NSURLConnection实现断点续传下载

常用类NSURL：//请求地址NSURLRequest： //一个NSURLRequest对象就代表一个请求，它包含的信息有:一个NSURL对象请求方法、请求头、请求体请求超时… …NSMutableURLRequest：发送NSURLRequest的数据给服务器，并收集来自服务器的响应数据NSURLConnection的使用步骤

使用NSURLConnection发送请求的步骤很简单 创建一个NSURL对象，设置请求路径 传入NSURL创建一个NSURLRequest对象，设置请求头和请求体 使用NSURLConnection发送NSURLRequest

NSURLConnection发送请求

NSURLConnection常见的发送请求方法有以下几种 同步请求

+ (NSData *)sendSynchronousRequest:(NSURLRequest *)request returningResponse:(NSURLResponse **)response error:(NSError **)error;

异步请求：根据对服务器返回数据的处理方式的不同，又可以分为2种 block回调

+ (void)sendAsynchronousRequest:(NSURLRequest*) requestqueue:(NSOperationQueue*) queuecompletionHandler:(void (^)(NSURLResponse* response, NSData* data, NSError* connectionError)) handler;代理- (id)initWithRequest:(NSURLRequest *)request delegate:(id)delegate;+ (NSURLConnection*)connectionWithRequest:(NSURLRequest *)request delegate:(id)delegate;- (id)initWithRequest:(NSURLRequest *)request delegate:(id)delegate startImmediately:(BOOL)startImmediately;在startImmediately = NO的情况下，需要调用start方法开始发送请求- (void)start;成为NSURLConnection的代理，最好遵守NSURLConnectionDataDelegate协议NSURLConnectionDataDelegate代理方法//开始接收到服务器的响应时调用- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response;//接收到服务器返回的数据时调用（服务器返回的数据比较大时会调用多次）- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;//服务器返回的数据完全接收完毕后调用- (void)connectionDidFinishLoading:(NSURLConnection *)connection;//请求出错时调用（比如请求超时）- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;NSMutableURLRequest可变URL请求

NSMutableURLRequest是NSURLRequest的子类，常用方法有

//设置请求超时等待时间（超过这个时间就算超时，请求失败）- (void)setTimeoutInterval:(NSTimeInterval)seconds;//设置请求方法（比如GET和POST）- (void)setHTTPMethod:(NSString *)method;//设置请求体- (void)setHTTPBody:(NSData *)data;//设置请求头- (void)setValue:(NSString *)value forHTTPHeaderField:(NSString *)field;创建GET和POST请求//创建GET请求NSString *urlStr = [@”http://192.168.1.102:8080/Server/login?username=123&pwd=123″ stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];NSURL *url = [NSURL URLWithString:urlStr];NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];//创建POST请求NSString *urlStr = @”http://192.168.1.102:8080/Server/login”;NSURL *url = [NSURL URLWithString:urlStr];NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];request.HTTPMethod = @”POST”;// 请求体NSString *bodyStr = @”username=123&pwd=123″;request.HTTPBody = [bodyStr dataUsingEncoding:NSUTF8StringEncoding];断点续传下载实例#import “ViewController.h”#ViewController () <NSURLConnectionDataDelegate>- (IBAction)download:(UIButton *)sender;/** * 用来写数据的文件句柄对象 */@property (nonatomic, strong) NSFileHandle *writeHandle;/** * 文件的总大小 */@property (nonatomic, assign) long long totalLength;/** * 当前已经写入的文件大小 */@property (nonatomic, assign) long long currentLength;/** * 连接对象 */@property (nonatomic, strong) NSURLConnection *conn;@property (nonatomic, weak) DACircularProgressView *circleView;@end@implementation ViewController- (void)viewDidLoad{[super viewDidLoad];// Do any additional setup after loading the view, typically from a nib.DACircularProgressView *circleView = [[DACircularProgressView alloc] init];circleView.frame = CGRectMake(100, 50, 100, 100);circleView.progressTintColor = [UIColor redColor];circleView.trackTintColor = [UIColor blueColor];circleView.progress = 0.0000001;[self.view addSubview:circleView];self.circleView = circleView;}#pragma mark – NSURLConnectionDataDelegate代理方法/** * 请求失败时调用（请求超时、网络异常） * * @param error错误原因 */- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{NSLog(@”didFailWithError”);}/** * 1.接收到服务器的响应就会调用 * * @param response 响应 */- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{if (self.currentLength) return;// 文件路径NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];NSString *filepath = [caches stringByAppendingPathComponent:@”videos.zip”];// 创建一个空的文件 到 沙盒中NSFileManager *mgr = [NSFileManager defaultManager];[mgr createFileAtPath:filepath contents:nil attributes:nil];// 创建一个用来写数据的文件句柄self.writeHandle = [NSFileHandle fileHandleForWritingAtPath:filepath];// 获得文件的总大小self.totalLength = response.expectedContentLength;}/** * 2.当接收到服务器返回的实体数据时调用（具体内容，，这个方法可能会被调用多次） * * @param data这次返回的数据 */- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{// 移动到文件的最后面[self.writeHandle seekToEndOfFile];// 将数据写入沙盒[self.writeHandle writeData:data];// 累计文件的长度self.currentLength += data.length;self.circleView.progress = (double)self.currentLength/ self.totalLength;}/** * 3.加载完毕后调用（服务器的数据已经完全返回后） */- (void)connectionDidFinishLoading:(NSURLConnection *)connection{self.currentLength = 0;self.totalLength = 0;// 关闭文件[self.writeHandle closeFile];self.writeHandle = nil;}- (IBAction)download:(UIButton *)sender {// 状态取反sender.selected = !sender.isSelected;(sender.selected) { // 继续（开始）下载// 1.URLNSURL *url = [NSURL URLWithString:@”http://localhost:8080/MJServer/resources/videos.zip”];// 2.请求NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];// 设置请求头NSString *range = [NSString stringWithFormat:@”bytes=%lld-“, self.currentLength];[request setValue:range forHTTPHeaderField:@”Range”];// 3.下载(创建完conn对象后，会自动发起一个异步请求)self.conn = [NSURLConnection connectionWithRequest:request delegate:self];} else { // 暂停[self.conn cancel];self.conn = nil;}}@endNSURLConnection小结1.发布异步请求01–block回调+ (:(void (^)(NSURLResponse* response, NSData* data, NSError* connectionError)) handler//request : 需要发送的请求//queue : 一般用主队列，存放handler这个任务//handler : 当请求完毕后，会自动调用这个block2.利用NSURLConnection发送请求的基本步骤:@”http://4234324/5345345″];];3> 发送请求[: ^(NSURLResponse *response, NSData *data, NSError *connectionError) {4> 处理服务器返回的数据 }];

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