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using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;
namespace Xamarin.PropertyEditing
{
internal sealed class AsyncValue<T>
: INotifyPropertyChanged
{
public AsyncValue (Task<T> task, T defaultValue = default(T), TaskScheduler scheduler = null)
{
if (task == null)
throw new ArgumentNullException (nameof(task));
this.task = task;
this.defaultValue = defaultValue;
if (scheduler == null) {
scheduler = TaskScheduler.Current;
if (SynchronizationContext.Current != null)
scheduler = TaskScheduler.FromCurrentSynchronizationContext ();
}
this.task.ContinueWith (t => {
IsRunning = false;
}, scheduler);
this.task.ContinueWith (t => {
OnPropertyChanged (nameof(Value));
}, CancellationToken.None, TaskContinuationOptions.OnlyOnRanToCompletion, scheduler);
}
public event PropertyChangedEventHandler PropertyChanged;
public bool IsRunning
{
get { return this.isRunning; }
set
{
if (this.isRunning == value)
return;
this.isRunning = value;
OnPropertyChanged();
}
}
public Task<T> Task => this.task;
public T Value => (this.task.Status == TaskStatus.RanToCompletion) ? this.task.Result : this.defaultValue;
private bool isRunning = true;
private readonly Task<T> task;
private readonly T defaultValue;
private void OnPropertyChanged ([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke (this, new PropertyChangedEventArgs (propertyName));
}
}
}
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