Created
January 16, 2018 07:06
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using System; | |
using System.Reflection; | |
using System.Windows.Input; | |
using Xamarin.Forms; | |
namespace MyNameSpace | |
{ | |
public class EventToCommandBehavior : BehaviorBase<View> | |
{ | |
Delegate eventHandler; | |
public static readonly BindableProperty EventNameProperty = BindableProperty.Create("EventName", typeof(string), typeof(EventToCommandBehavior), null, propertyChanged: OnEventNameChanged); | |
public static readonly BindableProperty CommandProperty = BindableProperty.Create("Command", typeof(ICommand), typeof(EventToCommandBehavior), null); | |
public static readonly BindableProperty CommandParameterProperty = BindableProperty.Create("CommandParameter", typeof(object), typeof(EventToCommandBehavior), null); | |
public static readonly BindableProperty InputConverterProperty = BindableProperty.Create("Converter", typeof(IValueConverter), typeof(EventToCommandBehavior), null); | |
public string EventName | |
{ | |
get { return (string)GetValue(EventNameProperty); } | |
set { SetValue(EventNameProperty, value); } | |
} | |
public ICommand Command | |
{ | |
get { return (ICommand)GetValue(CommandProperty); } | |
set { SetValue(CommandProperty, value); } | |
} | |
public object CommandParameter | |
{ | |
get { return GetValue(CommandParameterProperty); } | |
set { SetValue(CommandParameterProperty, value); } | |
} | |
public IValueConverter Converter | |
{ | |
get { return (IValueConverter)GetValue(InputConverterProperty); } | |
set { SetValue(InputConverterProperty, value); } | |
} | |
protected override void OnAttachedTo(View bindable) | |
{ | |
base.OnAttachedTo(bindable); | |
RegisterEvent(EventName); | |
} | |
protected override void OnDetachingFrom(View bindable) | |
{ | |
base.OnDetachingFrom(bindable); | |
DeregisterEvent(EventName); | |
} | |
void RegisterEvent(string name) | |
{ | |
if (string.IsNullOrWhiteSpace(name)) | |
{ | |
return; | |
} | |
EventInfo eventInfo = AssociatedObject.GetType().GetRuntimeEvent(name); | |
if (eventInfo == null) | |
{ | |
throw new ArgumentException(string.Format("EventToCommandBehavior: Can't register the '{0}' event.", EventName)); | |
} | |
MethodInfo methodInfo = typeof(EventToCommandBehavior).GetTypeInfo().GetDeclaredMethod("OnEvent"); | |
eventHandler = methodInfo.CreateDelegate(eventInfo.EventHandlerType, this); | |
eventInfo.AddEventHandler(AssociatedObject, eventHandler); | |
} | |
void DeregisterEvent(string name) | |
{ | |
if (string.IsNullOrWhiteSpace(name)) | |
{ | |
return; | |
} | |
if (eventHandler == null) | |
{ | |
return; | |
} | |
EventInfo eventInfo = AssociatedObject.GetType().GetRuntimeEvent(name); | |
if (eventInfo == null) | |
{ | |
throw new ArgumentException(string.Format("EventToCommandBehavior: Can't de-register the '{0}' event.", EventName)); | |
} | |
eventInfo.RemoveEventHandler(AssociatedObject, eventHandler); | |
eventHandler = null; | |
} | |
void OnEvent(object sender, object eventArgs) | |
{ | |
if (Command == null) | |
{ | |
return; | |
} | |
object resolvedParameter; | |
if (CommandParameter != null) | |
{ | |
resolvedParameter = CommandParameter; | |
} | |
else if (Converter != null) | |
{ | |
resolvedParameter = Converter.Convert(eventArgs, typeof(object), null, null); | |
} | |
else | |
{ | |
resolvedParameter = eventArgs; | |
} | |
if (Command.CanExecute(resolvedParameter)) | |
{ | |
Command.Execute(resolvedParameter); | |
} | |
} | |
static void OnEventNameChanged(BindableObject bindable, object oldValue, object newValue) | |
{ | |
var behavior = (EventToCommandBehavior)bindable; | |
if (behavior.AssociatedObject == null) | |
{ | |
return; | |
} | |
string oldEventName = (string)oldValue; | |
string newEventName = (string)newValue; | |
behavior.DeregisterEvent(oldEventName); | |
behavior.RegisterEvent(newEventName); | |
} | |
} | |
} |
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