EventToCommand

EventToCommand

在WPF中，並不是所有控件都有Command，例如TextBox，那么當文本改變，我們需要處理一些邏輯，這些邏輯在ViewModel
中，沒有Command如何綁定呢？這個時候我們就用到EventToCommand，事件轉命令，可以將一些事件例如TextChanged，Checked等
轉換成命令的方式。

不帶參數的EventToCommand

AppView.xaml

       <CheckBox>
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="Checked">
                    <command:EventToCommand Command="{Binding CheckedCommand}"></command:EventToCommand>
                </i:EventTrigger>
                <i:EventTrigger EventName="Unchecked">
                    <command:EventToCommand Command="{Binding UnCheckedCommand}"></command:EventToCommand>
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </CheckBox>

AppViewModel.cs

        public RelayCommand CheckedCommand
        {
            get;
            set;
        }

        public RelayCommand UnCheckedCommand
        {
            get;
            set;
        }

        public AppViewModel()
        {
            CheckedCommand = new RelayCommand(Checked);

            UnCheckedCommand = new RelayCommand(UnChecked);
        }

        private void Checked()
        {
            MessageBox.Show("Checked");
        }

        private void UnChecked()
        {
            MessageBox.Show("Unchecked");
        }

帶參數的EventToCommand

AppView.xaml

        <Button Width="100" Height="30" Margin="0,100,0,0">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="Click">
                    <command:EventToCommand Command="{Binding ShowTxtCommand}" PassEventArgsToCommand="True" CommandParameter="Hello"></command:EventToCommand>
                </i:EventTrigger>
            </i:Interaction.Triggers>
        </Button>

AppViewModel.cs

        /// <summary>
        /// 顯示消息命令
        /// </summary>
        public RelayCommand<string> ShowTxtCommand
        {
            get;
            set;
        }

        public AppViewModel()
        {
            ShowTxtCommand=new RelayCommand<string>(ShowMsg);
        }

        /// <summary>
        /// 命令具體實現
        /// </summary>
        private void ShowMsg(string msg)
        {
            MessageBox.Show(msg);
        }

轉換傳遞的參數

也許你想知道事件是誰觸發的，從而進行一些業務邏輯，那么我們需要從IEventArgsConverter繼承

EventArgsConverter.cs

public class EventArgsConverter : IEventArgsConverter
{
    public object Convert(object value, object parameter)
    {
        var args = (RoutedEventArgs)value;
        var btn = parameter as Button;

        return btn.Name;
    }
}

AppView.xaml

   <Button Width="100" Height="30" Margin="0,100,0,0" x:Name="btn">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="Click">
                <command:EventToCommand Command="{Binding ShowNameCommand}" EventArgsConverter="{StaticResource ArgsConverter}" EventArgsConverterParameter="{Binding ElementName=btn}" PassEventArgsToCommand="True"></command:EventToCommand>
            </i:EventTrigger>
        </i:Interaction.Triggers>
    </Button>

AppViewModel.cs

    public RelayCommand<string> ShowNameCommand
    {
        get;
        set;
    }

    public AppViewModel()
    {

        ShowNameCommand = new RelayCommand<string>(ShowName);
    }

    private void ShowName(string name)
    {
        MessageBox.Show(name);
    }

看了EventToCommand的源碼，並沒有什么幫助，我猜測它的實現是這樣的，EventToCommand屬於附加
屬性，它就能獲取到它所附加的對象即控件本身，然后它還能Binding命令，比如我們附加的對象是Button
，那么就在它的Click事件時，觸發Command命令，同樣，有條件判斷Command是否能執行時，可以設置
控件的IsEnabled屬性。