//下载文件

+(void)downloadTask:(NSString*)urlStr  progress:(void (^)(NSProgress * _Nonnull downloadProgress))progress completionHandler:(void(^)(NSURLResponse * _Nonnull response, NSURL * _Nullable filePath, NSError * _Nullable error, NSString *pathFile))completionHandler{
    
    if (urlStr.length == 0) {
        return;
    }
    
    //保存路径
    NSArray *arr = [urlStr componentsSeparatedByString:@"/"];
    NSString *fileName = arr.lastObject;
    // 沙盒文件路径
    NSString *path = [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:fileName];
    NSLog(@"File downloaded to: %@",path);
    
    //1.创建管理者对象
    AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
    //2.确定请求的URL地址
    NSURL *url = [NSURL URLWithString:urlStr];
    //3.创建请求对象
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    //4.下载任务
    NSURLSessionDownloadTask *task = [manager downloadTaskWithRequest:request progress:^(NSProgress * _Nonnull downloadProgress) {
        //打印下下载进度
        NSLog(@"downloadProgress = %@",downloadProgress);
        if(progress){
            progress(downloadProgress);
        }
    } destination:^NSURL * _Nonnull(NSURL * _Nonnull targetPath, NSURLResponse * _Nonnull response) {
        //设置文件保存路径
        NSLog(@"path = %@",[NSURL fileURLWithPath:path]);
        return [NSURL fileURLWithPath:path];
    } completionHandler:^(NSURLResponse * _Nonnull response, NSURL * _Nullable filePath, NSError * _Nullable error) {
        NSLog(@"完成cache：%@",filePath);

        if(error == nil){//下载完成
            if(completionHandler){
                completionHandler(response,filePath,error,path);
            }
        }else{
            NSString *message = nil;
            if(error.code == -1005){
                message = @"网络异常";
            }else if(error.code == -1001){
                message = @"请求超时";
            }else{
                message = @"未知错误";
            }
            NSLog(@"message:%@",message);
            if(completionHandler){
                completionHandler(response,filePath,error,@"");
            }
        }
        
    }];
    //5.开始启动下载任务
    [task resume];
}

https://blog.csdn.net/fuzongjian/article/details/51325581