ios – 滚动视图（UIScrollView）详解

浏览数：24 / 时间：2015年06月11日

移动的设备的屏幕大小有限，当一个视图要显示的内容大于屏幕尺寸的时候就要用到滚动视图，比如一个网页的内容通常比屏幕尺寸大，那么浏览器就使用了滚动视图。

UIScrollView有一个contentSize属性，声明如下：

@property(nonatomic)         CGSize                       contentSize;

这个属性表示滚动视图的内容有多大。

创建滚动视图实例：

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    UIScrollView *sv = [[UIScrollView alloc] initWithFrame:self.view.frame];
    sv.contentSize = CGSizeMake(1000, 1000);
    sv.backgroundColor = [UIColor redColor];
    [self.view addSubview:sv];
}

效果图：

contentSize 属性为{1000,1000}，可以很明显的看到横向和纵向滚动条。

1. 滚动

视图的滚动也没什么好说的，主要是设置一些属性：

scrollEnabled 是否开启滚动

scrollsToTop 默认为YES，用户可以单击状态栏滚动至顶部

bounces 默认为YES，当滚动至边界时还可以进一步滚动，松开时迅速弹回至原位

directionalLockEnabled 如果为YES,仅可以同时在一个方向上滚动

decelerationRate 在轻弹屏幕后，滚动的速度逐渐衰减，较低的值衰减越快

showsHorizontalScrollIndicator、showsVerticalScrollIndicator 默认为YES，滚动时滚动指示条可见

indicatorStyle 滚动条的样式（UIScrollViewIndicatorStyleBlack,UIScrollViewIndicatorStyleDefaultUIScrollViewIndicatorStyleWhite）

contentInset 指定内容四周的余量（上左下右的顺序）

scrollIndicatorInsets 指定了滚动指示条在位置的切换

contentOffset 内容的定位点，当前显示内容的左上角

2. 分页

当内容大于屏幕时就可以分页，设置pagingEnabled属性为YES，滚动视图就不允许用户自由滑动，只能通过滑动至相邻的部分。

3. 缩放

使滚动视图可以缩放需要时设置minimumZoomScale和maximumZoomScale两个属性的值（默认为1），还需要在滚动视图的委托中实现viewForZoomingInScrollView:方法，该方法返回滚动视图中哪个子视图是可以缩放的，如果滚动视图有多个子视图，但是通常我们需要缩放整个滚动视图的内容，那么将多个视图放在一个视图即可，在将这个视图成为滚动视图的子视图。

滚动视图通过对捏合手势的响应进行缩放，如果缩放超出了我们设置的限制，当手势结束时，尺寸退回到我们设置的限制。如果想要严格的限制缩放不超过我们设置的限制，将bouncesZoom设置为NO就可以了。

在某种情况下，比如我们双击需要进行缩放的时候，就要用代码进行缩放，使用下面两个方法：

- (void)setZoomScale:(CGFloat)scale animated:(BOOL)animated NS_AVAILABLE_IOS(3_0);
- (void)zoomToRect:(CGRect)rect animated:(BOOL)animated NS_AVAILABLE_IOS(3_0);

setZoomScale：animated：根据比例缩放

zoomToRect：animated：给定矩形的大小进行缩放

4. 委托

UIScrollViewDelegate可以接收大量消息开帮助你跟踪滚动视图的工作

下面是协议的定义

@protocol UIScrollViewDelegate<NSObject>

@optional

- (void)scrollViewDidScroll:(UIScrollView *)scrollView;                                               // any offset changes
- (void)scrollViewDidZoom:(UIScrollView *)scrollView NS_AVAILABLE_IOS(3_2); // any zoom scale changes

// called on start of dragging (may require some time and or distance to move)
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView;
// called on finger up if the user dragged. velocity is in points/millisecond. targetContentOffset may be changed to adjust where the scroll view comes to rest
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset NS_AVAILABLE_IOS(5_0);
// called on finger up if the user dragged. decelerate is true if it will continue moving afterwards
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate;

- (void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView;   // called on finger up as we are moving
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView;      // called when scroll view grinds to a halt

- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView; // called when setContentOffset/scrollRectVisible:animated: finishes. not called if not animating

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView;     // return a view that will be scaled. if delegate returns nil, nothing happens
- (void)scrollViewWillBeginZooming:(UIScrollView *)scrollView withView:(UIView *)view NS_AVAILABLE_IOS(3_2); // called before the scroll view begins zooming its content
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(CGFloat)scale; // scale between minimum and maximum. called after any ‘bounce‘ animations

- (BOOL)scrollViewShouldScrollToTop:(UIScrollView *)scrollView;   // return a yes if you want to scroll to the top. if not defined, assumes YES
- (void)scrollViewDidScrollToTop:(UIScrollView *)scrollView;      // called when scrolling animation finished. may be called immediately if already at top

@end