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using System;
using System.ComponentModel;
using System.Reflection;
using Xamarin.Forms.Xaml;
namespace Xamarin.Forms
{
public sealed class PropertyCondition : Condition, IValueProvider
{
readonly BindableProperty _stateProperty;
BindableProperty _property;
object _triggerValue;
public PropertyCondition()
{
_stateProperty = BindableProperty.CreateAttached("State", typeof(bool), typeof(DataTrigger), false, propertyChanged: OnStatePropertyChanged);
}
public BindableProperty Property
{
get { return _property; }
set
{
if (_property == value)
return;
if (IsSealed)
throw new InvalidOperationException("Can not change Property once the Trigger has been applied.");
_property = value;
}
}
public object Value
{
get { return _triggerValue; }
set
{
if (_triggerValue == value)
return;
if (IsSealed)
throw new InvalidOperationException("Can not change Value once the Trigger has been applied.");
_triggerValue = value;
}
}
object IValueProvider.ProvideValue(IServiceProvider serviceProvider)
{
var valueconverter = serviceProvider.GetService(typeof(IValueConverterProvider)) as IValueConverterProvider;
Func<MemberInfo> minforetriever = () => Property.DeclaringType.GetRuntimeProperty(Property.PropertyName);
object value = valueconverter.Convert(Value, Property.ReturnType, minforetriever, serviceProvider);
Value = value;
return this;
}
internal override bool GetState(BindableObject bindable)
{
return (bool)bindable.GetValue(_stateProperty);
}
internal override void SetUp(BindableObject bindable)
{
object newvalue = bindable.GetValue(Property);
bool newState = (newvalue == Value) || (newvalue != null && newvalue.Equals(Value));
bindable.SetValue(_stateProperty, newState);
bindable.PropertyChanged += OnAttachedObjectPropertyChanged;
}
internal override void TearDown(BindableObject bindable)
{
bindable.ClearValue(_stateProperty);
bindable.PropertyChanged -= OnAttachedObjectPropertyChanged;
}
void OnAttachedObjectPropertyChanged(object sender, PropertyChangedEventArgs e)
{
var bindable = (BindableObject)sender;
var oldState = (bool)bindable.GetValue(_stateProperty);
if (Property == null)
return;
if (e.PropertyName != Property.PropertyName)
return;
object newvalue = bindable.GetValue(Property);
bool newstate = (newvalue == Value) || (newvalue != null && newvalue.Equals(Value));
if (oldState != newstate)
bindable.SetValue(_stateProperty, newstate);
}
void OnStatePropertyChanged(BindableObject bindable, object oldValue, object newValue)
{
if ((bool)oldValue == (bool)newValue)
return;
if (ConditionChanged != null)
ConditionChanged(bindable, (bool)oldValue, (bool)newValue);
}
}
}
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