C# 当使用CommandManager.InvalidateRequestSuggested（）时？

有时UI未更新，因此需要使用命令刷新命令。（RelayCommand）。例如，启用或禁用按钮。 我在那里寻找如何解决这个问题，我找到了这个解决方案CommandManager.invalidateRequestSuggested（）。 这是可行的，但我发现，“CommandManager.invalidateRequestSuggested（）尝试验证所有命令，这是完全无效的（在您的情况下是缓慢的）-在每次更改中，您都要求每个命令重新检查其CanExecute（）” 我做过一些应用程序（代码隐藏与我遇到的问题非常相似），我遇到了这个问题。 当方法执行结束时，按钮没有更新，我需要在UI上单击一次

...
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.CommandWpf;
...
...
private ICommand _downloadCommand;
        public ICommand DownloadCommand
        {
            get
            {
                return _downloadCommand ?? (_downloadCommand = new RelayCommand(Download, () => IsEnabled));
            }
        }

        private ICommand _cancelDownloadCommand;
        public ICommand CancelDownloadCommand
        {
            get
            {
                return _cancelDownloadCommand ?? (_cancelDownloadCommand = new RelayCommand(CancelDownload, () => IsEnabledCancel));
            }
        }

        private bool _isEnabled = true;
        private bool IsEnabled
        {
            get { return _isEnabled; }
            set
            {
                _isEnabled = value;
                RaisePropertyChanged();
            }
        }

        private bool _isEnabledCancel;
        private bool IsEnabledCancel
        {
            get { return _isEnabledCancel; }
            set
            {
                _isEnabledCancel = value;
                RaisePropertyChanged();
            }
        }

private async void Download()
        {

            IsEnabled = false;

            IsEnabledCancel = true;

            await Task.Run(() =>
            {

                ...
                ...
                ...
                ...
                ...

            });

            IsEnabled = true;

            IsEnabledCancel = false;

        }

.XAML

     <DockPanel Dock="Top">
        <Button Margin="5" VerticalAlignment="Top" HorizontalAlignment="Center" Command="{Binding CancelDownloadCommand}" FontSize="20" 
                Background="Transparent" BorderThickness="2" BorderBrush="{StaticResource AccentColorBrush4}" ToolTip="Cancel"
                DockPanel.Dock="Right">
            <StackPanel Orientation="Horizontal">
                <Image Source="Images/48x48/Error.png" Height="48" Width="48"/>
                <Label Content="{Binding ToolTip, RelativeSource={RelativeSource AncestorType={x:Type Button}}}" FontFamily="Segoe UI Light"/>
            </StackPanel>
        </Button>
        <Button Margin="5" VerticalAlignment="Top" HorizontalAlignment="Center" Command="{Binding DownloadCommand}" FontSize="20" 
                Background="Transparent" BorderThickness="2" BorderBrush="{StaticResource AccentColorBrush4}" ToolTip="Download"
                DockPanel.Dock="Right">
            <StackPanel Orientation="Horizontal">
                <Image Source="Images/48x48/Download.png" Height="48" Width="48"/>
                <Label Content="{Binding ToolTip, RelativeSource={RelativeSource AncestorType={x:Type Button}}}" FontFamily="Segoe UI Light"/>
            </StackPanel>
        </Button>
    </DockPanel>