NSURLSession中的downloadTask的使用

1.用downloadTask下載圖片

優點：簡單

缺點：不能監聽下載的進度

代碼示例：

    NSURL *url = [NSURL URLWithString:@"http://pic1.win4000.com/pic/b/03/21691230681.jpg"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    
    NSURLSession *session = [NSURLSession sharedSession];
    NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithRequest:request completionHandler:^(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error) {
       //默認把數據寫到磁盤中：tmp/...隨時可能被刪除
        NSLog(@"location= %@", location);
        
        //轉移文件
        NSString *cache = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)  lastObject];
        NSString *filePath = [cache stringByAppendingPathComponent:response.suggestedFilename];
        NSLog(@"filePath = %@",filePath);
        NSURL *toURL = [NSURL fileURLWithPath:filePath];
        [[NSFileManager defaultManager] moveItemAtURL:location toURL:toURL error:nil];
    }];
    [downloadTask resume];

 

2.downloadTask下載比較大的文件

優點：已經解決內存飈升的問題

缺點：無法實現斷點下載的功能

代碼如下：

#import "ViewController.h"

@interface ViewController ()<NSURLSessionDownloadDelegate>

@property (nonatomic,strong) NSURLSession *session;
@property (nonatomic,strong) NSURLSessionDownloadTask *downloadTask;
@property (nonatomic,strong) NSData *resumeData ;

@end

@implementation ViewController

- (IBAction)startClick:(id)sender {
    
    [self.downloadTask resume];
}

- (IBAction)suspendClick:(id)sender {
    [self.downloadTask suspend];
}

- (IBAction)cancleClick:(id)sender {
    //用cancel的方法，操作不可以恢復
//    [self.downloadTask cancel];
    
    //取消，可以恢復的取消操作
    //resumeDta可以用來恢復下載的數據
    [self.downloadTask cancelByProducingResumeData:^(NSData * _Nullable resumeData) {
        //data不是沙盒中已經下載好的數據
        self.resumeData = resumeData;
    }];
    
    self.downloadTask = nil;
}

- (IBAction)resumeClick:(id)sender {
    //在恢復下載的時候，判斷是否可以用來進行恢復下載的數據，如果有那么就根據該數據創建一個新的網絡請求
    if (self.resumeData) {
        //取消 再恢復，在恢復的時候，需要重新創建
        self.downloadTask = [self.session downloadTaskWithResumeData:self.resumeData];
    }
    [self.downloadTask resume];
}

- (NSURLSession *)session {
    if (!_session) {
        _session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[NSOperationQueue mainQueue]];
    }
    return _session;
}

- (NSURLSessionDownloadTask *)downloadTask {
    if (!_downloadTask) {
        NSURL *url = [NSURL URLWithString:@"http://meiye-mbs.oss-cn-shenzhen.aliyuncs.com/mbsFiles/0e3d0e4a0d5d4da5963e9e7617e8de101565841097849.mp4"];
        NSURLRequest *request = [NSURLRequest requestWithURL:url];
        _downloadTask = [self.session downloadTaskWithRequest:request];
    }
    return _downloadTask;
}

#pragma mark - 代理
//01 寫數據的時候調用
/**
 bytesWritten:本次寫入的數據大小
 totalBytesWritten：寫入數據的總大小
 totalBytesExpectedToWrite:文件的總大小
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite {
    NSLog(@"111111=%f", 1.0 * totalBytesWritten / totalBytesExpectedToWrite);
}

//02 下載完成的時候調用
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location {
    //轉移文件
    NSString *cache = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)  lastObject];
    NSString *filePath = [cache stringByAppendingPathComponent:downloadTask.response.suggestedFilename];
    NSLog(@"filePath = %@",filePath);
    NSURL *toURL = [NSURL fileURLWithPath:filePath];
    [[NSFileManager defaultManager] moveItemAtURL:location toURL:toURL error:nil];
}

//03  整個請求結束或者失敗的時候調用
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
    NSLog(@"結束");
}
@end