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using System;
using Xamarin.Forms.Xaml;
namespace Xamarin.Forms
{
public sealed class BindingCondition : Condition, IValueProvider
{
readonly BindableProperty _boundProperty;
BindingBase _binding;
object _triggerValue;
public BindingCondition()
{
_boundProperty = BindableProperty.CreateAttached("Bound", typeof(object), typeof(BindingCondition), null, propertyChanged: OnBoundPropertyChanged);
}
public BindingBase Binding
{
get { return _binding; }
set
{
if (_binding == value)
return;
if (IsSealed)
throw new InvalidOperationException("Can not change Binding once the Condition has been applied.");
_binding = value;
}
}
public object Value
{
get { return _triggerValue; }
set
{
if (_triggerValue == value)
return;
if (IsSealed)
throw new InvalidOperationException("Can not change Value once the Condition has been applied.");
_triggerValue = value;
}
}
internal IServiceProvider ServiceProvider { get; set; }
internal IValueConverterProvider ValueConverter { get; set; }
object IValueProvider.ProvideValue(IServiceProvider serviceProvider)
{
ValueConverter = serviceProvider.GetService(typeof(IValueConverterProvider)) as IValueConverterProvider;
ServiceProvider = serviceProvider;
return this;
}
internal override bool GetState(BindableObject bindable)
{
object newValue = bindable.GetValue(_boundProperty);
return EqualsToValue(newValue);
}
internal override void SetUp(BindableObject bindable)
{
if (Binding != null)
bindable.SetBinding(_boundProperty, Binding.Clone());
}
internal override void TearDown(BindableObject bindable)
{
bindable.RemoveBinding(_boundProperty);
bindable.ClearValue(_boundProperty);
}
bool EqualsToValue(object other)
{
if ((other == Value) || (other != null && other.Equals(Value)))
return true;
object converted = null;
if (ValueConverter != null)
converted = ValueConverter.Convert(Value, other != null ? other.GetType() : typeof(object), null, ServiceProvider);
else
return false;
return (other == converted) || (other != null && other.Equals(converted));
}
void OnBoundPropertyChanged(BindableObject bindable, object oldValue, object newValue)
{
bool oldState = EqualsToValue(oldValue);
bool newState = EqualsToValue(newValue);
if (newState == oldState)
return;
if (ConditionChanged != null)
ConditionChanged(bindable, oldState, newState);
}
}
}
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