iOS开发之实现文件夹内文件拖出效果

用掌阅iReader看小说时注意到一个文件夹内文件的拖动效果，秉着对未知事物的好奇心态自己试着做了做类似效果^_^，类似下图

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1、原来效果是这样的

2、我实现的效果是这样的

在这里我做了左右边界的限制，图块是不能超出左右屏幕滴！如果拖动结束，图块停留在上下边界我就让图块回到了原位置。

图块拖出灰色视图时灰色视图自动隐藏，不过我们可以将图块拖到底端唤出灰色视图。

3、实现很简单，废话不多说了直接上代码

@interface ViewController ()
{
    CGPoint startPoint;
    UIView *drag;
    UIView *dragBac;
}
@end

#define screenWidth self.view.frame.size.width
#define screenHeight self.view.frame.size.height
- (void)viewDidLoad {
    [super viewDidLoad];
    dragBac=[[UIView alloc]initWithFrame:CGRectMake(0, screenHeight/2, screenWidth, screenHeight/2)];
    dragBac.userInteractionEnabled=YES;
    dragBac.backgroundColor=[UIColor lightGrayColor];
    dragBac.layer.shadowColor = [UIColor blackColor].CGColor;//shadowColor阴影颜色
    dragBac.layer.shadowOffset = CGSizeMake(6,6);//shadowOffset阴影偏移,x向右偏移4，y向下偏移4，默认(0, -3),这个跟shadowRadius配合使用
    dragBac.layer.shadowOpacity = 0.8;//阴影透明度，默认0
    dragBac.layer.shadowRadius = 10;//阴影半径，默认3
    
    [self.view addSubview:dragBac];
    
    drag=[[UIView alloc]initWithFrame:CGRectMake(0, screenHeight/2, 50, 50)];
    drag.backgroundColor=[UIColor blackColor];
    [self.view addSubview:drag];
}

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    //保存触摸起始点位置
    CGPoint point = [[touches anyObject] locationInView:self.view];
    startPoint = point;
}

-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{

    CGPoint point = [[touches anyObject] locationInView:self.view];
    //判断是不是出了左右边界
    point.x=MIN(point.x, screenWidth-25);
    point.x=MAX(point.x, 25);
    
    CGPoint newcenter = CGPointMake(point.x, point.y);
    //移动view
    drag.center = newcenter;
    
    if ((point.y+25)<screenHeight/2) {
        
        [UIView animateWithDuration:0.5 animations:^{
            dragBac.alpha=0;
            
        }];
    }

    //底端唤出视图
    if ((point.y+25)>screenHeight) {
        
        [UIView animateWithDuration:0.5 animations:^{
            dragBac.alpha=1;
            
        }];
    } 
}

- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(nullable UIEvent *)event
{
    CGPoint point = [[touches anyObject] locationInView:self.view];
    
    //未全部拖出，返回原位置
    if (((point.y+25)>screenHeight/2&&(point.y-25)<screenHeight/2)||((point.y+25)>screenHeight&&(point.y-25)<screenHeight)) {
        
        [UIView animateWithDuration:0.5 animations:^{
            drag.frame=CGRectMake(0, screenHeight/2, 50, 50);
            
        }];
    }
}