HarmonyOS 手写板保存报错

let path : string = this.context.cacheDir;
let fileName : string = new Date().getTime() + ".jpg";
this.initPath = path + "/" + fileName;
this.controller.onLoad(this.callback)


this.controller.save( this.initPath )
  .then(()=>{
  });

执行保存时报错：PencilEngineJs-HiSysEvent , error code: 202, error msg: Permission denied. System api can be invoked only by system applications.

手写完成后，如何获取手写图片？是否需要进行操作后才能获取，目前无法读取图片