ViewDidAppear导致我的标签消失（Xamarin.ios，C＃）

Question

i want to segue to a new View Controller when the countdown timer, here set to 10 seconds, reaches 0 seconds. it does this using the thread logic below. the label usually shows the countdown "10, 9, 8, 7" but since i used ViewDidAppear, it doesnt show. at the end itll flash 0 seconds, and the segue will take place. i need the countdown to show the whole time, and cant figure out how and why its dissapearing

using System.Timers; using System.Threading;

... private System.Timers.Timer mytimer; private int countSeconds;

...

    public override void ViewDidLoad()
    {
        base.ViewDidLoad();

        mytimer = new System.Timers.Timer();
        //Trigger event every second
        mytimer.Interval = 1000;  //1000 = 1 second
        mytimer.Elapsed += OnTimedEvent;
        countSeconds = 10; // 300 seconds           
        mytimer.Enabled = true;
        mytimer.Start();

    }

    private void OnTimedEvent(object sender, ElapsedEventArgs e)
    {

        countSeconds--;
        int seconds = countSeconds % 60;
        int minutes = countSeconds / 60;
        string DHCountdownTime = (countSeconds / 60).ToString() + ":" + (countSeconds % 60).ToString("00");  //to give leading 0. so 9 seconds isnt :9 but :09
        InvokeOnMainThread(() =>
        {
            lblTimer.Text = DHCountdownTime;
        });


        if (countSeconds == 0)
        {
            mytimer.Stop();

        }
    }

...
    public override void ViewDidAppear(bool animated)
    {            
        base.ViewDidAppear(animated);
        Thread.Sleep(countSeconds * 1000);                    
        PerformSegue("DHSegue", this);

...

Answer 1

Your Thread.Sleep is blocking the UI thread:

Thread.Sleep(countSeconds * 1000);             

Use a task (or another thread) in order allow the UI thread to continue to process messages:

await Task.Delay(countSeconds * 1000);