1.模态打开系统自带的系统文件 选取文件
UIDocumentPickerViewController *documentPickerVC = [[UIDocumentPickerViewController alloc] initWithURL:[NSURL fileURLWithPath:fullPath] inMode:UIDocumentPickerModeExportToService];
// 设置代理
documentPickerVC.delegate = self;
// 设置模态弹出方式
documentPickerVC.modalPresentationStyle = UIModalPresentationFormSheet;
[self.navigationController presentViewController:documentPickerVC animated:YES completion:nil];

2.获取沙盒路径
// 获得文件沙盒地址

• (NSString *)getNativeFilePath:(NSString *)fileName {
  NSString *path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
  NSString *munu = [NSString stringWithFormat:@"%@/%@",@"downLoad",fileName];
  NSString *filePath = [path stringByAppendingPathComponent:munu];
  // 判断是否存在,不存在则创建
  NSFileManager *fileManager = [NSFileManager defaultManager];
  // fileExistsAtPath 判断一个文件或目录是否有效，isDirectory判断是否一个目录
  BOOL isDir = NO;
  NSMutableArray *theArr = [[filePath componentsSeparatedByString:@"/"] mutableCopy];
  [theArr removeLastObject];
  NSString *thePath = [theArr componentsJoinedByString:@"/"];
  BOOL existed = [fileManager fileExistsAtPath:thePath isDirectory:&isDir];
  if ( !(isDir == YES && existed == YES) ) { // 如果文件夹不存在
  [fileManager createDirectoryAtPath:thePath withIntermediateDirectories:YES attributes:nil error:nil];
  }
  return filePath;
  }

3.文件写入制定的路径
BOOL downResult = [fileData writeToFile:fullPath atomically:YES];

4. UIDocumentPickerDelegate的代理方法

pragma mark - UIDocumentPickerDelegate

• (void)documentPicker:(UIDocumentPickerViewController *)controller didPickDocumentsAtURLs:(NSArray<NSURL *> *)urls {
  // 获取授权
  BOOL fileUrlAuthozied = [urls.firstObject startAccessingSecurityScopedResource];
  if (fileUrlAuthozied) {
  // 通过文件协调工具来得到新的文件地址，以此得到文件保护功能
  NSFileCoordinator *fileCoordinator = [[NSFileCoordinator alloc] init];
  NSError *error;

    [fileCoordinator coordinateReadingItemAtURL:urls.firstObject options:0 error:&error byAccessor:^(NSURL *newURL) {
        // 读取文件
        NSString *fileName = [newURL lastPathComponent];
        NSError *error = nil;
        NSData *fileData = [NSData dataWithContentsOfURL:newURL options:NSDataReadingMappedIfSafe error:&error];
        if (error) {
            // 读取出错
        } else {
           
         
           
            // [self uploadingWithFileData:fileData fileName:fileName fileURL:newURL];
        }
  

// [self dismissViewControllerAnimated:YES completion:NULL];
}];
[urls.firstObject stopAccessingSecurityScopedResource];
} else {
// 授权失败
}
}