UIScrollView 平滑划动处理

原文链接,请支持原作者:http://blog.csdn.net/gavinming/article/details/6745988

?iOS开发经常会用到UIScrollView，而能够平滑的展示划动效果，是至关重要的。比较常用的方法有两种：

? ? ? 1）将所有的scrollview子页面都add到scrollview中，这样可以平滑滑动，但占用资源加多，并且初始化加载比较慢。

? ? ? 2）使用三个页面View，在滑动过程中如指针轮询那样交替使用。优点是占用内存少，但如果单个页面比较大，经常会在划动到中间位置的时候，出现卡顿，很影响用户体验性。

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? ? ? 第一种方法就不多讲解，如果页面不多，并且每个页面加载的资源也比较少，那么建议采用第一种方式。如果页面比较多，资源比较大，则建议采用延迟加载的方式。

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?更优的方法,请查看：《优化——UIScrollView通过内容延迟加载以达到平滑滑动。》

? ? ? 现在UIScrollView使用有两种方法：一种是App Dev里面的Sample，建立一个包含页面数据的数组，划动的同时，不断添加和删除其他页。而另外一种是定义三个页面，划动过程中，类似与木板搭桥过河游戏一样，prev->current->next->prev，只需重新加载新载入的页面。

1、创建UIScrollView和三个自定义的View：

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[cpp]?view plaincopy

1. ????//***********************************UIScrollView***********************************/??
2. ????scrollView?=?[[UIScrollView?alloc]?initWithFrame:CGRectMake(0,?54,?TOP_BIG_IMAGE_WIDTH,?TOP_BIG_IMAGE_HEIGHT)];??
3. ????scrollView.autoresizingMask?=?UIViewAutoresizingFlexibleWidth;??
4. <span?style="white-space:pre">????</span>self.scrollView.contentSize?=?CGSizeMake(numberOfPages?*?self.scrollView.frame.size.width,???
5. ?????????????????????????????????????????????self.scrollView.frame.size.height);??
6. ????self.scrollView.delegate?=?self;??
7. ????scrollView.autoresizesSubviews?=?YES;??
8. ????scrollView.pagingEnabled?=?YES;??
9. ????scrollView.showsHorizontalScrollIndicator?=?NO;??
10. ????scrollView.scrollsToTop?=?NO;??
11. ????[selfView?addSubview:scrollView];??

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三个自定义View。函数setPageContentWithPageView:(CustomView *)pageView withPageNumber:(NSInteger)pageNumber，是对customview进行更新操作的代码。

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[cpp]?view plaincopy

1. prevPageView?=?[[CustomView?alloc]?initWithFrame:CGRectMake(0,?0,?self.scrollView.frame.size.width,??
2. ????????????????????????????????????????????????????????????self.scrollView.frame.size.height)];??
3. currentPageView?=?[[CustomView?alloc]?initWithFrame:CGRectMake(0,?0,?self.scrollView.frame.size.width,??
4. ???????????????????????????????????????????????????????????????self.scrollView.frame.size.height)];??
5. nextPageView?=?[[CustomView?alloc]?initWithFrame:CGRectMake(0,?0,?self.scrollView.frame.size.width,??
6. ????????????????????????????????????????????????????????????self.scrollView.frame.size.height)];??
7. CGFloat?pageWidth?=?self.scrollView.frame.size.width;??
8. CGFloat?pageHeight?=?self.scrollView.frame.size.height;??
9. ??
10. currentPageView.frame?=?CGRectMake(currentPage?*?pageWidth,?0,?pageWidth,?pageHeight);??
11. [self?setPageContentWithPageView:currentPageView?withPageNumber:currentPage];??
12. ??
13. //第一页??
14. if?(currentPage?==?0)??
15. {??
16. ????prevPageView.frame?=?CGRectZero;??
17. ????nextPageView.frame?=?CGRectMake(((currentPage?+?1)?*?pageWidth),?0,?pageWidth,?pageHeight);??
18. ??????
19. ????if?(numberOfPages?-?1?>=?currentPage?+?1)??
20. ????{??
21. ????????[self?setPageContentWithPageView:nextPageView?withPageNumber:currentPage?+?1];??
22. ????}??
23. }??
24. //最后一页??
25. else?if?(currentPage?==?numberOfPages?-?1)??
26. {??
27. ????prevPageView.frame?=?CGRectMake(((currentPage?-?1)?*?pageWidth),?0,?pageWidth,?pageHeight);??
28. ????nextPageView.frame?=?CGRectZero;??
29. ????[self?setPageContentWithPageView:prevPageView?withPageNumber:currentPage?-?1];??
30. }??
31. else??
32. {??
33. ????prevPageView.frame?=?CGRectMake(((currentPage?-?1)?*?pageWidth),?0,?pageWidth,?pageHeight);???
34. ????nextPageView.frame?=?CGRectMake(((currentPage?+?1)?*?pageWidth),?0,?pageWidth,?pageHeight);??
35. ????[self?setPageContentWithPageView:prevPageView?withPageNumber:currentPage?-?1];??
36. ????[self?setPageContentWithPageView:nextPageView?withPageNumber:currentPage?+?1];??
37. }??
38. ??
39. [self.scrollView?addSubview:currentPageView];??
40. [self.scrollView?addSubview:prevPageView];??
41. [self.scrollView?addSubview:nextPageView];??
42. ??
43. oint?offset?=?CGPointMake(currentPage?*?self.scrollView.frame.size.width,?0);??
44. [self.scrollView?setContentOffset:offset?animated:NO];??

2、在- (void)scrollViewDidScroll:(UIScrollView *)sender方法中进行页面更新。

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?

[cpp]?view plaincopy

1. #pragma?mark?-??
2. #pragma?mark?UIScrollViewDelegate?Methods??
3. ??
4. -?(void)scrollViewDidScroll:(UIScrollView?*)sender??
5. {??
6. ????CGFloat?pageWidth?=?self.scrollView.frame.size.width;??
7. ????NSInteger?page?=?floor((self.scrollView.contentOffset.x?-?pageWidth/2)?/?pageWidth)?+?1;??
8. ??????
9. ????//??已经是第一页再往向前翻页，或者已经是最后一页再往后翻页。??
10. ????if?(currentPage?==?page?||?page?<?0?||?page?>=?numberOfPages)??
11. ????{??????????
12. ????????return;??
13. ????}??
14. ????else??
15. ????{??
16. ????????//先赋值，防止scrollView在执行线程后还未执行currentPage?=?page，导致不断进入该段代码区执行???
17. ????????NSInteger?prevPage?=?currentPage;??
18. ????????currentPage?=?page;??
19. ??????????
20. ????????//防止用户快速滑动，出现因线程未加载完，出现空百夜??
21. ????????self.scrollView.userInteractionEnabled?=?NO;??
22. ????????//线程处理，使得加载动作不会阻塞主线程而出现卡顿。注意，不加afterDelay:0.1，线程会立刻执行，卡顿会出现。??
23. ????????[self?performSelector:@selector(refreshPageViewAfterPaged:)??
24. ???????????????????withObject:[NSNumber?numberWithInteger:prevPage]??
25. ???????????????????afterDelay:0.1];??
26. ????}??
27. }??

函数refreshPageViewAfterPaged是页面的更新操作判断。

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?

[cpp]?view plaincopy

1. -?(void)refreshPageViewAfterPaged:(NSNumber?*)prevPageNumber??
2. {??
3. ????NSAutoreleasePool?*pool??=?[[NSAutoreleasePool?alloc]?init];??
4. ??????
5. ????self.scrollView.userInteractionEnabled?=?YES;??
6. ??????
7. ????CGFloat?pageWidth?=?self.scrollView.frame.size.width;??
8. ????CGFloat?pageHeight?=?self.scrollView.frame.size.height;??
9. ??
10. ????NSInteger?prevPage?=?[prevPageNumber?integerValue];??
11. ????//页面向后滑动一页??
12. ????TopPicView?*tempPageView?=?nil;??
13. ????if?(currentPage?-?1?==?prevPage)??
14. ????{??
15. ????????tempPageView?=?currentPageView;??
16. ????????currentPageView?=?nextPageView;??
17. ????????nextPageView?=?prevPageView;??
18. ????????prevPageView?=?tempPageView;??
19. ??????????
20. ????????prevPageView.frame?=?CGRectMake(((currentPage?-?1)?*?pageWidth),?0,?pageWidth,?pageHeight);??
21. ????????currentPageView.frame?=?CGRectMake(currentPage?*?pageWidth,?0,?pageWidth,?pageHeight);??
22. ??????????
23. ????????if?(currentPage?==?(numberOfPages?-?1))??
24. ????????{??
25. ????????????nextPageView.frame?=?CGRectZero;??
26. ????????}??
27. ????????else??
28. ????????{??
29. ????????????nextPageView.frame?=?CGRectMake(((currentPage?+?1)?*?pageWidth),?0,?pageWidth,?pageHeight);??
30. ????????????//页面更新操作的实质代码：??
31. ????????????[self?setPageContentWithPageView:nextPageView?withPageNumber:currentPage?+?1];??
32. ????????}??
33. ??????????
34. ??????????
35. ????}??
36. ????else?if?(currentPage?+?1?==?prevPage)??
37. ????{??
38. ????????tempPageView?=?currentPageView;??
39. ????????currentPageView?=?prevPageView;??
40. ????????prevPageView?=?nextPageView;??
41. ????????nextPageView?=?tempPageView;??
42. ??????????
43. ????????currentPageView.frame?=?CGRectMake(currentPage?*?pageWidth,?0,?pageWidth,?pageHeight);??
44. ????????nextPageView.frame?=?CGRectMake(((currentPage?+?1)?*?pageWidth),?0,?pageWidth,?pageHeight);??
45. ??????????
46. ????????if?(currentPage?==?0)??
47. ????????{??
48. ????????????prevPageView.frame?=?CGRectZero;??
49. ????????}??
50. ????????else??
51. ????????{??
52. ????????????prevPageView.frame?=?CGRectMake(((currentPage?-?1)?*?pageWidth),?0,?pageWidth,?pageHeight);??
53. ????????????[self?setPageContentWithPageView:prevPageView?withPageNumber:currentPage?-?1];??
54. ????????}??
55. ????}??
56. ??
57. ????[pool?release];??
58. }??