HarmonyOS 沙箱路径filesDir下无法使用open创建新文件

请参考示例如下：

// pages/xxx.ets
import { fileIo as fs, ReadOptions } from '@kit.CoreFileKit';
import { common } from '@kit.AbilityKit';
import { buffer } from '@kit.ArkTS';

// 获取应用文件路径
let context = getContext(this) as common.UIAbilityContext;
let filesDir = context.filesDir;

function createFile(): void {
  // 新建并打开文件
  let file = fs.openSync(filesDir + '/test.txt', fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE);
  // 写入一段内容至文件
  let writeLen = fs.writeSync(file.fd, "Try to write str.");
  console.info("The length of str is: " + writeLen);
  // 从文件读取一段内容
  let arrayBuffer = new ArrayBuffer(1024);
  let readOptions: ReadOptions = {
    offset: 0,
    length: arrayBuffer.byteLength
  };
  let readLen = fs.readSync(file.fd, arrayBuffer, readOptions);
  let buf = buffer.from(arrayBuffer, 0, readLen);
  console.info("the content of file: " + buf.toString());
  // 关闭文件
  fs.closeSync(file);
}

@Entry
@Component
struct Index {
  @State message: string = 'Hello World';
  build() {
    Column() {
      Text(this.message)
        .onClick(()=>{
          createFile();
        })
    }
    .height('100%')
    .width('100%')
  }
}