/// <summary>
/// Strongly bind to PropertyChanged events for a particular property on a particular object
/// </summary>
/// <example>someObject.Bind(x => x.PropertyNameToBindTo, newValue => /* do something with the new value */)</example>
/// <typeparam name="TSource">Type of object providing the PropertyChanged event</typeparam>
/// <typeparam name="TProperty">Type of property for which the event is raised</typeparam>
/// <param name="target">Object raising the PropertyChanged event you're interested in</param>
/// <param name="targetSelector">MemberExpression selecting the property to observe for changes (e.g x => x.PropertyName)</param>
/// <param name="handler">Handler called whenever that property changed</param>
/// <returns>Something which can be used to undo the binding. You can discard it if you want</returns>
///
public static IEventBinding Bind <TSource, TProperty>(this TSource target, Expression <Func <TSource, TProperty> > targetSelector, EventHandler <PropertyChangedExtendedEventArgs <TProperty> > handler) where TSource : class, INotifyPropertyChanged
{
var propertyNamee = targetSelector.ToString();
MemberExpression member = targetSelector.Body as MemberExpression;
PropertyInfo propInfo = member.Member as PropertyInfo;
var propertyName = propInfo.Name;
var propertyAccess = targetSelector.Compile();
// Make sure we don't capture target strongly, otherwise we'll retain it when we shouldn't
// If it does get released, we're released from the delegate list
var weakTarget = new WeakReference <TSource>(target);
PropertyChangedEventHandler ourHandler = (o, e) =>
{
if (e.PropertyName == propertyName || e.PropertyName == String.Empty)
{
TSource strongTarget;
if (weakTarget.TryGetTarget(out strongTarget))
{
handler(strongTarget, new PropertyChangedExtendedEventArgs <TProperty>(propertyName, propertyAccess(strongTarget)));
}
}
};
target.PropertyChanged += ourHandler;
var listener = new StrongPropertyChangedBinding(target, ourHandler);
return(listener);
}
private static IEventBinding BindImpl <TSource, TProperty>(TSource target, Expression <Func <TSource, TProperty> > targetSelector, EventHandler <PropertyChangedExtendedEventArgs <TProperty> > handler, bool invoke) where TSource : class, INotifyPropertyChanged
{
if (target == null)
{
throw new ArgumentNullException(nameof(target));
}
if (targetSelector == null)
{
throw new ArgumentNullException(nameof(targetSelector));
}
if (handler == null)
{
throw new ArgumentNullException(nameof(handler));
}
var propertyName = targetSelector.NameForProperty();
var propertyAccess = targetSelector.Compile();
// Make sure we don't capture target strongly, otherwise we'll retain it when we shouldn't
// If it does get released, we're released from the delegate list
var weakTarget = new WeakReference <TSource>(target);
void ourHandler(object o, PropertyChangedEventArgs e)
{
if (e.PropertyName == propertyName || e.PropertyName == String.Empty)
{
if (weakTarget.TryGetTarget(out TSource strongTarget))
{
handler(strongTarget, new PropertyChangedExtendedEventArgs <TProperty>(propertyName, propertyAccess(strongTarget)));
}
}
}
target.PropertyChanged += ourHandler;
var listener = new StrongPropertyChangedBinding(target, ourHandler);
if (invoke)
{
handler(target, new PropertyChangedExtendedEventArgs <TProperty>(propertyName, propertyAccess(target)));
}
return(listener);
}
