#import "ViewController.h" @interface ViewController ()<NSURLConnectionDataDelegate> @property (weak, nonatomic) IBOutlet UIProgressView *progressView; @property (nonatomic, assign) NSInteger totalSize; @property (nonatomic, assign) NSInteger currentSize; /** 文件句柄*/ @property (nonatomic, strong)NSFileHandle *handle; /** 沙盒路径 */ @property (nonatomic, strong) NSString *fullPath; /** 连接对象 */ @property (nonatomic, strong) NSURLConnection *connect; @end @implementation ViewController - (IBAction)startBtnClick:(id)sender { [self download]; } - (IBAction)cancelBtnClick:(id)sender { [self.connect cancel]; } - (IBAction)goOnBtnClick:(id)sender { [self download]; } //内存飙升 -(void)download { //1.url // NSURL *url = [NSURL URLWithString:@"http://imgsrc.baidu.com/forum/w%3D580/sign=54a8cc6f728b4710ce2ffdc4f3cec3b2/d143ad4bd11373f06c0b5bd1a40f4bfbfbed0443.jpg"]; NSURL *url = [NSURL URLWithString:@"http://www.33lc.com/article/UploadPic/2012-10/2012102514201759594.jpg"]; //2.创建请求对象 NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url]; //设置请求头信息,告诉服务器值请求一部分数据range /* bytes=0-100 bytes=-100 bytes=0- 请求100之后的所有数据 */ NSString *range = [NSString stringWithFormat:@"bytes=%zd-",self.currentSize]; [request setValue:range forHTTPHeaderField:@"Range"]; NSLog(@"+++++++%@",range); //3.发送请求 NSURLConnection *connect = [[NSURLConnection alloc]initWithRequest:request delegate:self]; self.connect = connect; } #pragma mark ---------------------- #pragma mark NSURLConnectionDataDelegate -(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response { NSLog(@"didReceiveResponse"); //1.得到文件的总大小(本次请求的文件数据的总大小 != 文件的总大小) // self.totalSize = response.expectedContentLength + self.currentSize; if (self.currentSize >0) { return; } self.totalSize = response.expectedContentLength; //2.写数据到沙盒中 self.fullPath = [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject]stringByAppendingPathComponent:@"123.jpg"]; NSLog(@"%@",self.fullPath); //3.创建一个空的文件 [[NSFileManager defaultManager] createFileAtPath:self.fullPath contents:nil attributes:nil]; //NSDictionary *dict = [[NSFileManager defaultManager]attributesOfItemAtPath:self.fullPath error:nil]; //4.创建文件句柄(指针) self.handle = [NSFileHandle fileHandleForWritingAtPath:self.fullPath]; } -(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { //1.移动文件句柄到数据的末尾 [self.handle seekToEndOfFile]; //2.写数据 [self.handle writeData:data]; //3.获得进度 self.currentSize += data.length; //进度=已经下载/文件的总大小 NSLog(@"%f",1.0 * self.currentSize/self.totalSize); self.progressView.progress = 1.0 * self.currentSize/self.totalSize; //NSLog(@"%@",self.fullPath); } -(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error { } -(void)connectionDidFinishLoading:(NSURLConnection *)connection { //1.关闭文件句柄 [self.handle closeFile]; self.handle = nil; NSLog(@"connectionDidFinishLoading"); NSLog(@"%@",self.fullPath); } @end
#####6.0 大文件断点下载
（1）实现思路
在下载文件的时候不再是整块的从头开始下载，而是看当前文件已经下载到哪个地方，然后从该地方接着往后面下载。可以通过在请求对象中设置请求头实现。
（2）解决方案（设置请求头）
```
//2.创建请求对象
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
//2.1 设置下载文件的某一部分
// 只要设置HTTP请求头的Range属性, 就可以实现从指定位置开始下载
/*
表示头500个字节：Range: bytes=0-499
表示第二个500字节：Range: bytes=500-999
表示最后500个字节：Range: bytes=-500
表示500字节以后的范围：Range: bytes=500-
*/
NSString *range = [NSString stringWithFormat:@"bytes=%zd-",self.currentLength];
[request setValue:range forHTTPHeaderField:@"Range"];
```
（3）注意点（下载进度并判断是否需要重新创建文件）
```objc
//获得当前要下载文件的总大小（通过响应头得到）
NSHTTPURLResponse *res = (NSHTTPURLResponse *)response;
//注意点：res.expectedContentLength获得是本次请求要下载的文件的大小（并非是完整的文件的大小）
//因此：文件的总大小 == 本次要下载的文件大小+已经下载的文件的大小
self.totalLength = res.expectedContentLength + self.currentLength;
NSLog(@"----------------------------%zd",self.totalLength);
//0 判断当前是否已经下载过，如果当前文件已经存在，那么直接返回
if (self.currentLength >0) {
return;
}
```