HarmonyOS 使用filePreview打开文件问题

let uiContext = getContext(this);
let displayInfo: filePreview.DisplayInfo = {
  x: 100,
  y: 100,
  width: 800,
  height: 800
};
let fileInfo: filePreview.PreviewInfo = {
  title: '1.txt',
  uri: 'file://docs/storage/Users/currentUser/Documents/2.pdf',
  mimeType: 'application/pdf'
};
filePreview.openPreview(uiContext, fileInfo, displayInfo).then(() => {
  console.info('Succeeded in openPreview');
}).catch((err: BusinessError) => {
  console.error(`Failed to openPreview, err.code = ${err.code}, err.message = ${err.message}`);
});

如上代码，使用filePreview来预览代码项目rawfile目录中的2.pdf文件，其中fileInfo中的uri怎么填写？