学步园

这里只是说说异步 单线程下载与文件的保存
以下载一个mp3文件并保存为例：

-(void)loading
{
    //设置文件下载地址 
    NSString *urlString = [NSString stringWithFormat:@"http://zhangmenshiting2.baidu.com/data2/music/14893666/14893666.mp3?xcode=f7e142418de081ff52f81344843b869a&mid=0.73830637514858"];//这里设置的是一个mp3的下载地址
    NSString * encodedString = (NSString *)CFURLCreateStringByAddingPercentEscapes( kCFAllocatorDefault, (CFStringRef)urlString, NULL, NULL,  kCFStringEncodingUTF8 );
    NSURL *url =[NSURL URLWithString:encodedString];
    
    //创建NSURLRequest和NSURLConnection，并立即启动连接
    NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData timeoutInterval:5.0f];
    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:YES];
   if (connection) 
    {            
		  self.receivedData = [NSMutableData data];//初始化接收数据的缓存
    } 
     else 
     {
                      NSLog(@"Bad Connection!");
      }

    [request release];
    [connection release];
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    [receivedData setLength:0];//置空数据
    long long mp3Size = [response expectedContentLength];//获取要下载的文件的长度
    NSLog(@"%lld",mp3Size);

 }

//接收NSMutableData数据
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data 
{
    [receivedData appendData:data];
}

//接收完毕
- (void)connectionDidFinishLoading:(NSURLConnection *)connection 
{
    [connection cancel];
 //在保存文件和播放文件之前可以做一些判断，保证程序的健壮行：例如：文件是否存在，接收的数据是否完整等处理，此处没加，使用时注意
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);    
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSLog(@"mp3 path=%@",documentsDirectory);    
    NSString *filePath = [documentsDirectory stringByAppendingPathComponent: mp3Name];//mp3Name:你要保存的文件名称，包括文件类型。如果你知道文件类型的话，可以指定文件类型；如果事先不知道文件类型，可以在- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response中获取要下载的文件类型
    
    //在document下创建文件
    NSFileManager *fileManager = [NSFileManager defaultManager]; 
    [fileManager createFileAtPath:filePath contents:nil attributes:nil];
    NSLog(@"mp3 path=%@",filePath);
    //将下载的数据，写入文件中
    [receivedData writeToFile:filePath atomically:YES];

   //播放下载下来的mp3文件
    [self playVoice:filePath];

   
  //如果下载的是图片则可以用下面的方法生成图片并显示 create image from data and set it to ImageView
   /*
     UIImage *image = [[UIImage alloc] initWithData:recvData];
    [imgView setImage:image];
    */
}   

简单的播放mp3文件的方法：
使用前要添加库：AudioToolbox.framework和AVFoundation.framework，
//添加头文件
#import <AVFoundation/AVFoundation.h>
#import <AudioToolbox/AudioToolbox.h>
-(void)playVoice:(NSString *)filePath
{
    //播放文件的路径
    NSURL * musicURL= [[NSURL alloc] initFileURLWithPath:filePath];  

    //创建音频 播放器
    AVAudioPlayer * voicePlayer  = [[AVAudioPlayer alloc] initWithContentsOfURL:musicURL error:nil];
    self.thePlayer = voicePlayer;
    [voicePlayer release];
  
    [musicURL release];
    [thePlayer setVolume:1];   //设置音量大小
    thePlayer.numberOfLoops = -1;//设置音乐播放次数  -1为一直循环
    
   //播放mp3，如果想要实现一些别的功能，可以看看AVAudioPlayer这个类，这里只是实现播放功能
     [thePlayer play];
}