iosUITableView封装之下拉-上提-图片异步加载



# 写在前面

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.");
};

}

然后在ViewDidLoad中调用:
[self initBlocks];
[self loadDataSource];
[self.tableView reloadData];


最后,你在实例化该controller的时候,可以指定是否使用上提和下拉
self.viewController = [[[TestViewController alloc] initWithRefreshHeaderViewEnabled:YES andLoadMoreFooterViewEnabled:YES]autorelease];


# 写在最后

写完之后,我用它重构了一下快易博中,新浪微博的几个视图。也省掉了一些冗余代码,如果当初在开发的时候就使用它的话,感觉还是省了一些功夫的。

它其实也还是比较简单的封装,所以还不是很具有业务相关性,同时也可见它还有很多可继续增强的功能:

1、  封装增删改查功能

2、  封装加载、操作时动画

3、  封装网络加载的统一实现

……………….
先写到这里吧。

推荐两篇讲ios block非常不错的文章:

http://lldong.github.com/blog/2011/12/30/blocks/

http://yannickloriot.com/2011/11/working-with-blocks/

源码地址:

https://github.com/yanghua/ELTableViewController



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