Using Thread.Sleep in Xamarin.Forms

Question

I want to execute the following

MainPage = new ContentPage
{
    Content = new StackLayout
    {
        Children =
        {
            new Button
            {
                Text = "Thread.Sleep",
                Command = new Command(() =>
                {
                    Thread.Sleep(1000);
                    MainPage.Animate("", x => MainPage.BackgroundColor = Color.FromRgb(x, x, x));
                }),
            },
            new Button
            {
                Text = "Task.Run + Thread.Sleep",
                Command = new Command(async () =>
                {
                    await Task.Run(() => Thread.Sleep(1000));
                    MainPage.Animate("", x => MainPage.BackgroundColor = Color.FromRgb(x, x, x));
                })
            },
            new Button
            {
                Text = "Device.StartTimer",
                Command = new Command(() => Device.StartTimer(
                    TimeSpan.FromSeconds(1),
                    () =>
                    {
                        MainPage.Animate("", x => MainPage.BackgroundColor = Color.FromRgb(x, x, x));
                        return false;
                    })),
            },
        }
    }
};

I included System.Threading and System.Threading.Tasks, but I still get

The name 'Thread' does not exist in the current context.

This site suggests that Thread.Sleep can be used in Xamarin.Forms. I have this in a shared project, not a PCL.

`Thread.Sleep` should be avoided while using almost all UI frameworks (WinForms/WPF/Xamarin.Forms/Silverlight/...) as it freezes the UI thread and hangs the UI. — Lex Li, Mar 03 '16 at 12:52
It is only for demonstration purposes, but thanks for your addition. — testing, Mar 03 '16 at 14:30

Sven-Michael Stübe · Accepted Answer · 2017-08-22T07:55:46.310

40

If you want to wait

asynchronously: await Task.Delay(10000);

synchronously: Task.Delay(10000).Wait();

But please try to avoid blocking the UI thread to ensure a good user experience and keep your app responsive.

Using Thread.Sleep in Xamarin.Forms

There are two Xamarin.Forms templates:

Xamarin.Forms Portable Class Library

Because of the PCL subset mechanism, you have no chance to get Thread.Sleep.

Update 2017: PCLs are deprecated, now. If you use .netstandard 2.0, you can use Thread.Sleep as you are used to it.
Xamarin.Forms Shared Project

This Template contains different platforms that do not support Thread.Sleep. Windows UWP, Xamarin.Android and Xamarin.iOS support it, Windows Phone 8.1, and Windows 8.1 not. If you unload/delete the 2 projects, the solution builds. (don't forget using System.Threading; in your App.cs)

edited Aug 22 '17 at 07:55

answered Mar 03 '16 at 09:24

Sven-Michael Stübe

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You are right that the UI thread should not get blocked. Here it is only for demonstration purposes. – testing Mar 03 '16 at 09:24
Do you have an idea why `Thread` isn't recognized? On the linked page it seems that it somehow works. – testing Mar 03 '16 at 09:27
1

I think you don't have `Thread.Sleep` because of a different PCL profile of your Core library. The more supported platforms you select in the PCL, the less supported classes / functions you can use. – Sven-Michael Stübe Mar 03 '16 at 09:35
Any ideas where this can be changed? – testing Mar 03 '16 at 09:37
If you use a `Shared Library` instead of a `Portable Class Library`, it should work. But be aware, that some platforms simply don't support `Thread.Sleep` (e.g. WinPhone 8.1) – Sven-Michael Stübe Mar 03 '16 at 09:39
I tried it in a new `Blank App (Xamarin.Forms Shared)` and I get the same behavior. Strange ... – testing Mar 03 '16 at 09:58
1

This is because the Template contains different platforms that do not support `Thread.Sleep`. Windows UWP, Xamarin.Android and Xamarin.iOS support it, Windows Phone 8.1, and Windows 8.1 not. if you unload/delete the 2 projects, the solution builds. (don't forget `using System.Threading;` in your App.cs. – Sven-Michael Stübe Mar 03 '16 at 10:12
That is the solution. Please edit you answer and I'll give you the tick. – testing Mar 03 '16 at 10:22
I summarized it in the answer. – Sven-Michael Stübe Mar 03 '16 at 10:32

Rahul Tripathi · Answer 2 · 2016-03-03T09:22:48.883

4

You can try to use

await Task.Delay(milliseconds);

if you want to put a delay in your thread.

For blocking you can do

Task.Delay(TimeSpan.FromSeconds(5)).Wait();

edited Mar 03 '16 at 09:22

answered Mar 03 '16 at 09:13

Rahul Tripathi

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You could do that, but that is different from the example I want to try. The thread should get blocked with the first button not delayed. Do you have an idea what I'm missing? A reference in the sub projects? – testing Mar 03 '16 at 09:20
@testing:- Updated my answer to block it. Please check – Rahul Tripathi Mar 03 '16 at 09:23

Using Thread.Sleep in Xamarin.Forms

2 Answers2

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