iOS学习笔记13— UITableView封装之下拉-上提-图片异步加载

做过移动端开发的人都知道，列表控件是最常用的控件之一。iOS里的列表控件是UITableView，其实Apple的开发人员对于UITableView的设计已经够好的了(简单易用，扩展性非常强等等)。

但对于展示逻辑单一的移动端系统软件，你还是能感觉到有些繁琐(或许是程序员天生就有些懒惰的毛病吧)。

来看看它到底繁琐在哪儿了。首先，它的使用频率太高了；第二，它通常不是只呈现一下数据就完事了，一般都会跟随下拉刷新、上提加载更多功能，当然通常还要跟网络下载数据、图片打交道；第三，MVC模式是ios开发的惯用模式，随之而来的是一大堆协议的实现(无论你是再写一次也好，拷贝也罢，反正做这些工作都让人觉得索然无味)。

冲着这些，今天就把UITableView常见的使用模式封装了一下。具体做了以下几件事：

1、  内嵌了下拉刷新(EGORefreshTableHeaderView)、上提加载更多(LoadMoreTableFooterView)

2、  内置实现了UITableViewDataSource、UITableViewDelegate这两个通常必须实现的协议，对于自实现的逻辑以Block的形式对客户代码开放

3、  内置实现了1中提到的两个组件的回调协议，同上，自实现的逻辑以Block的形式对外开放

4、  内置实现了EGORefreshTableHeaderView、LoadMoreTableFooterView与UITableView交互必须实现的UIScrollViewDelegate协议

5、  内置实现了异步图片下载(可选)

 

你可以到我的Github上，查看源码。称它为ELTableViewController是取了EGORefreshTableHeaderView以及LoadMoreTableFooterView的首字母。

这份代码中包含了一个示例程序以及三个必备组件：

1、  EGORefreshTableHeaderView

2、  LoadMoreTableFooterView(修改版，原版不能适应任何尺寸的高度)

3、  Apple官方提供的异步下载UITableView中的图片的示例组件(IconDownLoader)，这个只适用于下载类似于社交网络中的用户头像，不建议使用它来下载那些大图片，因为它甚至都没有缓存(如果图片很大，推荐使用SDImage)

代码解读

它已经内置实现了这些协议，所以在你使用它的时候，无需设置和实现。

 @interface ELTableViewController : UIViewController
 <
 UITableViewDelegate,
 UITableViewDataSource,
 EGORefreshTableHeaderDelegate,
 LoadMoreTableFooterDelegate,
 IconDownloaderDelegate
 >

对于不断变化的业务逻辑，这里提供了所有需要实现的block：

 //blocks for UITableView delegate
 typedef UITableViewCell* (^cellForRowAtIndexPathDelegate) (UITableView *,NSIndexPath *);
 typedef CGFloat (^heightForRowAtIndexPathDelegate) (UITableView *,NSIndexPath *);
 typedef void (^didSelectRowAtIndexPathDelegate) (UITableView *,NSIndexPath *);

 //blocks for refresh and load more
 typedef void (^refreshDataSourceFunc) (void);
 typedef void (^loadMoreDataSourceFunc) (void);

 typedef void (^refreshDataSourceCompleted) (void);
 typedef void (^loadMoreDataSourceCompleted) (void);
 //use to load image (async)
 typedef void (^loadImagesForVisiableRowsFunc) (void);
 typedef void (^appImageDownloadCompleted) (NSIndexPath *);

它们以属性的形式对外公开：

 //property for blocks
 @property (nonatomic,copy) cellForRowAtIndexPathDelegate cellForRowAtIndexPathDelegate;
 @property (nonatomic,copy) heightForRowAtIndexPathDelegate heightForRowAtIndexPathDelegate;
 @property (nonatomic,copy) didSelectRowAtIndexPathDelegate didSelectRowAtIndexPathDelegate;

 @property (nonatomic,copy) loadMoreDataSourceFunc loadMoreDataSourceFunc;
 @property (nonatomic,copy) refreshDataSourceFunc refreshDataSourceFunc;
 @property (nonatomic,copy) refreshDataSourceCompleted refreshDataSourceCompleted;
 @property (nonatomic,copy) loadMoreDataSourceCompleted loadMoreDataSourceCompleted;

 @property (nonatomic,copy) loadImagesForVisiableRowsFunc loadImagesForVisiableRowsFunc;
 @property (nonatomic,copy) appImageDownloadCompleted appImageDownloadCompleted;

对于上提加载更多、下拉刷新、图片异步加载这几个功能都是可选的，它们以组件的形式存在。比如，在实例化该controller的时候你就可以设置上提和下拉是否可用。而对于图片下载，你只要不实现其相应得block，它也不会对你造成额外的负担。

 - (id)initWithRefreshHeaderViewEnabled:(BOOL)enableRefreshHeaderView
 andLoadMoreFooterViewEnabled:(BOOL)enableLoadMoreFooterView;

 - (id)initWithRefreshHeaderViewEnabled:(BOOL)enableRefreshHeaderView
           andLoadMoreFooterViewEnabled:(BOOL)enableLoadMoreFooterView
                      andTableViewFrame:(CGRect)frame;

 #pragma mark - UITableView Delegate -
 - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{
     if (nil==self.dataSource) {
         return 0;
     }

     return [self.dataSource count];
 }

 - (UITableViewCell*)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
     if (!self.cellForRowAtIndexPathDelegate) {
         @throw [NSException exceptionWithName:@"Framework Error"
                                        reason:@"Must be setting cellForRowAtIndexPathBlock for UITableView" userInfo:nil];
     }
     return self.cellForRowAtIndexPathDelegate(tableView,indexPath);
 }

 - (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath{
     if (!self.heightForRowAtIndexPathDelegate) {
         @throw [NSException exceptionWithName:@"Framework Error"
                                        reason:@"Must be setting heightForRowAtIndexPathDelegate for UITableView" userInfo:nil];
     }
     return self.heightForRowAtIndexPathDelegate(tableView,indexPath);
 }

 - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
     if (self.didSelectRowAtIndexPathDelegate) {
         self.didSelectRowAtIndexPathDelegate(tableView,indexPath);
     }
 }

 #pragma mark - LoadMoreTableFooterDelegate Methods -
 - (void)loadMoreTableFooterDidTriggerRefresh:(LoadMoreTableFooterView *)view{
     if (self.loadMoreDataSourceFunc&&self.loadMoreDataSourceCompleted) {
         self.loadMoreDataSourceFunc();

         double delayInSeconds = 3.0;
         dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
         dispatch_after(popTime, dispatch_get_main_queue(),
                        self.loadMoreDataSourceCompleted);
     }
 }

 - (BOOL)loadMoreTableFooterDataSourceIsLoading:(LoadMoreTableFooterView *)view{
     return self.isLoadingMore;
 }

 #pragma mark - EGORefreshTableHeaderDelegate Methods -
 -(void)egoRefreshTableHeaderDidTriggerRefresh:(EGORefreshTableHeaderView *)view{
     if (self.refreshDataSourceFunc&&self.refreshDataSourceCompleted){
         self.refreshDataSourceFunc();

         double delayInSeconds = 3.0;
         dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
         dispatch_after(popTime, dispatch_get_main_queue(),
                        self.refreshDataSourceCompleted);
     }
 }

 -(BOOL)egoRefreshTableHeaderDataSourceIsLoading:(EGORefreshTableHeaderView *)view{
     return self.isRefreshing;
 }

 -(NSDate *)egoRefreshTableHeaderDataSourceLastUpdated:(EGORefreshTableHeaderView *)view{
     return [NSDate date];
 }

 #pragma mark - UIScrollViewDelegate Methods -
 -(void)scrollViewWillBeginDecelerating:(UIScrollView *)scrollView{
     self.currentOffsetPoint=scrollView.contentOffset;
 }

 -(void)scrollViewDidScroll:(UIScrollView *)scrollView{
     CGPoint pt=scrollView.contentOffset;
     if (self.currentOffsetPoint.y<pt.y) {
         [self.loadMoreFooterView loadMoreScrollViewDidScroll:scrollView];
     }else {
         [self.refreshHeaderView egoRefreshScrollViewDidScroll:scrollView];
     }
 }

 -(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{
     CGPoint pt=scrollView.contentOffset;
     if (self.currentOffsetPoint.y<pt.y) {
         [self.loadMoreFooterView loadMoreScrollViewDidEndDragging:scrollView];
     }else {
         [self.refreshHeaderView egoRefreshScrollViewDidEndDragging:scrollView];
     }

     if (!decelerate&&self.loadImagesForVisiableRowsFunc) {
         self.loadImagesForVisiableRowsFunc();
     }
 }

 -(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{
     if (self.loadImagesForVisiableRowsFunc) {
         self.loadImagesForVisiableRowsFunc();
     }
 }

 #pragma mark - download image async -
 -(void)appImageDidLoad:(NSIndexPath *)indexPath{
     if (self.appImageDownloadCompleted) {
         self.appImageDownloadCompleted(indexPath);
     }
 }

ELTableViewController 的使用

创建一个新的controller继承自：ELTableViewController；

override父类的initBlocks方法：

 #pragma mark - private methods -
 - (void)loadDataSource{
     self.dataSource=[NSMutableArray array];
     [self.dataSource addObject:@"dataSource_1"];
     [self.dataSource addObject:@"dataSource_2"];
     [self.dataSource addObject:@"dataSource_3"];
     [self.dataSource addObject:@"dataSource_4"];
     [self.dataSource addObject:@"dataSource_5"];
     [self.dataSource addObject:@"dataSource_6"];
     [self.dataSource addObject:@"dataSource_7"];
     [self.dataSource addObject:@"dataSource_8"];
     [self.dataSource addObject:@"dataSource_9"];
     [self.dataSource addObject:@"dataSource_10"];
 }

 - (void)initBlocks{
     __block TestViewController *blockedSelf=self;

     //load more
     self.loadMoreDataSourceFunc=^{
         [blockedSelf.dataSource addObject:@"loadMoreDataSourceBlock_1"];
         [blockedSelf.dataSource addObject:@"loadMoreDataSourceBlock_2"];
         [blockedSelf.dataSource addObject:@"loadMoreDataSourceBlock_3"];
         [blockedSelf.dataSource addObject:@"loadMoreDataSourceBlock_4"];
         [blockedSelf.dataSource addObject:@"loadMoreDataSourceBlock_5"];

         blockedSelf.isLoadingMore=YES;
         [self.tableView reloadData];

         NSLog(@"loadMoreDataSourceBlock was invoked");
     };

     //load more completed
     self.loadMoreDataSourceCompleted=^{
         blockedSelf.isLoadingMore=NO;
         [blockedSelf.loadMoreFooterView loadMoreScrollViewDataSourceDidFinishedLoading:self.tableView];

         NSLog(@"after loadMore completed");
     };

     //refresh
     self.refreshDataSourceFunc=^{
         blockedSelf.dataSource=[NSMutableArray array];
         [blockedSelf.dataSource addObject:@"refreshDataSourceBlock_1"];
         [blockedSelf.dataSource addObject:@"refreshDataSourceBlock_2"];
         [blockedSelf.dataSource addObject:@"refreshDataSourceBlock_3"];
         [blockedSelf.dataSource addObject:@"refreshDataSourceBlock_4"];
         [blockedSelf.dataSource addObject:@"refreshDataSourceBlock_5"];

         blockedSelf.isRefreshing=YES;
         [self.tableView reloadData];

         NSLog(@"refreshDataSourceBlock was invoked");
     };

     //refresh completed
     self.refreshDataSourceCompleted=^{
         blockedSelf.isRefreshing=NO;
         [blockedSelf.loadMoreFooterView loadMoreScrollViewDataSourceDidFinishedLoading:self.tableView];

         NSLog(@"after refresh completed");
     };

     self.cellForRowAtIndexPathDelegate=^(UITableView *tableView, NSIndexPath *indexPath){
         static NSString *cellIdentifier=@"cellIdentifier";
         UITableViewCell *cell=[tableView dequeueReusableCellWithIdentifier:cellIdentifier];
         if (!cell) {
             cell=[[[UITableViewCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier]autorelease];
         }

         cell.textLabel.text=[blockedSelf.dataSource objectAtIndex:indexPath.row];

         NSLog(@"block:cellForRowAtIndexPathBlock has been invoked.");

         return cell;
     };

     self.heightForRowAtIndexPathDelegate=^(UITableView *tableView, NSIndexPath *indexPath){
         NSLog(@"block:heightForRowAtIndexPathBlock has been invoked.");
         return 60.0f;
     };

     self.didSelectRowAtIndexPathDelegate=^(UITableView *tableView, NSIndexPath *indexPath){
         NSLog(@"block:didSelectRowAtIndexPathDelegate has been invoked.");
     };

 }