网络编程（三） 下载任务，支持断点续传

实现效果图：

注意点：1.下载的文件会保存在沙盒目录下的tmp文件夹内，这个文件夹专门存储一些临时文件，我们需要在下载完成后把文件移动到自己需要的文件夹内，并修改文件的扩展名

2.有部分链接使用下载时resume data = nil;这样断点续传功能就没有用了；

在storyboard里面添加button,progressView和显示进度的label，并进行连线

ViewController.m代码

#import "ViewController.h"

@interface ViewController ()<
NSURLSessionDownloadDelegate
>
{
    NSURLSessionDownloadTask *downTask;
    NSData *myResumeData;
    NSURLSession *session;
    NSString *fielName;

}

@property (weak, nonatomic) IBOutlet UIProgressView *progressView;
@property (weak, nonatomic) IBOutlet UILabel *progressLabel;

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
}

//创建下载任务
- (IBAction)downloadAction:(id)sender
{
    if (downTask)
    {
        return;
    }
    //构造需要下载的url链接

    NSURL *url = [NSURL URLWithString:@"http://apk500.bce.baidu-mgame.com/game/883000/883227/20160127061354_oem_5004211.apk?r=1"];
    //设置保存文件名为url的最后部分
    fielName = [url lastPathComponent];
    //设置session工作类型为默认
    NSURLSessionConfiguration *sessionCf = [NSURLSessionConfiguration defaultSessionConfiguration];
    //用sessionConfig配置session
    session = [NSURLSession sessionWithConfiguration:sessionCf delegate:self delegateQueue:[NSOperationQueue mainQueue]];
    //设置任务类型
    downTask = [session downloadTaskWithURL:url];

    //发送任务请求
    [downTask resume];

}

//暂停下载任务
- (IBAction)pauseAction:(UIButton *)sender
{
    if (downTask.state == NSURLSessionTaskStateRunning)
    {
        [downTask cancelByProducingResumeData:^(NSData * _Nullable resumeData) {
            //If resume data cannot be created, the completion handler will be called with nil resumeData
            myResumeData = resumeData;
            downTask = nil;
        }];
    }

}
//恢复下载任务
- (IBAction)resumeAction:(id)sender
{
    if (myResumeData)
    {
        downTask = [session downloadTaskWithResumeData:myResumeData];
        [downTask resume];

        myResumeData = nil;
    }
}
//把下载来的文件移动到Documents文件夹下并修改扩展名
- (void)moveFileToDocuments:(NSURL *)location
{
    NSFileManager *manager = [NSFileManager defaultManager];
    NSString *newPath = [NSHomeDirectory() stringByAppendingString:[NSString stringWithFormat:@"/Documents/%@",fielName]];
    fielName = nil;
    NSLog(@"%@",newPath);

    [manager moveItemAtURL:location toURL:[NSURL fileURLWithPath:newPath] error:nil];

}

#pragma mark - NSURLSessionDownloadDelegate

//在下载完成后调用
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
    NSLog(@"%@",location);
    [self moveFileToDocuments:location];
}

//进度条相关设置
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
    float progress = (float)totalBytesWritten / totalBytesExpectedToWrite;
    self.progressView.progress = progress;
    self.progressLabel.text = [NSString stringWithFormat:@"%.2f%%", progress* 100];

}