两种方法限制拖拽手势的范围

UIGestureRecognizer是一个定义基本手势的抽象类，具体包含：
1、拍击UITapGestureRecognizer (任意次数的拍击)
2、向里或向外捏UIPinchGestureRecognizer (用于缩放)
3、摇动或者拖拽UIPanGestureRecognizer (拖动)
4、擦碰UISwipeGestureRecognizer (以任意方向)
5、旋转UIRotationGestureRecognizer (手指朝相反方向移动)
6、长按UILongPressGestureRecognizer (长按)
本文主要使用到的是拖拽手势：UIPanGestureRecognizer

限制方法：

 -(void)doMoveAction:(UIPanGestureRecognizer *)recognizer{
    // Figure out where the user is trying to drag the view. 
    CGPoint translation = [recognizer translationInView:self.view];
    CGPoint newCenter = CGPointMake(recognizer.view.center.x+ translation.x,
                                    recognizer.view.center.y + translation.y);//    限制屏幕范围：
    newCenter.y = MAX(recognizer.view.frame.size.height/2, newCenter.y);
    newCenter.y = MIN(self.view.frame.size.height - recognizer.view.frame.size.height/2,  newCenter.y);
    newCenter.x = MAX(recognizer.view.frame.size.width/2, newCenter.x);
    newCenter.x = MIN(self.view.frame.size.width - recognizer.view.frame.size.width/2,newCenter.x);
    recognizer.view.center = newCenter;
    [recognizer setTranslation:CGPointZero inView:self.view];
}

也可以使用UITouch来实现：
当手指接触到屏幕，不管是单点触摸还是多点触摸，事件都会开始，直到用户所有的手指都离开屏幕。期间所有的UITouch对象都被包含在UIEvent事件对象中，由程序分发给处理者。事件记录了这个周期中所有触摸对象状态的变化。
限制方法如下：

BOOL isMove;
CGPoint legend_point;
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
   [super touchesBegan:touches withEvent:event];
   isMove = NO;
   UITouch *touch = [touches anyObject];
   CGPoint point = [touch locationInView:self.view];
   if (CGRectContainsPoint(V2.frame, point)) {
       legend_point = [touch locationInView:V2];
       isMove = YES;
   }
}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
   [super touchesMoved:touches withEvent:event];
   if (!isMove) {
       return;
   }
   @autoreleasepool {
       UITouch *touch = [touches anyObject];
       CGPoint point = [touch locationInView:self.view];
       //转化成相对的中心
       point.x += V2.frame.size.width/2.0f - legend_point.x;
       point.y += V2.frame.size.height/2.0f - legend_point.y;
//        限制范围
       if (point.x < V2.frame.size.width / 2.0f) {
           point.x = V2.frame.size.width / 2.0f;
       }
       if (point.y < V2.frame.size.height / 2.0f) {
           point.y = V2.frame.size.height / 2.0f;
       }
       
       if (point.x > self.view.frame.size.width - V2.frame.size.width / 2.0f) {
           point.x = self.view.frame.size.width - V2.frame.size.width / 2.0f;
       }
       if (point.y > self.view.frame.size.height - V2.frame.size.height / 2.0f) {
           point.y = self.view.frame.size.height - V2.frame.size.height / 2.0f;
       }
       V2.center = point;

   }
}

效果如图：

Untitled.gif

Demo下载地址：https://github.com/sinceresk/MoveView