单次I/O任务开发指导 (Promise和async/await)

Promise和async/await提供异步并发能力，适用于单次I/O任务的场景开发，本文以使用异步进行单次文件写入为例来提供指导。

1. 实现单次I/O任务逻辑。

   import fs from '@ohos.file.fs';
   import { BusinessError } from '@ohos.base';
   import common from '@ohos.app.ability.common';
   
   async function write(data: string, file: fs.File): Promise<void> {
     fs.write(file.fd, data).then((writeLen: number) => {
       console.info('write data length is: ' + writeLen)
     }).catch((err: BusinessError) => {
       console.error(`Failed to write data. Code is ${err.code}, message is ${err.message}`);
     })
   }
   

2. 采用异步能力调用单次I/O任务。示例中的filePath的获取方式请参见获取应用文件路径。

   async function testFunc(): Promise<void>  {
     let context = getContext() as common.UIAbilityContext;
     let filePath: string = context.filesDir + "/test.txt"; // 应用文件路径
     let file: fs.File = await fs.open(filePath, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE);
     write('Hello World!', file).then(() => {
       console.info('Succeeded in writing data.');
       fs.close(file);
     }).catch((err: BusinessError) => {
       console.error(`Failed to write data. Code is ${err.code}, message is ${err.message}`);
       fs.close(file);
     })
   }
   testFunc();