NSURLConnection下载显示进度

1、创建一个NSURLConnection对象：

NSURL*url=[NSURLURLWithString:@"http://119.147.106.249/gdown_group11/M00/3F/15/d5Nq-UxBq88AAAAAAUn8QBO4rlY4306605/01_01_Android%E5%B9%B3%E5%8F%B0%E4%B8%80%E6%97%A5%E6%B8%B8.mp4?k=-4hoIXm9CXQ_Zo79EQprcQ&t=1346820047&u=3662410469-66934941-bei9apjt&s=307200&file=01_01_Android%E5%B9%B3%E5%8F%B0%E4%B8%80%E6%97%A5%E6%B8%B8.mp4"];

    NSURLRequest*request=[[NSURLRequestalloc]initWithURL:urlcachePolicy:NSURLRequestReloadIgnoringCacheDatatimeoutInterval:100.0];//设置缓存和超时

    NSURLConnection*connection=nil;

    connection=[[NSURLConnectionalloc]initWithRequest:requestdelegate:selfstartImmediately:YES];

//初始化connection对象并马上执行，有的初始化方法并不是马上开始执行，而需要调用start方法。

二、实现connection的回调方法：

-(void)connection:(NSURLConnection*)connectiondidReceiveResponse:(NSURLResponse*)response

{//该方法在响应connection时调用

    NSLog(@"response");

    self.data=[[NSMutableDataalloc]init];

    NSHTTPURLResponse*httpResponse=(NSHTTPURLResponse*)response;

    if(httpResponse&&[httpResponserespondsToSelector:@selector(allHeaderFields)]){

        NSDictionary*httpResponseHeaderFields=[httpResponseallHeaderFields];

        mFileSize=[[httpResponseHeaderFieldsobjectForKey:@"Content-Length"]longLongValue];

    }//获取文件文件的大小

}

-(void)connection:(NSURLConnection*)connectiondidFailWithError:(NSError*)error

{//出错时调用

    NSLog(@"error");

}

-(void)connection:(NSURLConnection*)connectiondidReceiveData:(NSData*)data

{//接受数据，在接受完成之前，该方法重复调用

    NSLog(@"receive");

    [_dataappendData:data];

    _displayLabel.text=[NSStringstringWithFormat:(@"%6.1fkb/%6.1fkb"),[_datalength]/1024.0,mFileSize/1024.0];

    [_progressViewsetProgress:[_datalength]/(float)mFileSize];

}

-(void)connectionDidFinishLoading:(NSURLConnection*)connection

{//完成时调用

    NSLog(@"Finish");

    NSString*filePath=[[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask,YES)objectAtIndex:0]stringByAppendingPathComponent:@"android.mp4"];

    [_datawriteToFile:filePathatomically:NO];//将数据写入Documents目录。

    NSLog(@"%@",filePath);

}