使用UILongPressGestureRecognizer实现拖放UIImageView

Question

我正在实现一个UILongPressGestureRecognizer，它将允许用户在ImageView上长按，然后将图像拖放到其他位置。长按开始后，我缩放视图以指示拖动已准备好，然后用户可以拖动。这是通过每次选择器被更改状态调用时更新ImageViews帧来完成的。这很好，但我想创建视图的副本并将其添加到开始状态的父视图，然后继续在父视图中更新副本的框架。我想这样做，以消除从滚动视图拖动任何问题。虽然我似乎无法在HandleChangeState方法中获得正确的逻辑。该副本只是不正确拖动。

任何想法？

一些代码就在那里，因为我试图为UILabel和UIImageView制作更通用的UILongPressGestureRecognizer，但它不涉及此问题。

public class LearningViewLongPressGestureRecognizer : UILongPressGestureRecognizer 
    { 
     private UIImageView draggedImageView; 
     private UILabel draggedLabel; 
     private RectangleF originalFrame;  
     private UIView parentView; 
     private DRAG_CONTENT_TYPE contentType; 

     public enum DRAG_CONTENT_TYPE 
     { 
      UIIMAGEVIEW, 
      UILabel 
     } 

     public static Selector LongPressSelector 
     { 
      get 
      { 
       return new Selector ("HandleLongPress"); 
      } 
     } 

     public LearningViewLongPressGestureRecognizer (UIView parent, DRAG_CONTENT_TYPE contentType) 
     { 
      this.contentType = contentType; 
      this.AddTarget(this, LongPressSelector); 
      this.Delegate = new LongPressRecognizerDelegate(); 
      this.parentView = parent; 
     } 

     [Export("HandleLongPress")] 
     public void HandleLongPress(UILongPressGestureRecognizer recognizer) 
     { 
      Console.WriteLine ("HandleLongPress Called."); 
      switch (recognizer.State) 
      { 
      case UIGestureRecognizerState.Began: 
       Console.WriteLine ("HandleLongPress Began."); 
       HandleBeginState(recognizer); 
       break; 
      case UIGestureRecognizerState.Changed: 
       Console.WriteLine ("HandleLongPress Changed."); 
       HandleChangedState(recognizer); 
       break; 
      case UIGestureRecognizerState.Cancelled: 
       Console.WriteLine ("HandleLongPress Canceled."); 
       break; 
      case UIGestureRecognizerState.Ended: 
       Console.WriteLine ("HandleLongPress Ended."); 
       break; 
      default: 
       Console.WriteLine ("HandleLongPress Default."); 
       break; 
      } 
     } 

     private void HandleBeginState(UILongPressGestureRecognizer recognizer) 
     { 
      this.originalFrame = this.View.Frame;      

      if (contentType == DRAG_CONTENT_TYPE.UIIMAGEVIEW) 
      { 
       draggedImageView = new UIImageView(); 
       draggedImageView.Image = ((UIImageView)this.View).Image;  
       draggedImageView.Frame = this.View.Frame; 

       //Change the view scale to indicate to the user that the view is selected and ready for dragging. 
       draggedImageView.Transform *= CGAffineTransform.MakeScale(1.1f, 1.1f); 

       parentView.AddSubview(draggedImageView); 
       parentView.BringSubviewToFront(draggedImageView);     
      }        
     } 

     private void HandleChangedState(UILongPressGestureRecognizer recognizer) 
     {   
      PointF currentLocationOfTouchInParentView = recognizer.LocationInView(draggedImageView);//recognizer.TranslationInView(this.View); 
      PointF deltaFromOriginal = new PointF(currentLocationOfTouchInParentView.X - originalFrame.X, currentLocationOfTouchInParentView.Y - originalFrame.Y); 

      RectangleF newFrame = draggedImageView.Frame; 
      newFrame.Offset(deltaFromOriginal.X, deltaFromOriginal.Y); 
      draggedImageView.Frame = newFrame; 
     } 

     private void HandleCanceledState(UILongPressGestureRecognizer recognizer) 
     { 

     } 

     private void HandleEndedState(UILongPressGestureRecognizer recognizer) 
     { 

     } 

     protected class LongPressRecognizerDelegate : UIGestureRecognizerDelegate 
     { 
      public override bool ShouldReceiveTouch (UIGestureRecognizer recognizer, UITouch touch) 
      { 
       return true; 
      } 
     } 
    } 

Answer 1

解决了我的计算问题。我需要采取开始手势的原始触摸位置和父视图内当前触摸位置的增量，然后将该偏移添加到拖动的视图帧。以下是我的解决方案。

private void HandleBeginState(UILongPressGestureRecognizer recognizer) 
     { 
      this.originalFrame = this.View.Frame;      
      this.originalTouchLocation = recognizer.LocationInView(parentView); 

      if (contentType == DRAG_CONTENT_TYPE.UIIMAGEVIEW) 
      { 
       draggedImageView = new UIImageView(); 
       draggedImageView.Image = ((UIImageView)this.View).Image;  
       draggedImageView.Frame = new RectangleF(originalFrame.X, originalFrame.Y, originalFrame.Size.Width, originalFrame.Size.Height); 

       parentView.AddSubview(draggedImageView); 
       parentView.BringSubviewToFront(draggedImageView); 

       //Change the view scale to indicate to the user that the view is selected and ready for dragging. 
       draggedImageView.Transform *= CGAffineTransform.MakeScale(1.1f, 1.1f); 
      }        
     } 

     private void HandleChangedState(UILongPressGestureRecognizer recognizer) 
     {   
      PointF currentLocationOfTouchInParentView = recognizer.LocationInView(parentView); 
      PointF deltaFromOriginalTouch = new PointF(currentLocationOfTouchInParentView.X - originalTouchLocation.X, currentLocationOfTouchInParentView.Y - originalTouchLocation.Y); 

      RectangleF newFrame = originalFrame; 
      newFrame.Offset(deltaFromOriginalTouch.X, deltaFromOriginalTouch.Y); 
      draggedImageView.Frame = newFrame;   
     }