// 執行下載檔案的方法,可以監控下載進度

- (void)downLoadAction

{

    [self.view addSubview:self.numberLabel];

// 1.建立網路管理者

AFHTTPSessionManager *manager = [AFHTTPSessionManagermanager];

// 2.目標地址

NSURL* url = [NSURLURLWithString:@"https://img-blog.csdn.net/20160520141230950?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center"];

    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    __weak StartViewController* weakSelf = self;

    __block NSString* cachesBlockStr = nil;

    NSURLSessionDownloadTask *downTask = [manager downloadTaskWithRequest:request progress:^(NSProgress* progress){

//這裡監控下載進度

        [weakSelf updateProgress

    } destination:^NSURL *(NSURL *targetPath, NSURLResponse *response) {

        NSLog(@"targetPath is %@",targetPath);

//下載的目標路徑

NSString *cachesPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];

        cachesBlockStr = cachesPath;

        //path

        NSString *path = [cachesPath stringByAppendingPathComponent:response.suggestedFilename];

        return [NSURL fileURLWithPath:path];

    } completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error) {

//檔案存在filePath下，可以讀出來放到其他檔案中，後續文章會介紹

    }];

// 3.啟動任務，resume雖說是重新開始或繼續的意思，但開始也呼叫這個函式

    [downTask resume];

}

//更新一個label，顯示百分比，label隨便放位置，或者換一個更好看的控制元件，這個隨意

-(void)updateProgress:(NSProgress*)progress{

    /*

     @property int64_t totalUnitCount;  需要下載檔案的總大小

     @property int64_t completedUnitCount; 當前已經下載的大小

     */

dispatch_async(dispatch_get_main_queue(), ^(void){

//Run UI Updates

CGFloat progressf = (CGFloat)progress.completedUnitCount/(CGFloat)(progress.totalUnitCount+1);

        _numberLabel.textColor = [UIColor whiteColor];

_numberLabel.backgroundColor = [UIColorcolorWithWhite:0.falpha:0.3];

        progressf = progressf*100;

        NSString* showStr = [NSString stringWithFormat:@"%0.f%c",progressf,'%'];

        _numberLabel.text = showStr;

    });

NSLog(@"%lld  %lld",progress.totalUnitCount,progress.completedUnitCount);

}