c# – 何时何地调用RemoveObserver
发布时间:2020-12-15 20:59:42 所属栏目:百科 来源:网络整理
导读:我有一个UITextView子类,我添加了一个NSNotificationCenter观察器.但是我又在哪里删除了观察者呢? 我的代码: _textDidChangeNotification = UITextView.Notifications.ObserveTextDidChange(TextDidChange); 在Objective C中,我会在dealloc方法中执行此操
我有一个UITextView子类,我添加了一个NSNotificationCenter观察器.但是我又在哪里删除了观察者呢?
我的代码: _textDidChangeNotification = UITextView.Notifications.ObserveTextDidChange(TextDidChange); 在Objective C中,我会在dealloc方法中执行此操作,但我不确定在C#中的相同位置 据我所知,我应该打电话给我 _textDidChangeNotification.Dispose() 我曾尝试过 protected override void Dispose(bool disposing) { base.Dispose(disposing); if (disposing) { _textDidChangeNotification.Dispose(); } } 但它永远不会被称为. 完整的课程,按要求: public class PlaceholderTextView : UITextView { public string Placeholder { get { return PlaceholderLabel.Text; } set { PlaceholderLabel.Text = value; PlaceholderLabel.SizeToFit(); } } protected UILabel PlaceholderLabel { get; set; } protected NSObject _textDidChangeNotification; public override string Text { get { return base.Text; } set { base.Text = value; AdjustPlaceholderHidden(); } } public PlaceholderTextView() { SetupLayout(); _textDidChangeNotification = UITextView.Notifications.ObserveTextDidChange(TextDidChange); } protected override void Dispose(bool disposing) { base.Dispose(disposing); _textDidChangeNotification.Dispose(); } protected void SetupLayout() { PlaceholderLabel = new UILabel(new CGRect(0,9,0)); PlaceholderLabel.TextColor = UIColor.FromWhiteAlpha(0.702f,1f); AddSubview(PlaceholderLabel); } protected void AdjustPlaceholderHidden() { if (Text.Length > 0) { PlaceholderLabel.Hidden = true; } else { PlaceholderLabel.Hidden = false; } } protected void TextDidChange(object sender,Foundation.NSNotificationEventArgs args) { AdjustPlaceholderHidden(); } } 解决方法
我会在ViewWillDisappear中这样做:
public override void ViewWillAppear(bool animated) { base.ViewWillAppear (animated); SubscribeMessages (); } public override void ViewWillDisappear(bool animated) { base.ViewWillDisappear(animated); UnSubscribeMessages (); } public void SubscribeMessages () { _hideObserver = NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillHideNotification,OnKeyboardNotification); _showObserver = NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillShowNotification,OnKeyboardNotification); } public void UnSubscribeMessages () { if (_hideObserver != null) NSNotificationCenter.DefaultCenter.RemoveObserver (_hideObserver); if (_showObserver != null) NSNotificationCenter.DefaultCenter.RemoveObserver(_showObserver); } 或者像Xamarin示例代码here中的ViewDidDis似 更新 同样从这个sample code看起来你正在调用dispose但是它们在ViewDidUnload here上清空了自定义视图: (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |