fileio.open文件路径错误怎么回事啊？

1. import featureAbility from '@ohos.ability.featureAbility';
2. let context = featureAbility.getContext();
3. context.getFilesDir().then((data) => {
4. let pathDir = data;
5. })
6. let filePath = pathDir + "/test.txt";
7. fileio.open(filePath, 0o1, 0o0200).then(function(number){
8. console.info("open file succeed");
9. }).catch(function(err){
10. console.info("open file failed with error:"+ err);
11. });

按照示例 无法打开已经存在的文件，始终错误，请大侠指教！！！