Ionic-native-file can't read file at first time after save file Ask Question

I can’t read file at first time after saving file.
-But when i restart the app i can read file.
-And I set “Application supports iTunes file sharing”, i can read file at first time.

//File save

 this.file.writeFile(filedir,'sample.txt','hellow owlrd')
        .then((data)=>{
            this.viewCtrl.dismiss();
        }).catch(err=>
        {
            alert('ff'+JSON.stringify(err));
        });

//File Read

 this.file.writeFile(filedir + 'recordtext' ,'sample'+numstr+'.txt',this.content)
        .then((data)=>{
            this.viewCtrl.dismiss();
        }).catch(err=>
        {
            alert('ff'+JSON.stringify(err));
        });

It seems that close file not work well.
I don’t know the reason correctly.
Please help.