ios–滾動視圖（UIScrollView）詳解

2019-11-14 19:51:16

字體：大中小

來源：轉載

供稿：網友

移動的設備的屏幕大小有限，當一個視圖要顯示的內容大于屏幕尺寸的時候就要用到滾動視圖，比如一個網頁的內容通常比屏幕尺寸大，那么瀏覽器就使用了滾動視圖。

UIScrollView有一個contentSize屬性，聲明如下：

@PRoperty(nonatomic)         CGSize                       contentSize;

這個屬性表示滾動視圖的內容有多大。

創建滾動視圖實例：

- (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];}

效果圖：

contentSize 屬性為{1000,1000}，可以很明顯的看到橫向和縱向滾動條。

1. 滾動

視圖的滾動也沒什么好說的，主要是設置一些屬性：

scrollEnabled 是否開啟滾動

scrollsToTop 默認為YES，用戶可以單擊狀態欄滾動至頂部

bounces 默認為YES，當滾動至邊界時還可以進一步滾動，松開時迅速彈回至原位

directionalLockEnabled 如果為YES,僅可以同時在一個方向上滾動

decelerationRate 在輕彈屏幕后，滾動的速度逐漸衰減，較低的值衰減越快

showsHorizontalScrollIndicator、showsVerticalScrollIndicator 默認為YES，滾動時滾動指示條可見

indicatorStyle 滾動條的樣式（UIScrollViewIndicatorStyleBlack,UIScrollViewIndicatorStyleDefaultUIScrollViewIndicatorStyleWhite）

contentInset 指定內容四周的余量（上左下右的順序）

scrollIndicatorInsets 指定了滾動指示條在位置的切換

contentOffset 內容的定位點，當前顯示內容的左上角

2. 分頁

當內容大于屏幕時就可以分頁，設置pagingEnabled屬性為YES，滾動視圖就不允許用戶自由滑動，只能通過滑動至相鄰的部分。

3. 縮放

使滾動視圖可以縮放需要時設置minimumZoomScale和maximumZoomScale兩個屬性的值（默認為1），還需要在滾動視圖的委托中實現viewForZoomingInScrollView:方法，該方法返回滾動視圖中哪個子視圖是可以縮放的，如果滾動視圖有多個子視圖，但是通常我們需要縮放整個滾動視圖的內容，那么將多個視圖放在一個視圖即可，在將這個視圖成為滾動視圖的子視圖。

滾動視圖通過對捏合手勢的響應進行縮放，如果縮放超出了我們設置的限制，當手勢結束時，尺寸退回到我們設置的限制。如果想要嚴格的限制縮放不超過我們設置的限制，將bouncesZoom設置為NO就可以了。

在某種情況下，比如我們雙擊需要進行縮放的時候，就要用代碼進行縮放，使用下面兩個方法：

- (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：根據比例縮放

zoomToRect：animated：給定矩形的大小進行縮放

4. 委托

UIScrollViewDelegate可以接收大量消息開幫助你跟蹤滾動視圖的工作

下面是協議的定義

@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