在nsurlconnection中恢复下载功能

从本质上说,您不能暂停,但可以取消连接,然后创建一个新连接以恢复旧连接中断的位置。但是,要连接的服务器必须支持范围头。将其设置为“bytes=size\u already\u downloaded-”,它应该会在您取消它的地方出现。

要继续下载并获取文件的其余部分,可以设置 Range 通过执行以下操作在http请求头中设置值:

- (void)downloadFromUrl:(NSURL*)url toFilePath:(NSString *)filePath {

    NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url     cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:10];
    if (!request) {
        NSLog(@"Error creating request");
        // Do something
    }
    [request setHTTPMethod:@"GET"];

    // Add header to existing file
    NSFileManager *fm = [NSFileManager defaultManager];
    if([fm fileExistsAtPath:filePath]) {
        NSError *error = nil;      
        NSDictionary * fileProp = [fm attributesOfItemAtPath:filePath error:&error];
        if (error) {
            NSLog(@"Error: %@", [error localizedDescription]);
            // Do something
        } else {
            // Set header to resume 
            long long fileSize = [[fileProp objectForKey:@"NSFileSize"]longLongValue];
            NSString *range = @"bytes=";
            range = [[range stringByAppendingString:[[NSNumber numberWithLongLong:fileSize] stringValue]] stringByAppendingString:@"-"];
            [request setValue:range forHTTPHeaderField:@"Range"];
        }
    }
    NSURLConnection * connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];

    if (!connection) {
        NSLog(@"Connection failed.");
        // Do something
    }
}

你也可以用 - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response 要通过检查预期大小检查现有文件是否已完全下载,请执行以下操作: [response expectedContentLength]; . 如果大小匹配,则可能需要取消连接。