We Keep Coding

DispatcherTimer keeps firing after I've stopped it. C# UWP

I'm having trouble with the following code. I have some code that calls SetTimer() and expects the user to respond before interval is reached (in
millisecs). The calling code inherit these funtions. If the user responds, then StopTimer() is called, info is displayed, StartTimer() is called, and the user is expected to respond again within the interval time period. This continues until the user fails in an answer or takes too long (goes past the interval).
The problem is the timers don't stop. They keep repeating even after I've stopped them, set their Tick event to null (by the -= method), and left its scope. I even get new storage with a new DispatcherTimer (I've done this both using the old one and a new one each time). I can't get the old Timer to go away.
What am I doing wrong?
using Windows.UI.XAML;
public DispatcherTimer GameTimer;
internal void SetTimer(int interval)
{
GameTimer = new DispatcherTimer();
GameTimer.Tick += TimerCallback;
GameTimer.Interval = new TimeSpan(0,0,0,0,interval);
GameTimer.Start();
}
internal void StopTimer()
{
GameTimer.Stop();
try
{
GameTimer.Tick -= TimerCallback;
} catch {}
}
private void TimerCallback(object sender, object e)
{
StopTimer();
// Other code
}
Thanks in advance,
-justin

Try stopping the timer by using the sender object, not the actual public timer object:
private void TimerCallback(object sender, object e) {
(sender as DispatcherTimer).Stop();
// Other code
}

As a workaround, you could do something like:
// in your class
private bool _allowExecution = false;
Then whenever you start the time set _allowExecution = true; and when you stop the timer, simply add _allowExecution = false;
The last thing will be to add a simply boolean condition on your timer execute: if (_allowExecute) //do your stuff here

Because you initialize a new DispatcherTimer everytime call SetTimer(int interval). You must stop the old DispatcherTimer instance before initialize a new one.
internal void SetTimer(int interval)
{
StopTimer();
GameTimer = new DispatcherTimer();
GameTimer.Tick += TimerCallback;
GameTimer.Interval = new TimeSpan(0,0,0,0,interval);
GameTimer.Start();
}
internal void StopTimer()
{
if(GameTimer != null)
{
GameTimer.Stop();
GameTimer.Tick -= TimerCallback;
GameTimer = null;
}
}

Is it possible to get Timer.Tick event after diposing it

I have a question about System.Windows.Forms.Timer. Is it possible to get Tick event after disposing it? For example, if the message is in the message loop and I dispose the timer meanwhile. If it is possible what is the best way to prevent against it. Do you now any good sources explaining it, because I couldn't find anything explaining it. Here is same code explaining my problem:
namespace TestTimer
{
public partial class Form1 : Form
{
ObjectWithTimer obj = null;
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
if(obj != null)
{
obj.Deinit();
obj = null;
}
obj = new ObjectWithTimer();
}
}
public class ObjectWithTimer
{
public Object o = new object();
public Timer timer = new Timer();
bool disposed = false;
public ObjectWithTimer()
{
timer.Interval = 10;
timer.Tick += new EventHandler(timer_Tick);
timer.Enabled = true;
}
public void Deinit()
{
timer.Enabled = false;
timer.Tick -= new EventHandler(timer_Tick);
timer.Dispose();
timer = null;
disposed = true;
}
private void timer_Tick(object sender, EventArgs e)
{
if (disposed)
{
//Is it possible to get here
if (timer.Enabled) return;
}
//doing something
}
}
}

Understanding how timers work can help you feel better about it. They are implemented by the operating system, the underlying winapi call to start a timer is SetTimer(). The OS then posts a notification whenever the timer ticks, you get a WM_TIMER message. The plumbing in Winforms ensures that your Tick event handler runs when this message is received.
These messages are stored in the message queue, an internal data structure associated with a window. This queue serializes messages, it is the basic mechanism that ensures that you for example can never lose a mouse click or a keyboard key press, even when the window is unresponsive because the UI thread is busy with something else.
This queue gives reason to be cautious, what happens when the queue stores a WM_TIMER message when you disposed the timer? Unless something drastic is done, you'd still get that message and your Tick event handler will fire.
But no need to worry, WM_TIMER belongs to a small group of messages that are generated in a special way. They are synthesized messages, it is only ever generated when your program asks for a message with GetMessage(). Other common messages that belong that group are WM_PAINT, it fires the Paint event. Note how you can call Invalidate() as often as you like, you still get only a single Paint event. WM_MOUSEMOVE is another one, it fires the MouseMove event. Something you can reason about, no matter how fast you move the mouse, you can never flood the message queue with mouse-move messages.
Another characteristic of these synthesized messages is that they appear to have a "low priority". Given is that they are only ever synthesized when the message queue is empty. Which is why keyboard messages and mouse clicks always generate an event ahead of a paint.
Long story short, you can only get a WM_TIMER message if you ask for a message and the timer is still alive. The Timer.Dispose() method calls KillTimer() under the hood. Which ends any opportunity to still get a Tick event. Only possible way that could get screwed up is when you call the Stop() or Dispose() methods from a worker thread. Don't do that.

The Windows Forms Timer is single threaded so is not possible that while disposing it you are in timer_Tick.
Also you are not detaching your event in deinit function.

This is very easy to test. I've modified your code a bit:
public class Form1 : Form
{
public Form1()
{
var button = new Button();
button.Click += button1_Click;
Controls.Add(button);
}
private void button1_Click(object sender, EventArgs e)
{
var obj = new ObjectWithTimer();
Thread.Sleep(2000);
obj.Deinit();
}
}
public class ObjectWithTimer
{
public System.Windows.Forms.Timer timer = new System.Windows.Forms.Timer();
bool disposed = false;
public ObjectWithTimer()
{
timer.Interval = 100;
timer.Tick += new EventHandler(timer_Tick);
timer.Enabled = true;
}
public void Deinit()
{
timer.Enabled = false;
timer.Tick -= new EventHandler(timer_Tick);
timer.Dispose();
timer = null;
disposed = true;
}
private void timer_Tick(object sender, EventArgs e)
{
"Ticked".Dump();
}
}
The Thread.Sleep ensures the UI thread is occupied while the timer does its ticking.
The result? No, the Tick will not fire after the timer is disabled. Even the timer.Tick -= new EventHandler(timer_Tick); is unnecessary.

What event is responsible for actions when time is out in Timer Control?

My program is some kind of test. The time of passing test is limited(20 minutes). When the time is out, the test must be finished and MessageBox appears with results of test. In Form_Load :
timer1.Tick += new EventHandler(timer1_Tick);
timer1.Interval = (1000) * (1);
timer1.Enabled = true;
timer1.Start();
private void timer1_Tick(object sender, EventArgs e)
{
timer_label.Text = Convert.ToString(time);
--time;
}
How to finish test when time == 0? And why time in timer_label changes with step 2?(e.g. 1999, 1997, 1995...)

How to finish test when time == 0?
Timer just raises even on some interval. You should start timer for that. If you don't want events to be raised anymore, you should stop timer. You can do it directly in Tick event handler:
private void timer1_Tick(object sender, EventArgs e)
{
timer_label.Text = Convert.ToString(time);
time--;
if (time == 0)
timer1.Stop();
}
Second question:
And why time in timer_label changes with step 2?(e.g. 1999, 1997,
1995...)
From your code there is no reason for such behavior. Looks like you have subscribed to two timers, or you have two event handlers of same timer Tick event. Also make sure you don't have decrement operator when displaying time, something like this:
timer_label.Text = Convert.ToString(--time);
--time;

Timer event handler keeps getting called?

I seem to have a thread issue I think, I have written a timer to return to the main screen if its on any other screen for 5 seconds. This code works fine the first time the ResetScreen() is called, but after it returns to the main screen itself, I can't navigate to any other screen as it keeps returning to the Timer event handler.
I also tested this without the this.Dispatcher.Invoke and replaced it with a message box, and it just constant pops up about every second.
private void ResetScreen()
{
if (!mainScreen)
{
myTimer = new System.Timers.Timer();
myTimer.Elapsed += new ElapsedEventHandler(OnTimedEvent);
myTimer.Interval = 5000;
myTimer.Start();
}
}
private void OnTimedEvent(object source, ElapsedEventArgs e)
{
myTimer.Stop();
this.Dispatcher.Invoke((Action)(() =>
{
// show main screen
}));
}
Edit:
I think its just a timer issue in general. Just can't seem to stop the timer.

When using System.Timers.Timer() you need to explicitly set the AutoReset property to false:
myTimer = new System.Timers.Timer();
myTimer.Elapsed += new ElapsedEventHandler(OnTimedEvent);
myTimer.Interval = 5000;
myTimer.AutoReset = false;
myTimer.Start();
Check out the documentation and examples on MSDN.

How do I show text on a label for a specific time (like 3 seconds)?

I have a statusbar label and I want to show a text on my StatusBar Label for 3 seconds only
How can I do it without using threads?
public void InfoLabel(string value)
{
if (InvokeRequired)
{
this.Invoke(new Action<string>(InfoLabel), new object[] { value });
return;
}
infoLabel.Text = value;
}

Simply add timer on the end of your method:
if (!string.IsNullOrWhiteSpace(value))
{
System.Timers.Timer timer = new System.Timers.Timer(3000) { Enabled = true };
timer.Elapsed += (sender, args) =>
{
this.InfoLabel(string.Empty);
timer.Dispose();
};
}

You need to define a function that you call each time you need to display your text, inside this function you define a timer, this timer is based on System.Windows.Forms.Timer, the only difference is that its modified to hold a stopTime parameter that represents the running duration, the only thing you need to do is to put your starting code(display text) inside the MyFunction function and to put the ending code(to stop displaying text) inside the Timer_Tick function, once you call MyFunction just specify how many seconds you want it to run in the function parameter.
private void MyFunction(int durationInSeconds)
{
MyTimer timer = new MyTimer();
timer.Tick += new EventHandler(Timer_Tick);
timer.Interval = (1000) * (1); // Timer will tick every second, you can change it if you want
timer.Enabled = true;
timer.stopTime = System.DateTime.Now.AddSeconds(durationInSeconds);
timer.Start();
//put your starting code here
}
private void Timer_Tick(object sender, EventArgs e)
{
MyTimer timer = (MyTimer)sender;
if (System.DateTime.Now >= timer.stopTime)
{
timer.Stop();
//put your ending code here
}
}
the modified timer class
public class MyTimer : System.Windows.Forms.Timer
{
public System.DateTime stopTime;
public MyTimer()
{
}
}

You can use Timer to create an instance of a timer that waits for n seconds before firing the Elapsed event. In the elapsed event, you clear the label's Content.
As the timer is executed in a separate thread, the UI thread is not locked while the timer is counting i.e. you are free to perform other operations in the UI.
private delegate void NoArgDelegate();
private void StartTimer(int durationInSeconds)
{
const int milliSecondsPerSecond = 1000;
var timer = new Timer(durationInSeconds * milliSecondsPerSecond);
timer.Start();
timer.Elapsed += timer_Elapsed;
}
private void timer_Elapsed(object sender, ElapsedEventArgs e)
{
var clearLabelTextDelegate = new NoArgDelegate(ClearLabelText);
this.Dispatcher.BeginInvoke(clearLabelTextDelegate);
}
private void ClearLabelText()
{
this.myLabel.Content = string.Empty;
}
As I do not the rest of your code, some suggestions would be to create a lock on the timer so as to prevent more than one UI event starting the timer. In addition, the delegate and the timer instance can be made as private members of the class.

You'll always be using at least the GUI thread. If you decide to wait on that thread, no other interaction with controls is possible (ie. no buttons will work, the window will not be repainted).
Alternatively you could use a System.Windows.Forms.Timer that gives control back to the OS, or another type of timer. Either way, the "countdown" will either block user interaction or happen on another thread (under the hood).