Prism 3.命令

Prism 3.命令

命令定义

public DelegateCommand SubmitCommand { get; private set; }

    public ArticleViewModel()
    {
        SubmitCommand = new DelegateCommand<object>(Submit, CanSubmit);
    }

    void Submit(object parameter)
    {
        //implement logic
    }

    bool CanSubmit(object parameter)
    {
        return true;
    }

public DelegateCommand SubmitCommand { get; private set; }

    public ArticleViewModel()
    {
        SubmitCommand = new DelegateCommand(Submit, CanSubmit);
    }

    void Submit()
    {
        //implement logic
    }

    bool CanSubmit()
    {
        return true;
    }

警告：使用值类型会造成问题（int, double, bool, etc），可以替换为Nullable

View中嵌入命令：

<Button Command="{Binding SubmitCommand}" CommandParameter="OrderId"/>

当绑定属性变化时，自动更新元素状态

 private bool _isEnabled;
        public bool IsEnabled
        {
            get { return _isEnabled; }
            set
            {
                SetProperty(ref _isEnabled, value);
                SubmitCommand.RaiseCanExecuteChanged();
            }
        }

ObservesProperty：当属性发生变化时，需要在命令中去通知界面属性改变需要使用ObservesProperty，通知命令状态改变，以通知UI状态更改

public class ArticleViewModel : BindableBase
{
    private bool _isEnabled;
    public bool IsEnabled
    {
        get { return _isEnabled; }
        set { SetProperty(ref _isEnabled, value); }
    }

    public DelegateCommand SubmitCommand { get; private set; }

    public ArticleViewModel()
    {
        SubmitCommand = new DelegateCommand(Submit, CanSubmit).ObservesProperty(() => IsEnabled);
    }

    void Submit()
    {
        //implement logic
    }

    bool CanSubmit()
    {
        return IsEnabled;
    }
}

提示：可以注册多重观察属性

ObservesProperty(() => IsEnabled).ObservesProperty(() => CanSave).

ObservesCanExecute：如果CanExcute只是一个简单的bool的话，你可以用ObservesCanExecute去代替委托方法，这也可以去通知UI

private bool _isEnabled;
    public bool IsEnabled
    {
        get { return _isEnabled; }
        set { SetProperty(ref _isEnabled, value); }
    }

    public DelegateCommand SubmitCommand { get; private set; }

    public ArticleViewModel()
    {
        SubmitCommand = new DelegateCommand(Submit, CanSubmit).ObservesCanExecute(() => IsEnabled);
    }

    void Submit()
    {
        //implement logic
    }

警告：无法链式的注册ObservesCanExecute，对于CanExcute委托来说只能观察到一个属性

基于任务的DelegateCommand

基于ICommand是同步的，Excute和CanExcute也是，但是有两种方法去使用异步方法到命令中

1

 public DelegateCommand SubmitCommand { get; private set; }

    public ArticleViewModel()
    {
        SubmitCommand = new DelegateCommand(Submit);
    }

    async void Submit()
    {
        await SomeAsyncMethod();
    }

2

 public DelegateCommand SubmitCommand { get; private set; }

    public ArticleViewModel()
    {
        SubmitCommand = new DelegateCommand(async ()=> await Submit());
    }

    Task Submit()
    {
        return SomeAsyncMethod();
    }