iOS 通過UIPanGestureRecognizer實現控件懸浮拖拽

對控件添加拖拽手勢

UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
[imageView addGestureRecognizer:pan];        //給圖片控件添加手勢

實現拖拽方法：

- (void)handlePan:(UIPanGestureRecognizer *)sender {
    CGFloat screenWidth = [UIScreen mainScreen].bounds.size.width;
    CGFloat screenHeight = [UIScreen mainScreen].bounds.size.height;
    //返回在橫座標上、縱座標上拖動了多少像素
    CGPoint point = [sender translationInView:self.view];
    NSLog(@"%f,%f",point.x,point.y);
    
    CGFloat centerX = sender.view.center.x+point.x;
    CGFloat centerY = sender.view.center.y+point.y;
    CGSize viewSize = sender.view.frame.size;
    
    // top
    if (centerY - viewSize.height/2 < 0) {
        centerY = viewSize.height/2;
    }
    // bottom
    if (centerY + viewSize.height/2 > screenHeight) {
        centerY = screenHeight - viewSize.height/2;
    }
    // left
    if (centerX - viewSize.width/2 < 0){
        centerX = viewSize.width/2;
    }
    // right
    if (centerX + viewSize.width/2 > screenWidth){
        centerX = screenWidth - viewSize.width/2;
    }
    sender.view.center = CGPointMake(centerX, centerY);
    //拖動完之後，每次都要用setTranslation:方法置0這樣才不至於不受控制般滑動出視圖
    [sender setTranslation:CGPointMake(0, 0) inView:self.view];
}

實現控件在屏幕內部拖拽且不脫離屏幕邊界。