null后，Timer仍会触发Elapsed事件

Question

I have a Timer set in my App.cs as follows :

public static void SetSnipDeletingTimer(double d)
{
     TimeBeforeDeletingSpan = new Timer(d) {AutoReset = true, Enabled = true};
     TimeBeforeDeletingSpan.Elapsed += TimeBeforeDeletingSpan_Elapsed;
     TimeBeforeDeletingSpan.Start();
}

static void TimeBeforeDeletingSpan_Elapsed(object sender, ElapsedEventArgs e)
{
     foreach (var t in ListOfCapturesUriPaths) File.Delete(t);
}

In another class and in a certain logic I assign null to it to stop it, I just do this :

App.TimeBeforeDeletingSpan = null;

The problem is that the Elapsed event still get fired everytime the span passes, as shows this screenshot, where the break point is stoping inside the event though the object is null:

How that can be possible ? and what should I do to stop the execution of that event ?

Answer 1

To prevent events that haven't been started yet:

 App.TimeBeforeDeletingSpan.Enabled = false;

To put the object in the dormant state (whatever that means to the object),

App.TimeBeforeDeletingSpan.Dispose();

The reason that assigning null to a field that previously referenced the object doesn't do anything with the object is that the object could be referenced by any other field or variable. Only the garbage collector can find out and only when it runs.

Answer 2

Setting a null reference to an object does not dispose of the given object, if a type implements IDisposable, you'll need to dispose of it manually.

Another thing to keep in mind here is that Timers run on a separate thread, setting it to null won't prevent that thread from continuing to run, as mentioned earlier, you need to ensure that it's being disposed.