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using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
namespace Xamarin.Forms
{
[ContentProperty("Actions")]
public sealed class EventTrigger : TriggerBase
{
static readonly MethodInfo s_handlerinfo = typeof(EventTrigger).GetRuntimeMethods().Single(mi => mi.Name == "OnEventTriggered" && mi.IsPublic == false);
readonly List<BindableObject> _associatedObjects = new List<BindableObject>();
EventInfo _eventinfo;
string _eventname;
Delegate _handlerdelegate;
public EventTrigger() : base(typeof(BindableObject))
{
Actions = new SealedList<TriggerAction>();
}
public IList<TriggerAction> Actions { get; }
public string Event
{
get { return _eventname; }
set
{
if (_eventname == value)
return;
if (IsSealed)
throw new InvalidOperationException("Event cannot be changed once the Trigger has been applied");
OnPropertyChanging();
_eventname = value;
OnPropertyChanged();
}
}
internal override void OnAttachedTo(BindableObject bindable)
{
base.OnAttachedTo(bindable);
if (!string.IsNullOrEmpty(Event))
AttachHandlerTo(bindable);
_associatedObjects.Add(bindable);
}
internal override void OnDetachingFrom(BindableObject bindable)
{
_associatedObjects.Remove(bindable);
DetachHandlerFrom(bindable);
base.OnDetachingFrom(bindable);
}
internal override void OnSeal()
{
base.OnSeal();
((SealedList<TriggerAction>)Actions).IsReadOnly = true;
}
void AttachHandlerTo(BindableObject bindable)
{
try
{
_eventinfo = bindable.GetType().GetRuntimeEvent(Event);
_handlerdelegate = s_handlerinfo.CreateDelegate(_eventinfo.EventHandlerType, this);
}
catch (Exception)
{
Log.Warning("EventTrigger", "Can not attach EventTrigger to {0}.{1}. Check if the handler exists and if the signature is right.", bindable.GetType(), Event);
}
if (_eventinfo != null && _handlerdelegate != null)
_eventinfo.AddEventHandler(bindable, _handlerdelegate);
}
void DetachHandlerFrom(BindableObject bindable)
{
if (_eventinfo != null && _handlerdelegate != null)
_eventinfo.RemoveEventHandler(bindable, _handlerdelegate);
}
[Preserve]
void OnEventTriggered(object sender, EventArgs e)
{
var bindable = (BindableObject)sender;
foreach (TriggerAction action in Actions)
action.DoInvoke(bindable);
}
}
}
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