// // AsyncValue.cs // // Author: // Eric Maupin // // Copyright (c) 2013-2014 Xamarin, Inc. // // Permission is hereby granted, free of charge, to any person obtaining a copy // of this software and associated documentation files (the "Software"), to deal // in the Software without restriction, including without limitation the rights // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell // copies of the Software, and to permit persons to whom the Software is // furnished to do so, subject to the following conditions: // // The above copyright notice and this permission notice shall be included in // all copies or substantial portions of the Software. // // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN // THE SOFTWARE. using System; using System.ComponentModel; using System.Runtime.CompilerServices; using System.Threading; using System.Threading.Tasks; namespace Xamarin.Forms.Platform.WinPhone { internal sealed class AsyncValue : INotifyPropertyChanged { readonly T _defaultValue; readonly Task _valueTask; bool _isRunning = true; public AsyncValue(Task valueTask, T defaultValue) { if (valueTask == null) throw new ArgumentNullException("valueTask"); _valueTask = valueTask; _defaultValue = defaultValue; TaskScheduler scheduler = TaskScheduler.FromCurrentSynchronizationContext(); _valueTask.ContinueWith(t => { IsRunning = false; }, scheduler); _valueTask.ContinueWith(t => { OnPropertyChanged("Value"); }, CancellationToken.None, TaskContinuationOptions.OnlyOnRanToCompletion, scheduler); } public bool IsRunning { get { return _isRunning; } set { if (_isRunning == value) return; _isRunning = value; OnPropertyChanged(); } } public T Value { get { if (_valueTask.Status != TaskStatus.RanToCompletion) return _defaultValue; return _valueTask.Result; } } public event PropertyChangedEventHandler PropertyChanged; void OnPropertyChanged([CallerMemberName] string propertyName = null) { PropertyChangedEventHandler handler = PropertyChanged; if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName)); } } }