/// <summary>
/// Cancel a subscription that was created by calling <see cref="Subscribe{T}(IQueryable{T}, SubscriptionOptions, Expression{Func{T, IQueryable}}[])"/>.
/// <para />
/// Removing a subscription will delete all objects from the local Realm that were matched
/// only by that subscription and not any remaining subscriptions. The deletion is performed
/// by the server, and so has no immediate impact on the contents of the local Realm. If the
/// device is currently offline, the removal will not be processed until the device returns online.
/// </summary>
/// <typeparam name="T">The type of the objects that make up the subscription query.</typeparam>
/// <param name="subscription">The subscription to cancel.</param>
/// <returns>An awaitable task, that indicates that the subscription has been removed locally.</returns>
public static async Task UnsubscribeAsync <T>(this Subscription <T> subscription)
{
Argument.NotNull(subscription, nameof(subscription));
if (subscription.State == SubscriptionState.Invalidated)
{
return;
}
AsyncHelper.EnsureValidContext();
subscription.Handle.Unsubscribe();
var tcs = new TaskCompletionSource <object>();
PropertyChangedEventHandler handler = null;
handler = new PropertyChangedEventHandler((s, e) =>
{
switch (subscription.State)
{
case SubscriptionState.Invalidated:
tcs.TrySetResult(null);
break;
case SubscriptionState.Error:
tcs.TrySetException(subscription.Error);
break;
}
});
subscription.PropertyChanged += handler;
try
{
await tcs.Task;
}
finally
{
subscription.PropertyChanged -= handler;
subscription.SubscriptionToken.Dispose();
}
}
