DispatcherTimer.Start() - Start resets the timer interval

[ghost]

DispatcherTimer.Start() does not reset the timer interval if running.

To reset a running DispatcherTimer interval requires either setting IsEnabled false or calling Stop() before calling Start() to reset the interval.

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[ryanmajidi]

@GrantMeStrength Can you please take a look at this issue?

[GrantMeStrength]

I tested the timer with the following code. I found that the timer does restart if Start is called. It's possible you are creating a new timer rather than calling Start on an existing timer.

public sealed partial class MainPage : Page
{

    DispatcherTimer dispatcherTimer;

    public MainPage()
    {
        dispatcherTimer = new DispatcherTimer();
        dispatcherTimer.Tick += dispatcherTimer_Tick;
        dispatcherTimer.Interval = new TimeSpan(0, 0, 5);

        this.InitializeComponent();
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        mytext.Text = "Button clicked, timer start"; // Every time this is called, another 5 seconds is added.
        dispatcherTimer.Start();
    }

    void dispatcherTimer_Tick(object sender, object e)
    {
        mytext.Text = "TICK";
    }
    }

}

[ghost]

Thanks for looking into this John. Back in July 2019 the problem was real, now I don't even know if it was the same Timer? Must have been a problem with the DeLorean... Cheers

[mrhodel]

This is a problem. I'm using .net 4.8 and a stop is required to reset the interval. Contrary to what the documentation says, Start() does not restart the timer.

[seba30]

I faced the same problem with NET48. I created a timer (with TimeSpan.FromMilliseconds(100)) and call Start on every interrupt of my routine. I also added some Console.WriteLine. The outputs are:

2023-01-28T21:29:58.1773610+01:00: Timer start 1528
2023-01-28T21:29:58.1853053+01:00: Timer start 1528
2023-01-28T21:29:58.1888907+01:00: Timer start 1528
2023-01-28T21:29:58.1919945+01:00: Timer start 1528
2023-01-28T21:29:58.2203149+01:00: Timer start 1528
2023-01-28T21:29:58.2232329+01:00: Timer start 1528
2023-01-28T21:29:58.2262691+01:00: Timer start 1528
2023-01-28T21:29:58.2282532+01:00: Timer start 1528
2023-01-28T21:29:58.2548373+01:00: Timer start 1528
2023-01-28T21:29:58.2608372+01:00: Timer start 1528
2023-01-28T21:29:58.2618571+01:00: Timer start 1528
2023-01-28T21:29:58.2658600+01:00: Timer start 1528
2023-01-28T21:29:58.2688371+01:00: Timer start 1528
2023-01-28T21:29:58.2758410+01:00: Timer done 1528
2023-01-28T21:29:58.2758410+01:00: Timer start 1528
2023-01-28T21:29:58.2803360+01:00: Timer start 1528
2023-01-28T21:29:58.2823150+01:00: Timer start 1528
2023-01-28T21:29:58.3085252+01:00: Timer start 1528
2023-01-28T21:29:58.3144913+01:00: Timer start 1528
2023-01-28T21:29:58.3174925+01:00: Timer start 1528
2023-01-28T21:29:58.3204922+01:00: Timer start 1528
2023-01-28T21:29:58.3244917+01:00: Timer start 1528
2023-01-28T21:29:58.3274919+01:00: Timer start 1528
2023-01-28T21:29:58.3304905+01:00: Timer start 1528
2023-01-28T21:29:58.3324905+01:00: Timer start 1528
2023-01-28T21:29:58.3597377+01:00: Timer start 1528
2023-01-28T21:29:58.3611107+01:00: Timer start 1528
2023-01-28T21:29:58.3631703+01:00: Timer start 1528
2023-01-28T21:29:58.3661776+01:00: Timer start 1528
2023-01-28T21:29:58.3834139+01:00: Timer done 1528
2023-01-28T21:29:58.4093558+01:00: Timer start 1528
2023-01-28T21:29:58.4133555+01:00: Timer start 1528
2023-01-28T21:29:58.4153356+01:00: Timer start 1528
2023-01-28T21:29:58.4173590+01:00: Timer start 1528
2023-01-28T21:29:58.5163189+01:00: Timer done 1528

As you can see, the last Start call is less than 100 ms before the EventHandler is raised ("Timer done").

[HeyFlash]

I can confirm that this is the case on .net 4.7.2.
Contrary to documentation the timer does not restart. No new timer is being created. Calling .Stop() Immediately before .Start resolves the issue.