/// <summary>
/// 设定在指定属性发生更改时，通知当前命令的可执行状态已更改。
/// </summary>
/// <param name="source">发出属性更改通知的事件源对象。</param>
/// <param name="propertyName">要接收更改通知的属性的名称。</param>
/// <returns>当前 <see cref="DelegateCommand"/> 实例。</returns>
/// <exception cref="ArgumentNullException">
/// <paramref name="source"/> 为 <see langword="null"/>。</exception>
public DelegateCommand ObserveCanExecute(
INotifyPropertyChanged source, string propertyName)
{
if (source is null)
{
throw new ArgumentNullException(nameof(source));
}
var observer = new CanExecuteObserver(this, propertyName);
source.PropertyChanged += observer.OnPropertyChanged;
return(this);
}
public AsyncCommandBuilder ObservesCanExecute([NotNull] Expression <Func <bool> > canExecute, bool fallback)
{
if (canExecute == null)
{
throw new ArgumentNullException(nameof(canExecute));
}
if (this.canExecuteSubject != null)
{
throw new CommandBuilderException(ExceptionStrings.CanExecuteExpressionAlreadyDefined);
}
if (this.canExecuteFunction != null)
{
throw new CommandBuilderException(ExceptionStrings.CanExecuteFunctionAlreadyDefined);
}
this.canExecuteSubject = CanExecuteObserver.Create(canExecute, fallback);
return(this);
}
