為什麼要用Command不用事件
- 改用Command取代掉事件可以避免記憶體洩漏
- 可以降低畫面跟程式的耦合性,可以更好釐清問題發生的地方
- 開發邏輯的人可以直接測試Command引發的動作
定義一個Command
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public class RelayCommand : ICommand
{
private readonly Action<object> _execute;
public event EventHandler CanExecuteChanged;
public bool CanExecute(object parameter)
{
return true;
}
public void Execute(object parameter)
{
_execute.Invoke(parameter);
}
public RelayCommand(Action<object> execute)
{
_execute = execute;
}
}
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引用資源
專案加入參考(我visual studio 2017 community有找到,rider沒有找到)
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| System.Windows.Interactivity.dll
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xaml加入Interactivity NameSpace
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| xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
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元件Binding ViewModel中的Command屬性
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| <Button>
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseEnter">
<i:InvokeCommandAction Command="{Binding ButtonClickCommand}"/>
<i:InvokeCommandAction Command="{Binding ButtonClickCommand}" CommandParameter="{Binding SomeProperty}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</Button>
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| public class ViewModel
{
public RelayCommand ButtonClickCommand { get; set; }
public ViewModel()
{
ButtonClickCommand = new RelayCommand(ButtonClickCommandAction);
}
public void ButtonClickCommandAction(object Parameter)
{
}
}
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4.Command傳遞EventArgs
4.1 安裝MVVMLight
nuget安裝MVVMLight
4.2 xaml引用資源
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| xmlns:cmd="http://www.galasoft.ch/mvvmlight"
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4.3 Binding Command
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| <Button>
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseEnter">
<cmd:EventToCommand PassEventArgsToCommand="true" Command="{Binding OnKeyDown}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</Button>
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4.4 ViewModel
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| using GalaSoft.MvvmLight.CommandWpf;
public RelayCommand<object> OnKeyDown { get; set; }
public void InitCommand()
{
OnKeyDown = new RelayCommand<object>(CommandAction);
}
public void CommandAction(object Parameter)
{
}
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