非同步下載

- (void)downloadWithUrl:(NSString*)targetURL
{
    NSString *urlAsString = targetURL;
    NSURL *url = [NSURL URLWithString:urlAsString];
    NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url];
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
   
    [NSURLConnection sendAsynchronousRequest:urlRequest queue:queue completionHandler:^(NSURLResponse *responce, NSData *data, NSError *error) {
        if ([data length] > 0 && error == nil) {
            //取得文件目錄
            NSString* documentsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentationDirectory, NSUserDomainMask, YES) objectAtIndex:0];
            //完整檔案路徑
            NSString* filePath = [documentsDir stringByAppendingString:@"ht-inception-360p.mp4"];
            //將資料寫入檔案
            [data writeToFile:filePath atomically:YES];
           
            NSLog(@"成功存檔至%@",filePath);
        }
        else if ([data length] == 0 && error == nil){
            NSLog(@"沒有被下載");
        }
        else if (error != nil){
            NSLog(@"Err : %@",error);
        }
    }];

}

//判斷檔案是否存在
   
    if (![[NSFileManager defaultManager] fileExistsAtPath:@"/你的本地端位置/檔名.mp4"]){
        NSLog(@"檔名.mp4不存在");
    }else{
        NSLog(@"檔名.mp4存在");
    }