/// <summary>
/// Observe collection element's IObservable sequence.
/// </summary>
/// <typeparam name="TCollection">Type of collection</typeparam>
/// <typeparam name="TElement">Type of collection element</typeparam>
/// <typeparam name="TProperty">Type of observable property element</typeparam>
/// <param name="source">Source collection</param>
/// <param name="propertySelector">IObservable selection expression</param>
/// <returns>IObservable sequence</returns>
internal static IObservable <PropertyPack <TElement, TProperty> > ObserveElementObservableProperty <TCollection, TElement, TProperty>(this TCollection source, Expression <Func <TElement, IObservable <TProperty> > > propertySelector)
where TCollection : INotifyCollectionChanged, IEnumerable <TElement>
where TElement : class
{
if (source == null)
{
throw new ArgumentNullException(nameof(source));
}
if (propertySelector == null)
{
throw new ArgumentNullException(nameof(propertySelector));
}
var memberExpression = (MemberExpression)propertySelector.Body;
var propertyInfo = memberExpression.Member as PropertyInfo;
if (propertyInfo == null)
{
throw new ArgumentException($"{nameof(propertySelector)} is not property expression");
}
var propertyName = default(string); // no use
var getter = AccessorCache <TElement> .LookupGet(propertySelector, out propertyName);
return(This.ObserveElementCore <TCollection, TElement, PropertyPack <TElement, TProperty> >
(
source,
(x, observer) => getter(x).Subscribe(y =>
{
var pair = PropertyPack.Create(x, propertyInfo, y);
observer.OnNext(pair);
})
));
}
/// <summary>
/// Converts target property's ErrorsChanged to an observable sequence.
/// </summary>
/// <typeparam name="TSubject">The type of the subject.</typeparam>
/// <typeparam name="TProperty">The type of the property.</typeparam>
/// <param name="subject">The subject.</param>
/// <param name="propertySelector">Argument is self, Return is target property.</param>
/// <returns></returns>
public static IObservable <TProperty> ObserveErrorInfo <TSubject, TProperty>(
this TSubject subject, Expression <Func <TSubject, TProperty> > propertySelector)
where TSubject : INotifyDataErrorInfo
{
var accessor = AccessorCache <TSubject> .LookupGet(propertySelector, out var propertyName);
var result = subject.ErrorsChangedAsObservable()
.Where(e => e.PropertyName == propertyName)
.Select(_ => accessor.Invoke(subject));
return(result);
}
private static IObservable <TProperty> ObserveSimpleProperty <TSubject, TProperty>(
this TSubject subject, Expression <Func <TSubject, TProperty> > propertySelector,
bool isPushCurrentValueAtFirst = true)
where TSubject : INotifyPropertyChanged
{
var isFirst = true;
var accessor = AccessorCache <TSubject> .LookupGet(propertySelector, out var propertyName);
return(Observable.Defer(() =>
{
var flag = isFirst;
isFirst = false;
var q = subject.PropertyChangedAsObservable()
.Where(e => e.PropertyName == propertyName || string.IsNullOrEmpty(e.PropertyName))
.Select(_ => accessor.Invoke(subject));
return (isPushCurrentValueAtFirst && flag) ? q.StartWith(accessor.Invoke(subject)) : q;
}));
}
/// <summary>
/// Converts NotificationObject's property changed to an observable sequence.
/// </summary>
/// <param name="propertySelector">Argument is self, Return is target property.</param>
/// <param name="isPushCurrentValueAtFirst">Push current value on first subscribe.</param>
public static IObservable <TProperty> ObserveProperty <TSubject, TProperty>(
this TSubject subject, Expression <Func <TSubject, TProperty> > propertySelector,
bool isPushCurrentValueAtFirst = true)
where TSubject : INotifyPropertyChanged
{
string propertyName;
var accessor = AccessorCache <TSubject> .LookupGet(propertySelector, out propertyName);
var isFirst = true;
var result = Observable.Defer(() =>
{
var flag = isFirst;
isFirst = false;
var q = subject.PropertyChangedAsObservable()
.Where(e => e.PropertyName == propertyName)
.Select(_ => accessor.Invoke(subject));
return((isPushCurrentValueAtFirst && flag) ? q.StartWith(accessor.Invoke(subject)) : q);
});
return(result);
}