c# - 从子控件检测 ViewDidUnload

Question

我试图弄清楚如何挂接到控件的 super View 上的ViewDidUnload。为了说明我为什么需要这个，请考虑我的 ControlFactory 类，它生成 UIButton(以及其他控件):

internal static class ControlFactory
{
        private static readonly IObservable<Unit> sharedDynamicTypeChanged = TinyIoCContainer.Current
            .Resolve<ISystemNotificationsService>()
            .DynamicTypeChanged
            .Publish()
            .RefCount();

        public static UIButton CreateButton()
        {
            return new DynamicTypeAwareButton(sharedDynamicTypeChanged, UIFont.PreferredHeadline);
        }
}

这里的想法是，工厂生产的每个 UIButton 都会根据用户的动态类型设置自动缩放其字体。我的 DynamicTypeAwareButton 是一个内部类，如下所示:

private sealed class DynamicTypeAwareButton : UIButton
{
    private readonly IObservable<Unit> dynamicTypeChanged;
    private readonly UIFont font;
    private IDisposable subscription;

    public DynamicTypeAwareButton(IObservable<Unit> dynamicTypeChanged, UIFont font)
    {
        this.dynamicTypeChanged = dynamicTypeChanged;
        this.font = font;
    }

    public override void MovedToSuperview()
    {
        base.MovedToSuperview();

        // TODO: figure out when to subscribe/unsubscribe
        this.subscription = this.dynamicTypeChanged
            .StartWith(Unit.Default)
            .Subscribe(_ => this.UpdateFont());
    }

    private void UpdateFont()
    {
        this.Font = this.font;
    }
}

如评论中所述，问题是我需要知道按钮的 super View 何时卸载，以便我可以处理订阅。我可以轻松访问 super View ，但我找不到任何在卸载该 super View 时收到通知的 Hook 。

有谁知道有什么方法可以实现这一目标吗？

Answer 1

而不是 MovedToSuperView 使用 WillMoveToSuperView - 它会被调用两次，一次是在按钮被添加到 View 时(即 => 订阅)，一次是在按钮被添加到 View 时即将被丢弃(其中 newSuperview 将为空)。

此外，您可以使用 SerialDisposable 更优雅地编写它:

private sealed class DynamicTypeAwareButton : UIButton
{
    private readonly IObservable<Unit> dynamicTypeChanged;
    private readonly UIFont font;
    private SerialDisposable subscription = new SerialDisposable();

    public override void WillMoveToSuperView(UIView newView)
    {
        base.WillMoveToSuperView();

        // Whenever SerialDisposable.Disposable is assigned, it throws
        // away the previous one. That means, even if the Button gets
        // moved to a new non-null View, we're still not leaking a 
        // subscription
        if (newView != null) 
        {
            this.subscription.Disposable = this.dynamicTypeChanged
                .StartWith(Unit.Default)
                .Subscribe(_ => this.UpdateFont());
        } 
        else 
        {
            this.subscription.Disposable = Disposable.Empty;
        }
    }

    public void UpdateFont()
    {
        /* ... */
    }
}