HarmonyOS filePreview预览txt提示预览失败

export let mContext = getContext(this); 
 
Index.ets 
import { mContext } from '../entryability/EntryAbility'; 
 
//写文件 
function WriteFile() { 
  let filePath = mContext.filesDir + "/test.txt"; 
  let file = fs.openSync(filePath, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE); 
  let str: string = "hello, world"; 
  let writeLen = fs.writeSync(file.fd, str); 
  console.info("write data to file succeed and size is:" + writeLen); 
  fs.closeSync(file); 
} 
 
//遍历文件 
function GetFile() { 
  console.info('getDirectory mContext.filesDir:' + mContext.filesDir); 
  let listFileOption: ListFileOptions = { 
    recursion: true, 
    listNum: 0, 
  }; 
  let filenames = fs.listFileSync(mContext.filesDir, listFileOption); 
  console.info("listFile succeed, filenames.length:" + filenames.length); 
  for (let i = 0; i < filenames.length; i++) { 
    console.info("filename: %s", filenames[i]); 
  } 
} 
 
Button('WriteFile', { stateEffect: true, type: ButtonType.Capsule }) 
  .width('80%') 
  .height(40) 
  .margin(10) 
  .onClick(() => { 
    WriteFile() 
  }) 
Button('GetDirectory', { stateEffect: true, type: ButtonType.Capsule }) 
  .width('80%') 
  .height(40) 
  .margin(10) 
  .onClick(() => { 
    GetFile() 
  })EntryAbility.ets 
export let mContext = getContext(this); 
 
Index.ets 
import { mContext } from '../entryability/EntryAbility'; 
 
//写文件 
function WriteFile() { 
  let filePath = mContext.filesDir + "/test.txt"; 
  let file = fs.openSync(filePath, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE); 
  let str: string = "hello, world"; 
  let writeLen = fs.writeSync(file.fd, str); 
  console.info("write data to file succeed and size is:" + writeLen); 
  fs.closeSync(file); 
} 
 
//遍历文件 
function GetFile() { 
  console.info('getDirectory mContext.filesDir:' + mContext.filesDir); 
  let listFileOption: ListFileOptions = { 
    recursion: true, 
    listNum: 0, 
  }; 
  let filenames = fs.listFileSync(mContext.filesDir, listFileOption); 
  console.info("listFile succeed, filenames.length:" + filenames.length); 
  for (let i = 0; i < filenames.length; i++) { 
    console.info("filename: %s", filenames[i]); 
  } 
} 
 
Button('WriteFile', { stateEffect: true, type: ButtonType.Capsule }) 
  .width('80%') 
  .height(40) 
  .margin(10) 
  .onClick(() => { 
    WriteFile() 
  }) 
Button('GetDirectory', { stateEffect: true, type: ButtonType.Capsule }) 
  .width('80%') 
  .height(40) 
  .margin(10) 
  .onClick(() => { 
    GetFile() 
  })    let uiContext: common.UIAbilityContext = getContext(this) as common.UIAbilityContext; 
let displayInfo: filePreview.DisplayInfo = { 
  x: 100, 
  y: 100, 
  width: 800, 
  height: 800 
}; 
let fileInfo: filePreview.PreviewInfo = { 
  uri: `file://${jsonObject['filePath'] as string}`, 
  mimeType: jsonObject['mimeType'] as string 
}; 
try { 
  await filePreview.openPreview(uiContext, fileInfo, displayInfo); 
} catch (err) { 
  console.error('[DownloadPlugin] openPreview failed, err = ' + err.message); 
}