Storyboard学习六(ScrollView)

ScrollView
UIScrollView就是可以滚动的视图，常常用在图片显示（缩放，滚动等），文本显示等，是一个非常有用的控件。

    //声明一个scrollView
    scrollView = [[UIScrollView alloc]initWithFrame:CGRectMake(0, 50, widthOut, self.view.frame.size.height-50)];
    scrollView.backgroundColor = [UIColor redColor];

    //任意滑动
    scrollView.pagingEnabled = NO;

    //滑动过程中显示水平滚动条（如果有）
    scrollView.showsHorizontalScrollIndicator = YES;

    //滑动过程中显示垂直滚动条（如果有）
    scrollView.showsVerticalScrollIndicator = YES;

    //点击顶部的状态栏滚动到首
    scrollView.scrollsToTop = YES;
    scrollView.delegate = self;

    [self.view addSubview:scrollView];

要使用 UIScrollView，则必须实现 UIScrollViewDelegate，该Delegate定义如下：

@protocol UIScrollViewDelegate<NSObject>  

@optional  

- (void)scrollViewDidScroll:(UIScrollView *)scrollView;                                               // any offset changes  
- (void)scrollViewDidZoom:(UIScrollView *)scrollView __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_3_2); // any zoom scale changes  

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView;                              // called on start of dragging (may require some time and or distance to move)  
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate; // called on finger up if user dragged. decelerate is true if it will continue moving afterwards  

- (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 __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_3_2); // called before the scroll view begins zooming its content  
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)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  

有几个是比较重要的：
scrollViewDidScroll：scrollView只要在滚动就会触发该方法（无论是被用户拖动还是在拖动后scrollView由于惯性继续滚动一点距离）
scrollViewWillBeginDragging：scrollView被用户拖动前就会触发该方法

scrollViewDidEndDragging：scrollView被用户拖动结束后就会触发该方法

scrollViewWillBeginDecelerating：scrollView在拖动后继续滚动前就会触发该方法

scrollViewDidEndDecelerating：scrollView在拖动后继续滚动后停止就会触发该方法

scrollViewShouldScrollToTop：返回YES或NO，表示是否支持用户点击屏幕顶端的状态条后scrollView滚动到顶端（默认YES）

scrollViewDidScrollToTop：用户点击屏幕顶端的状态条后scrollView滚动到顶端后会触发该方法（scrollViewShouldScrollToTop如果返回NO，则该方法不会被触发）

UIScrollView的常用属性如下：

scrollView.pagingEnabled = NO;  

//划动过程中显示水平滚动条(如果有)  
scrollView.showsHorizontalScrollIndicator = YES;  

//划动过程中显示垂直滚动条(如果有)  
scrollView.showsVerticalScrollIndicator = YES;  

//点击顶部的状态栏滚动到首  
scrollView.scrollsToTop = YES;  
scrollView.delegate = self;  
scrollView.contentSize = CGRect  

pagingEnabled：是否以整数倍的UIScrollView大小滚动（如果是用于图片类的UIScrollView，该值应该设置为YES，如果是用于显示文本类的UIScrollView或者类似与本例的允许用户滚动到任意位置的情况时应该设置为NO）
contentOffset：UIScrollView中content的左上角坐标
contentSize：UIScrollView中content的大小，该值与UIScrollView的大小决定滚动条的长短
decelerating：UIScrollView在拖动放手后是否仍在由于惯性继续滚动中
dragging：UIScrollView是否正在被用户拖动
showsHorizontalScrollIndicator：是否显示水平滚动条
showsVerticalScrollIndicator：是否显示垂直滚动条