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Added implementation of base view model and async delegate command
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kirmir committed Oct 15, 2016
1 parent 4ab910a commit ebe541c
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22 changes: 22 additions & 0 deletions WpfAsyncPack.sln
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71 changes: 71 additions & 0 deletions WpfAsyncPack.sln.DotSettings
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135 changes: 135 additions & 0 deletions WpfAsyncPack/AsyncCommand.cs
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using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Input;

namespace WpfAsyncPack
{
public class AsyncCommand<TResult> : AsyncCommandBase, INotifyPropertyChanged
{
private readonly Func<CancellationToken, Task<TResult>> _command;
private readonly CancelAsyncCommand _cancelCommand = new CancelAsyncCommand();

private NotifyTaskCompletion<TResult> _execution;

public event PropertyChangedEventHandler PropertyChanged;

public AsyncCommand(Func<CancellationToken, Task<TResult>> command)
{
_command = command;
}

public ICommand CancelCommand => _cancelCommand;

public NotifyTaskCompletion<TResult> Execution
{
get { return _execution; }
private set
{
_execution = value;
RaisePropertyChanged();
}
}

public override async Task ExecuteAsync(object parameter)
{
_cancelCommand.NotifyCommandStarting();
Execution = new NotifyTaskCompletion<TResult>(_command(_cancelCommand.Token));
RaiseCanExecuteChanged();
await Execution.TaskCompletion;
_cancelCommand.NotifyCommandFinished();
RaiseCanExecuteChanged();
}

public override bool CanExecute(object parameter)
{
return Execution == null || Execution.IsCompleted;
}

protected virtual void RaisePropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}

private sealed class CancelAsyncCommand : ICommand
{
private CancellationTokenSource _cancellationTokenSource = new CancellationTokenSource();
private bool _commandExecuting;

public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}

public CancellationToken Token => _cancellationTokenSource.Token;

void ICommand.Execute(object parameter)
{
_cancellationTokenSource.Cancel();
RaiseCanExecuteChanged();
}

bool ICommand.CanExecute(object parameter)
{
return _commandExecuting && !_cancellationTokenSource.IsCancellationRequested;
}

public void NotifyCommandStarting()
{
_commandExecuting = true;
if (_cancellationTokenSource.IsCancellationRequested)
{
_cancellationTokenSource = new CancellationTokenSource();
RaiseCanExecuteChanged();
}
}

public void NotifyCommandFinished()
{
_commandExecuting = false;
RaiseCanExecuteChanged();
}

private static void RaiseCanExecuteChanged()
{
CommandManager.InvalidateRequerySuggested();
}
}
}

public static class AsyncCommand
{
public static AsyncCommand<object> Create(Func<Task> command)
{
return new AsyncCommand<object>(
async token =>
{
await command();
return null;
});
}

public static AsyncCommand<TResult> Create<TResult>(Func<Task<TResult>> command)
{
return new AsyncCommand<TResult>(token => command());
}

public static AsyncCommand<object> Create(Func<CancellationToken, Task> command)
{
return new AsyncCommand<object>(
async token =>
{
await command(token);
return null;
});
}

public static AsyncCommand<TResult> Create<TResult>(Func<CancellationToken, Task<TResult>> command)
{
return new AsyncCommand<TResult>(command);
}
}
}
29 changes: 29 additions & 0 deletions WpfAsyncPack/AsyncCommandBase.cs
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using System;
using System.Threading.Tasks;
using System.Windows.Input;

namespace WpfAsyncPack
{
public abstract class AsyncCommandBase : IAsyncCommand
{
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}

public async void Execute(object parameter)
{
await ExecuteAsync(parameter);
}

public abstract Task ExecuteAsync(object parameter);

public abstract bool CanExecute(object parameter);

protected void RaiseCanExecuteChanged()
{
CommandManager.InvalidateRequerySuggested();
}
}
}
37 changes: 37 additions & 0 deletions WpfAsyncPack/BaseViewModel.cs
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using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows;
using System.Windows.Threading;

namespace WpfAsyncPack
{
internal abstract class BaseViewModel : INotifyPropertyChanged
{
private readonly Dispatcher _dispatcher = Application.Current.Dispatcher;

public event PropertyChangedEventHandler PropertyChanged;

protected bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string propertyName = null)
{
if (Equals(storage, value))
{
return false;
}

storage = value;

// ReSharper disable once ExplicitCallerInfoArgument
RaisePropertyChangedAsync(propertyName);

return true;
}

protected virtual async void RaisePropertyChangedAsync([CallerMemberName] string propertyName = null)
{
// Run in UI thread.
await _dispatcher.InvokeAsync(
() => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName)),
DispatcherPriority.Normal);
}
}
}
10 changes: 10 additions & 0 deletions WpfAsyncPack/IAsyncCommand.cs
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using System.Threading.Tasks;
using System.Windows.Input;

namespace WpfAsyncPack
{
public interface IAsyncCommand : ICommand
{
Task ExecuteAsync(object parameter);
}
}
84 changes: 84 additions & 0 deletions WpfAsyncPack/NotifyTaskCompletion.cs
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using System;
using System.ComponentModel;
using System.Threading.Tasks;

namespace WpfAsyncPack
{
public sealed class NotifyTaskCompletion<TResult> : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;

public NotifyTaskCompletion(Task<TResult> task)
{
Task = task;

if (!task.IsCompleted)
{
TaskCompletion = WatchTaskAsync(task);
}
}

public Task<TResult> Task { get; }

public Task TaskCompletion { get; }

public TResult Result => Task.Status == TaskStatus.RanToCompletion ? Task.Result : default(TResult);

public TaskStatus Status => Task.Status;

public bool IsCompleted => Task.IsCompleted;

public bool IsNotCompleted => !Task.IsCompleted;

public bool IsSuccessfullyCompleted => Task.Status == TaskStatus.RanToCompletion;

public bool IsCanceled => Task.IsCanceled;

public bool IsFaulted => Task.IsFaulted;

public AggregateException Exception => Task.Exception;

public Exception InnerException => Exception?.InnerException;

public string ErrorMessage => InnerException?.Message;

private async Task WatchTaskAsync(Task task)
{
try
{
await task;
}
catch
{
// Skipped because we handle failures below.
}

var propertyChanged = PropertyChanged;
if (propertyChanged == null)
{
return;
}

propertyChanged(this, new PropertyChangedEventArgs(nameof(Status)));
propertyChanged(this, new PropertyChangedEventArgs(nameof(IsCompleted)));
propertyChanged(this, new PropertyChangedEventArgs(nameof(IsNotCompleted)));

if (task.IsCanceled)
{
propertyChanged(this, new PropertyChangedEventArgs(nameof(IsCanceled)));
}
else if (task.IsFaulted)
{
propertyChanged(this, new PropertyChangedEventArgs(nameof(IsFaulted)));
propertyChanged(this, new PropertyChangedEventArgs(nameof(Exception)));
propertyChanged(this, new PropertyChangedEventArgs(nameof(InnerException)));
propertyChanged(this, new PropertyChangedEventArgs(nameof(ErrorMessage)));
}
else
{
propertyChanged(this, new PropertyChangedEventArgs(nameof(IsSuccessfullyCompleted)));
propertyChanged(this, new PropertyChangedEventArgs(nameof(Result)));
}
}
}
}
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