Command

Command

日常开发中必不可少会用到命令，比如button自带了Command和CommandParameter属性。细心的小伙可能会发现并不是所有的控件都自带这样的属性，那么如何让“万物皆可Command”呢？

1. 通常使用System.Windows.Interactivity.dll提供的Interaction对象，它的本质是附加属性可以附加到wpf所有的控件之上，因为所有wpf控件的基类都是DependencyObject的。

2. 避免版本问题，推荐使用Microsoft.Xaml.Behaviors.Wpf 该组件支持5
   

如何使用Interactivity 对象？

1. Install-Package Microsoft.Xaml.Behaviors.Wpf -Version 1.1.31；
2. XAML文件中引入 xmlns:i=；
3. 任意控件标签中添加Interaction.Triggers；
4. 指定EventTrigger的名称，每个控件都会自带一些事件填写该名称即可；
5. 指定InvokeCommandAction最终需要执行的命令；

<StackPanel HorizontalAlignment="Center" VerticalAlignment="Center"><Button Width="120" Height="60"Margin="10" Command="{Binding TestCommand}"Content="click me"></Button><Rectangle Width="120" Height="60"Fill="SeaGreen"></Rectangle><i:Interaction.Triggers><i:EventTrigger EventName="MouseDown"><i:InvokeCommandAction Command="{Binding TestCommand}" /></i:EventTrigger></i:Interaction.Triggers>
</StackPanel>

internal class MainViewModel
{public ICommand TestCommand { get; set; }public MainViewModel() {TestCommand = new RelayCommand(TestCallBack);}private void TestCallBack(){Application.Current.Dispatcher.Invoke(() => {MessageBox.Show("hello world.");});}
}

public class RelayCommand : ICommand
{#region 字段readonly Func<bool> _canExecute;readonly Action _execute;#endregion#region 构造函数public RelayCommand(Action execute) : this(execute, null){}public RelayCommand(Action execute, Func<bool> canExecute){if (execute == null){throw new ArgumentNullException("execute");}_execute = execute;_canExecute = canExecute;}#endregion#region ICommand的成员public event EventHandler CanExecuteChanged{add{if (_canExecute != null)CommandManager.RequerySuggested += value;}remove{if (_canExecute != null)CommandManager.RequerySuggested -= value;}}[DebuggerStepThrough]public Boolean CanExecute(Object parameter){return _canExecute == null ? true : _canExecute();}public void Execute(Object parameter){_execute();}#endregion
}/// <summary>
/// A command whose sole purpose is to 
/// relay its functionality to other
/// objects by invoking delegates. The
/// default return value for the CanExecute
/// method is 'true'.
/// </summary>
public class RelayCommand<T> : ICommand
{#region Constructorspublic RelayCommand(Action<T> execute): this(execute, null){}/// <summary>/// Creates a new command./// </summary>/// <param name="execute">The execution logic.</param>/// <param name="canExecute">The execution status logic.</param>public RelayCommand(Action<T> execute, Predicate<T> canExecute){if (execute == null)throw new ArgumentNullException("execute");_execute = execute;_canExecute = canExecute;}#endregion // Constructors#region ICommand Members[DebuggerStepThrough]public bool CanExecute(object parameter){return _canExecute == null || _canExecute((T)parameter);}public event EventHandler CanExecuteChanged{add{if (_canExecute != null)CommandManager.RequerySuggested += value;}remove{if (_canExecute != null)CommandManager.RequerySuggested -= value;}}public void Execute(object parameter){_execute((T)parameter);}#endregion // ICommand Members#region Fieldsreadonly Action<T> _execute = null;readonly Predicate<T> _canExecute = null;#endregion // Fields
}