如何创建自定义控件的事件以支持转换为命令?
How to create an event of the Custom control to support converting to the Command?
我创建的自定义控件有一个事件如下。
public class Editor : Control
{
...
public event EventHandler<AlarmCollection> AlarmFired = null;
...
}
当 TextChanged 事件被触发时,上面的事件被调用(如果不为空)。
private async void TextArea_TextChanged(object sender, TextChangedEventArgs e)
{
...
this.AlarmFired?.Invoke(this, this.alarmList);
...
}
现在我尝试将上述事件绑定到外部的 ViewModel,如下所示。
<DataTemplate DataType="{x:Type documentViewModels:EditorTypeViewModel}">
<editor:Editor FontSize="15" FontFamily="Arial"
KeywordForeground="LightBlue">
<i:Interaction.Triggers>
<i:EventTrigger EventName="AlarmFired">
<mvvm:EventToCommand Command="{Binding AlarmFiredCommand}"
PassEventArgsToCommand="True"
EventArgsConverter="{localConverters:RemoveObjectConverter}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</editor:Editor>
</DataTemplate>
EditorTypeViewModel的定义如下图
public class EditorTypeViewModel : DocumentViewModel
{
public event EventHandler<AlarmCollection> AlarmFired = null;
public EditorTypeViewModel(string title) : base(title)
{
}
private RelayCommand<AlarmCollection> alarmFiredCommand = null;
public RelayCommand<AlarmCollection> AlarmFiredCommand
{
get
{
if (this.alarmFiredCommand == null)
this.alarmFiredCommand = new RelayCommand<AlarmCollection>(this.OnAlarmFired);
return this.alarmFiredCommand;
}
}
private void OnAlarmFired(AlarmCollection alarmInfos)
{
this.AlarmFired?.Invoke(this, alarmInfos);
}
}
当我执行上面的程序时,没有调用与RelayCommand 连接的OnAlarmFired 方法。
我试图找出原因,发现了一个可疑点。
疑点是在调用Editor的TextChanged方法时,Editor的AlarmFired事件的值为null。如下所示。
我以为 AlarmFired 不为空,因为它会与 Command 相关联,但事实并非如此。
我尝试做的是将 CustomControl 的事件绑定到 ViewModel 的命令并使用它。
例如,ListView的MouseDoubleClick事件可以绑定到MouseDoubleClickCommand,如下所示。
当触发 MouseDoubleClick 事件时,MouseDoubleClickCommand 将获得控制权。
<ListView>
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseDoubleClick">
<mvvm:EventToCommand Command="{Binding MouseDoubleClickCommand}"
PassEventArgsToCommand="True"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</ListView>
我想创建一个事件来支持转换为像 ListView 的 MouseDoubleClick 这样的命令
(我不想在CustomControl中创建Command,因为事件数量很多)
我应该怎么做才能实现这个目标?
感谢您的阅读。
如果您想将事件参数传递给 ViewModel
,您应该像这样创建一个新的 Behavior
:
public class EventToCommandBehavior : Behavior<FrameworkElement>
{
private Delegate _handler;
private EventInfo _oldEvent;
// Event
public string Event
{
get => (string)GetValue(EventProperty);
set => SetValue(EventProperty, value);
}
public static readonly DependencyProperty EventProperty = DependencyProperty.Register("Event", typeof(string), typeof(EventToCommandBehavior), new PropertyMetadata(null, OnEventChanged));
// Command
public ICommand Command
{
get => (ICommand)GetValue(CommandProperty);
set => SetValue(CommandProperty, value);
}
public static readonly DependencyProperty CommandProperty = DependencyProperty.Register("Command", typeof(ICommand), typeof(EventToCommandBehavior), new PropertyMetadata(null));
// PassArguments (default: false)
public bool PassArguments
{
get => (bool)GetValue(PassArgumentsProperty);
set => SetValue(PassArgumentsProperty, value);
}
public static readonly DependencyProperty PassArgumentsProperty = DependencyProperty.Register("PassArguments", typeof(bool), typeof(EventToCommandBehavior), new PropertyMetadata(false));
private static void OnEventChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var beh = (EventToCommandBehavior)d;
if (beh.AssociatedObject != null) // is not yet attached at initial load
beh.AttachHandler((string)e.NewValue);
}
protected override void OnAttached()
{
AttachHandler(Event); // initial set
}
/// <summary>
/// Attaches the handler to the event
/// </summary>
private void AttachHandler(string eventName)
{
// detach old event
if (_oldEvent != null)
_oldEvent.RemoveEventHandler(AssociatedObject, _handler);
// attach new event
if (!string.IsNullOrEmpty(eventName))
{
var ei = AssociatedObject.GetType().GetEvent(eventName);
if (ei != null)
{
var mi = GetType().GetMethod("ExecuteCommand", BindingFlags.Instance | BindingFlags.NonPublic);
if (mi != null) _handler = Delegate.CreateDelegate(ei.EventHandlerType, this, mi);
ei.AddEventHandler(AssociatedObject, _handler);
_oldEvent = ei; // store to detach in case the Event property changes
}
else
throw new ArgumentException($"The event '{eventName}' was not found on type '{AssociatedObject.GetType().Name}'");
}
}
/// <summary>
/// Executes the Command
/// </summary>
// ReSharper disable once UnusedParameter.Local
private void ExecuteCommand(object sender, EventArgs e)
{
object parameter = PassArguments ? e : null;
if (Command == null) return;
if (Command.CanExecute(parameter))
Command.Execute(parameter);
}
}
并像这样使用:
<ListView>
<i:Interaction.Behaviors>
<behaviors:EventToCommandBehavior Command="{Binding AlarmFiredCommand}" Event="AlarmFired" PassArguments="True" />
</i:Interaction.Behaviors>
</ListView>
注意:如果你想传递你的参数,应该为 PassArguments
属性
设置 True
我创建的自定义控件有一个事件如下。
public class Editor : Control
{
...
public event EventHandler<AlarmCollection> AlarmFired = null;
...
}
当 TextChanged 事件被触发时,上面的事件被调用(如果不为空)。
private async void TextArea_TextChanged(object sender, TextChangedEventArgs e)
{
...
this.AlarmFired?.Invoke(this, this.alarmList);
...
}
现在我尝试将上述事件绑定到外部的 ViewModel,如下所示。
<DataTemplate DataType="{x:Type documentViewModels:EditorTypeViewModel}">
<editor:Editor FontSize="15" FontFamily="Arial"
KeywordForeground="LightBlue">
<i:Interaction.Triggers>
<i:EventTrigger EventName="AlarmFired">
<mvvm:EventToCommand Command="{Binding AlarmFiredCommand}"
PassEventArgsToCommand="True"
EventArgsConverter="{localConverters:RemoveObjectConverter}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</editor:Editor>
</DataTemplate>
EditorTypeViewModel的定义如下图
public class EditorTypeViewModel : DocumentViewModel
{
public event EventHandler<AlarmCollection> AlarmFired = null;
public EditorTypeViewModel(string title) : base(title)
{
}
private RelayCommand<AlarmCollection> alarmFiredCommand = null;
public RelayCommand<AlarmCollection> AlarmFiredCommand
{
get
{
if (this.alarmFiredCommand == null)
this.alarmFiredCommand = new RelayCommand<AlarmCollection>(this.OnAlarmFired);
return this.alarmFiredCommand;
}
}
private void OnAlarmFired(AlarmCollection alarmInfos)
{
this.AlarmFired?.Invoke(this, alarmInfos);
}
}
当我执行上面的程序时,没有调用与RelayCommand 连接的OnAlarmFired 方法。 我试图找出原因,发现了一个可疑点。
疑点是在调用Editor的TextChanged方法时,Editor的AlarmFired事件的值为null。如下所示。
我以为 AlarmFired 不为空,因为它会与 Command 相关联,但事实并非如此。
我尝试做的是将 CustomControl 的事件绑定到 ViewModel 的命令并使用它。
例如,ListView的MouseDoubleClick事件可以绑定到MouseDoubleClickCommand,如下所示。 当触发 MouseDoubleClick 事件时,MouseDoubleClickCommand 将获得控制权。
<ListView>
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseDoubleClick">
<mvvm:EventToCommand Command="{Binding MouseDoubleClickCommand}"
PassEventArgsToCommand="True"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</ListView>
我想创建一个事件来支持转换为像 ListView 的 MouseDoubleClick 这样的命令 (我不想在CustomControl中创建Command,因为事件数量很多)
我应该怎么做才能实现这个目标?
感谢您的阅读。
如果您想将事件参数传递给 ViewModel
,您应该像这样创建一个新的 Behavior
:
public class EventToCommandBehavior : Behavior<FrameworkElement>
{
private Delegate _handler;
private EventInfo _oldEvent;
// Event
public string Event
{
get => (string)GetValue(EventProperty);
set => SetValue(EventProperty, value);
}
public static readonly DependencyProperty EventProperty = DependencyProperty.Register("Event", typeof(string), typeof(EventToCommandBehavior), new PropertyMetadata(null, OnEventChanged));
// Command
public ICommand Command
{
get => (ICommand)GetValue(CommandProperty);
set => SetValue(CommandProperty, value);
}
public static readonly DependencyProperty CommandProperty = DependencyProperty.Register("Command", typeof(ICommand), typeof(EventToCommandBehavior), new PropertyMetadata(null));
// PassArguments (default: false)
public bool PassArguments
{
get => (bool)GetValue(PassArgumentsProperty);
set => SetValue(PassArgumentsProperty, value);
}
public static readonly DependencyProperty PassArgumentsProperty = DependencyProperty.Register("PassArguments", typeof(bool), typeof(EventToCommandBehavior), new PropertyMetadata(false));
private static void OnEventChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var beh = (EventToCommandBehavior)d;
if (beh.AssociatedObject != null) // is not yet attached at initial load
beh.AttachHandler((string)e.NewValue);
}
protected override void OnAttached()
{
AttachHandler(Event); // initial set
}
/// <summary>
/// Attaches the handler to the event
/// </summary>
private void AttachHandler(string eventName)
{
// detach old event
if (_oldEvent != null)
_oldEvent.RemoveEventHandler(AssociatedObject, _handler);
// attach new event
if (!string.IsNullOrEmpty(eventName))
{
var ei = AssociatedObject.GetType().GetEvent(eventName);
if (ei != null)
{
var mi = GetType().GetMethod("ExecuteCommand", BindingFlags.Instance | BindingFlags.NonPublic);
if (mi != null) _handler = Delegate.CreateDelegate(ei.EventHandlerType, this, mi);
ei.AddEventHandler(AssociatedObject, _handler);
_oldEvent = ei; // store to detach in case the Event property changes
}
else
throw new ArgumentException($"The event '{eventName}' was not found on type '{AssociatedObject.GetType().Name}'");
}
}
/// <summary>
/// Executes the Command
/// </summary>
// ReSharper disable once UnusedParameter.Local
private void ExecuteCommand(object sender, EventArgs e)
{
object parameter = PassArguments ? e : null;
if (Command == null) return;
if (Command.CanExecute(parameter))
Command.Execute(parameter);
}
}
并像这样使用:
<ListView>
<i:Interaction.Behaviors>
<behaviors:EventToCommandBehavior Command="{Binding AlarmFiredCommand}" Event="AlarmFired" PassArguments="True" />
</i:Interaction.Behaviors>
</ListView>
注意:如果你想传递你的参数,应该为 PassArguments
属性