Run code on UI thread in WinRT
.NetMultithreadingWindows 8Windows RuntimeDispatcher.Net Problem Overview
How can I run code on the UI thread in WinRT (Windows 8 Metro)?
The Invoke
method does not exist.
.Net Solutions
Solution 1 - .Net
It's easier to directly get the CoreWindow from the non-UI thread. The following code will work everywhere, even when GetForCurrentThread()
or Window.Current
returns null.
CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal,
<lambda for your code which should run on the UI thread>);
for example:
CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal,
() =>
{
// Your UI update code goes here!
});
You'll need to reference Windows.ApplicationModel.Core
namespace:
using Windows.ApplicationModel.Core;
Solution 2 - .Net
Use:
From your UI thread, execute:
var dispatcher = Windows.UI.Core.CoreWindow.GetForCurrentThread().Dispatcher;
From your background (non UI thread)
dispatcher.RunAsync(DispatcherPriority.Normal,
<lambda for your code which should run on the UI thread>);
That should work on both CP and later builds.
Solution 3 - .Net
Use:
this.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => Frame.Navigate(typeof(Welcome), this));
It works for me.
Solution 4 - .Net
This is a much easier way in my opinion.
Get the TaskScheduler associated with the UI.
var UISyncContext = TaskScheduler.FromCurrentSynchronizationContext();
Then start a new Task and on the above UISyncContext.
Task.Factory.StartNew(() => { /* Do your UI stuff here; */}, new System.Threading.CancellationToken(), TaskCreationOptions.PreferFairness, UISyncContext);
Solution 5 - .Net
DispatcherTimer is also an option.
I used it for code that must be run in Xaml-designer (CoreWindow.Dispatcher,... are not available in UWP-designer)
var localTimer = new DispatcherTimer
{
Interval = TimeSpan.FromMilliseconds(0)
};
localTimer.Tick += (timer, e) =>
{
(timer as DispatcherTimer).Stop();
action();
};
localTimer.Start();
Disclaimer:
I should note that this should be a last-resort option if every other fails.
Solution 6 - .Net
On UWP, I was having problem trying to set the Source property of CaptureElement control (that is defined in XAML), it was complaining about being prepared at different thread, even though I was trying to set it from code that was invoked via a Page_Loaded event handler. I ended up using this to work around it:
previewControl.Dispatcher.TryRunAsync(CoreDispatcherPriority.Normal, () => {
previewControl.Source = _mediaCapture;
}).GetAwaiter().GetResult();