IOS开发网络篇之──ASIHTTPRequest下载示例（支持断点续传）

一、创建网络请求队列

首先，创建网络请求队列，如下：
ASINetworkQueue   *que = [[ASINetworkQueue alloc] init];
self.netWorkQueue = que;
[que release];

[self.netWorkQueue reset];
[self.netWorkQueue setShowAccurateProgress:YES];
[self.netWorkQueue go];

二、创建存放路径

//初始化Documents路径
NSString *path = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
//初始化临时文件路径
NSString *folderPath = [path stringByAppendingPathComponent:@"temp"];
//创建文件管理器
NSFileManager *fileManager = [NSFileManager defaultManager];
//判断temp文件夹是否存在
BOOL fileExists = [fileManager fileExistsAtPath:folderPath];

if (!fileExists) {//如果不存在说创建,因为下载时,不会自动创建文件夹
[fileManager createDirectoryAtPath:folderPath 
           withIntermediateDirectories:YES 
                            attributes:nil
                                 error:nil];
}

三、发送下载请求

这里对下面几个对象说明一下：CustomCell是我自定义的cell，cell上面有下载和暂停两个按钮，其tag值为cell所在的行，因此这里的[sendertag]为下载按钮的tag值，self.downloadArray为array数组对象，存放要下载的资源字典信息，在该字典中有一键为URL，它对应的值就是我们下载链接。
这些东西，根据自己的实际需要改动一下即可使用

CustomCell *cell = (CustomCell *)[self.myTableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:[sender tag] inSection:0]];
NSString  *filePath = [[self.downloadArray objectAtIndex:[sender tag]] objectForKey:@"URL"];
NSLog(@"filePath=%@",filePath);
//初始下载路径
NSURL *url = [NSURL URLWithString:filePath];
//设置下载路径
ASIHTTPRequest *request = [[ASIHTTPRequest alloc] initWithURL:url];
//设置ASIHTTPRequest代理
request.delegate = self;
//初始化保存ZIP文件路径
NSString *savePath = [path stringByAppendingPathComponent:[NSString stringWithFormat:@"book_%d.zip",[sender tag]]];
//初始化临时文件路径
NSString *tempPath = [path stringByAppendingPathComponent:[NSString stringWithFormat:@"temp/book_%d.zip.temp",[sender tag]]];
//设置文件保存路径
[request setDownloadDestinationPath:savePath];
//设置临时文件路径
[request setTemporaryFileDownloadPath:tempPath];

//设置进度条的代理,
[request setDownloadProgressDelegate:cell];
//设置是是否支持断点下载
[request setAllowResumeForFileDownloads:YES];
//设置基本信息
[request setUserInfo:[NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:[sender tag]],@"bookID",nil]];

NSLog(@"UserInfo=%@",request.userInfo);
//添加到ASINetworkQueue队列去下载
[self.netWorkQueue addOperation:request];
//收回request
[request release];

暂停请求

这里的cell下下载时的一样，

  CustomCell *cell = (CustomCell *)[self.myTableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:[sender tag] inSection:0]];

for (ASIHTTPRequest *request in [self.netWorkQueue operations]) {
    NSInteger bookid = [[request.userInfo objectForKey:@"bookID"] intValue];//查看userinfo信息
    if ([sender tag] == bookid) {//判断ID是否匹配
        //暂停匹配对象
        [request clearDelegatesAndCancel];
    }
}

四、ASIHTTPRequestDelegate回调方法

上面已经把下载请求与暂停请求实现，点击下载时，开始下载资源；当点暂停时，下载中断；当我们再点击下载按钮时，继续下载，在第二步的
[request setAllowResumeForFileDownloads:YES]`设置是是否支持断点下载。下面要实现ASIHTTPRequestDelegate代理方法如下：
#pragma mark -
#pragma mark ASIHTTPRequestDelegate method
//ASIHTTPRequestDelegate,下载之前获取信息的方法,主要获取下载内容的大小，可以显示下载进度多少字节
- (void)request:(ASIHTTPRequest *)request didReceiveResponseHeaders:(NSDictionary *)responseHeaders {
NSLog(@"didReceiveResponseHeaders-%@",[responseHeaders valueForKey:@"Content-Length"]);
NSLog(@"contentlength=%f",request.contentLength/1024.0/1024.0);
int bookid = [[request.userInfo objectForKey:@"bookID"] intValue];
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
float tempConLen = [[userDefaults objectForKey:[NSString stringWithFormat:@"book_%d_contentLength",bookid]] floatValue];
NSLog(@"tempConLen=%f",tempConLen);
//如果没有保存,则持久化他的内容大小
if (tempConLen == 0 ) {//如果没有保存,则持久化他的内容大小
[userDefaults setObject:[NSNumber numberWithFloat:request.contentLength/1024.0/1024.0] forKey:[NSString stringWithFormat:@"book_%d_contentLength",bookid]];
}

}
//ASIHTTPRequestDelegate,下载完成时,执行的方法
- (void)requestFinished:(ASIHTTPRequest *)request {

int bookid = [[request.userInfo objectForKey:@"bookID"] intValue];
CustomCell *cell = (CustomCell *)[self.myTableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:bookid inSection:0]];
cell.downloadCompleteStatus = YES;
cell.progressView.progress = 0.0; 
}

经过上述步骤，一个支持断点续传的功能程序实现了！