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iOS里委托與協(xié)議是很重要的一塊,如果理解不好很難區(qū)分協(xié)議與委托到底有什么不一樣,這些東西在開發(fā)中是經(jīng)常遇見的;
協(xié)議是類留給外部的一個接口函數(shù)的集合(一位高手用C++基類來解釋是,把接口做為參數(shù),回調(diào)基類的函數(shù)時,運行時識別,調(diào)用了相應子類的成員函數(shù));
委托是iOS一種設計模式,通過委托別的類,來調(diào)用協(xié)議里的方法,相當于一個回調(diào)過程;
使用理解委托與協(xié)議步驟:
(1) 弄清楚誰委托誰,需要干什么?
拿上一篇博客下拉刷新源碼案例分析,(在源碼工程中comment文件夾里)有MessageSystemView這樣一個類,該類用于用戶的信息所用(比如誰給你留言,或者評論了你某一篇博客),我們也需要刷新獲取最新信息,此處用到下拉刷新第三方類庫EGORefreshTableHeaderView類委托MessageSystemView類來實現(xiàn)這個特性,這就需要在EGORefreshTableHeaderView類定義一個協(xié)議對象delegate。
(2)被委托類需要在interface中聲明<XXDelegate>,表示該類要實現(xiàn)協(xié)議里的方法.
MessageSystemView實現(xiàn)EGORefreshTableHeaderView協(xié)議方法就要遵循EGORefreshTableHeaderDelegate協(xié)議.
(3)在被委托類里定義一個委托類的對象,將xx.delegate=self,意思是把委托的對象只想被委托對象;
在EGORefreshTableHeaderView.h文件中
EGORefreshTableHeaderView*_refreshHeaderView;
在ViewDidLoad中 view.delegate = self; _refreshHeaderView = view;
- (void)viewDidLoad { allCount = 0; [super viewDidLoad]; if (self.tabTitle) { self.tabBarItem.title = self.tabTitle; } //加載固定數(shù)據(jù) imageDownloadsInProgress = [NSMutableDictionary dictionary]; comments = [[NSMutableArray alloc] initWithCapacity:10]; [self reload:YES]; //添加的代碼 if (_refreshHeaderView == nil) { EGORefreshTableHeaderView *view = [[EGORefreshTableHeaderView alloc] initWithFrame:CGRectMake(0.0f, -320.0f, self.view.frame.size.width, 320)]; view.delegate = self; [self.tableComments addSubview:view]; _refreshHeaderView = view; } [_refreshHeaderView refreshLastUpdatedDate]; self.tableComments.backgroundColor = [UIColor colorWithRed:248.0/255.0 green:249.0/255.0 blue:249.0/255.0 alpha:1.0]; }
(4)在被委托類的實現(xiàn)文件中調(diào)用協(xié)議方法,這就是實現(xiàn)委托方法的一個過程;
此處EGORefreshTableHeaderView類對象委托MessageSystemView類對象,在MessageSystemView實現(xiàn)對EGORefreshTableHeaderView類協(xié)議的調(diào)用;
MessageSystemView.m文件實現(xiàn)委托方法
- (void)egoRefreshTableHeaderDidTriggerRefresh:(EGORefreshTableHeaderView *)view { [self reloadTableViewDataSource]; [self refresh]; } - (BOOL)egoRefreshTableHeaderDataSourceIsLoading:(EGORefreshTableHeaderView *)view { return _reloading; } - (NSDate *)egoRefreshTableHeaderDataSourceLastUpdated:(EGORefreshTableHeaderView *)view { return [NSDate date]; }
當然要實現(xiàn)完整的下拉功能這幾個委托只是其中一部分,被委托類里還需要有自己的成員函數(shù),在委托方法正在被調(diào)用的時候觸發(fā)被委托成員函數(shù)方法,在
MessageSystemView.h
//下拉刷新 - (void)refresh;//解析網(wǎng)絡數(shù)據(jù),讓數(shù)據(jù)顯示到視圖上 - (void)reloadTableViewDataSource;//開始加載時調(diào)用此方法 - (void)doneLoadingTableViewData;//完成加載時調(diào)用此方法
#pragma 下提刷新 - (void)reloadTableViewDataSource { _reloading = YES; } - (void)doneLoadingTableViewData { _reloading = NO; [_refreshHeaderView egoRefreshScrollViewDataSourceDidFinishedLoading:self.tableComments]; } - (void)scrollViewDidScroll:(UIScrollView *)scrollView { [_refreshHeaderView egoRefreshScrollViewDidScroll:scrollView]; } - (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate { [_refreshHeaderView egoRefreshScrollViewDidEndDragging:scrollView]; } - (void)egoRefreshTableHeaderDidTriggerRefresh:(EGORefreshTableHeaderView *)view { [self reloadTableViewDataSource]; [self refresh]; } - (BOOL)egoRefreshTableHeaderDataSourceIsLoading:(EGORefreshTableHeaderView *)view { return _reloading; } - (NSDate *)egoRefreshTableHeaderDataSourceLastUpdated:(EGORefreshTableHeaderView *)view { return [NSDate date]; } - (void)refresh { isLoadOver = NO; [self reload:NO]; }
效果圖
.h文件里
#import <UIKit/UIKit.h> #import "EGORefreshTableHeaderView.h" @interface ViewController : UIViewController<UIScrollViewDelegate,UITableViewDelegate,UITableViewDataSource, EGORefreshTableHeaderDelegate> { EGORefreshTableHeaderView *_refreshHeaderView; BOOL _reloading; } @property (retain, nonatomic) IBOutlet UITableView *tableView; -(void)reloadTableViewDataSource; -(void)doneLoadingTableViewData; @end
- (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. if (_refreshHeaderView == nil) { EGORefreshTableHeaderView *view = [[EGORefreshTableHeaderView alloc] initWithFrame:CGRectMake(0.0f, -self.tableView.frame.size.height, self.view.frame.size.width, self.tableView.frame.size.height)]; view.delegate = self; [self.tableView addSubview:view]; _refreshHeaderView = view; [view release]; } [_refreshHeaderView refreshLastUpdatedDate]; } //重新加載時調(diào)用 -(void)reloadTableViewDataSource { _reloading = YES; } //完成加載時調(diào)用 -(void)doneLoadingTableViewData { _reloading = NO; [_refreshHeaderView egoRefreshScrollViewDataSourceDidFinishedLoading:self.tableView]; } #pragma mark - #pragma mark UIScrollViewDelegate Methods -(void)scrollViewDidScroll:(UIScrollView *)scrollView { [_refreshHeaderView egoRefreshScrollViewDidScroll:scrollView]; } -(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate { [_refreshHeaderView egoRefreshScrollViewDidEndDragging:scrollView]; } #pragma mark - #pragma mark EGORefreshTableHeaderDelegate Methods -(void)egoRefreshTableHeaderDidTriggerRefresh:(EGORefreshTableHeaderView *)view { [self reloadTableViewDataSource]; [self performSelector:@selector(doneLoadingTableViewData) withObject:nil afterDelay:3.0]; } -(BOOL)egoRefreshTableHeaderDataSourceIsLoading:(EGORefreshTableHeaderView *)view { return _reloading; } -(NSDate *)egoRefreshTableHeaderDataSourceLastUpdated:(EGORefreshTableHeaderView *)view { return [NSDate date]; } #pragma mark - #pragma mark UITableViewDataSource -(NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return 1; } -(NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return 3; } -(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *cellIdentifier = @"cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier]; if (cell==nil) { cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier]; } cell.textLabel.text = @"下拉刷新測試"; return cell; }
源碼:http://download.csdn.net/detail/duxinfeng2010/4902782
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