/// <summary>
/// Adds the prefernce specifier observer.
/// </summary>
/// <param name="defaults">Defaults.</param>
/// <param name="action">Action.</param>
public static void AddPrefernceSpecifierObserver(this NSUserDefaults defaults, Action action)
{
defaults.AddObserver("PreferenceSpecifiers", NSKeyValueObservingOptions.New, (observedChange) =>
{
action?.Invoke();
});
}
// createInitialData
//
// The Swift version of this app has a createInitialData method.
// Each child class of the DataManager class overrides this method, and
// then the DataManager base class calls the derived versions to get
// the initial data. C# gives a compiler warning for this ("Virtual
// member call in constructor"). Since in C# the base class constructor
// is run before the child class constructor, having the base clas
// constructor call out to a method on the derived class is calling
// a method on an object that has not yet been fully constructed.
// The C# version of this sample works around this problem by passing
// in the initial data to the constructor.
void ObserveChangesInUserDefaults()
{
var weakThis = new WeakReference <DataManager <ManagedDataType> >(this);
Action <NSObservedChange> changeHandler = (change) =>
{
if (weakThis.TryGetTarget(out var dataManager))
{
// Ignore any change notifications coming from data this
// instance just saved to `NSUserDefaults`.
if (dataManager is null || dataManager.IgnoreLocalUserDefaultsChanges)
{
return;
}
// The underlying data changed in `NSUserDefaults`, so
// update this instance with the change and notify clients
// of the change.
dataManager.LoadData();
dataManager.NotifyClientsDataChanged();
}
};
UserDefaultsObserver = UserDefaults.AddObserver(
StorageDescriptor.Key,
NSKeyValueObservingOptions.Initial | NSKeyValueObservingOptions.New,
changeHandler
);
}
// Notifies clients the data changed by posting an `NSNotification` with
// the key `NotificationKeys.DataChanged`
void NotifyClientsDataChanged()
{
var notification = NSNotification.FromName(NotificationKeys.DataChanged, this);
NSNotificationCenter.DefaultCenter.PostNotification(notification);
}