1. 不需要獲取文件下載進度的方法

// 此方法無法獲取到文件的下載進度，只能在結束時做響應
- (void)download {
    NSURL *url = [NSURL URLWithString:@"http://127.0.0.1/HBuilder.zip"];
    [[[NSURLSession sharedSession] downloadTaskWithURL:url completionHandler:^(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        // 當前線程， 子線程
        NSLog(@"%@", [NSThread currentThread]);
        // 當前文件位置，臨時文件，下載完成后刪除臨時文件
        NSLog(@"%@",location);
        // 將文件復制到自己想要的位置
        // 存放文件的路徑
        NSString *doc = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"Builder.zip"];
        // 復制文件
        [[NSFileManager defaultManager] copyItemAtPath:location.path toPath:doc error:NULL];
    }] resume];
}

2. 需要獲取文件下載進度

需要給NSURLSession設置代理， ViewController并實現NSURLSessionDownloadDelegate協議，根據需求重寫協議中的方法。

#import "ViewController.h"

@interface ViewController () <NSURLSessionDownloadDelegate>
@property (nonatomic, strong) NSURLSession *session;
@property (nonatomic, strong) NSURLSessionDownloadTask *downloadTask;
@property (nonatomic, strong) NSData *resumData;
@end

@implementation ViewController
// 開始下載
- (IBAction)start {
    [self download];
}

// 暫停下載
- (IBAction)pause {
    [self.downloadTask cancelByProducingResumeData:^(NSData * _Nullable resumeData) {
        // 記錄已下載的數據
        self.resumData = resumeData;
        // 把續傳數據保存到沙盒中
        NSString *path = [NSTemporaryDirectory() stringByAppendingPathComponent:@"123.tmp"];
        [self.resumData writeToFile:path atomically:YES];
        NSLog(@"%@", path);
        // 將下載任務置為空
        self.downloadTask = nil;
    }];
}

// 繼續下載
- (IBAction)resume {
    // 從沙盒中獲取續傳數據
    NSString *path = [NSTemporaryDirectory() stringByAppendingPathComponent:@"123.tmp"];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    if ([fileManager fileExistsAtPath:path]) {
        self.resumData = [NSData dataWithContentsOfFile:path];
    }
    
    if (self.resumData == nil) {
        return;
    }
    
    // 調用斷點下載方法
    self.downloadTask = [self.session downloadTaskWithResumeData:self.resumData];
    [self.downloadTask resume];
    // 將續傳數據置為空
    self.resumData = nil;
}


// 懶加載
- (NSURLSession *)session {
    if (_session == nil) {
        NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
        _session = [NSURLSession sessionWithConfiguration:config delegate:self delegateQueue:0];
    }
    return _session;
}

// 下載，設置代理，獲取進度
- (void)download {
    NSURL *url = [NSURL URLWithString:@"http://127.0.0.1/HBuilder.zip"];
    self.downloadTask = [self.session downloadTaskWithURL:url];
    // 開始下載
    [self.downloadTask resume];
}

// 寫數據
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite {
    float process = totalBytesWritten * 1.0 / totalBytesExpectedToWrite;
    NSLog(@"%f", process);
}

// 斷點下載數據
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes {
    NSLog(@"續傳");
}

// 下載完成
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location {
    NSLog(@"%@", [NSThread currentThread]);
    NSLog(@"下載完成 %@", location);
}

@end