Change View Content at runtime

I am trying to implement a class for gif-like animation. The class derives from ContentView and I am using a System.Timers.Timer with this method assigned to Elapsed:

public void OnTimedEvent(Object sender, System.Timers.ElapsedEventArgs e){
    ++index;
    Content = new Image () {
        Source = filenames[index],
        Aspect = Aspect.AspectFit
    };
    if (index >= filenames.Count - 1) {
        _timer.Stop ();
    }
}

filenames is List which stores all images I want to show.
But nothing happens on a android device, when the timer elapsed. The displayed content is still the old one. When I rotate the device suddenly all images are shown at the same time.

It seems like the following part from the assembly doesn't work?

public View Content {
    get {
        return this.content;
    }
    set {
        if (this.content == value) {
            return;
        }
        this.OnPropertyChanging ("Content");
        if (this.content != null) {
            base.InternalChildren.Remove (this.content);
        }
        this.content = value;
        if (this.content != null) {
            base.InternalChildren.Add (this.content);
        }
        this.OnPropertyChanged ("Content");
    }
}

How do you change Content at runtime?