Ionic3 setRootNav issue

tutorials
1

(getRootNav) is deprecated and will be removed in the next major release. Use getRootNavById instead.
How can i use getRootById, I can’t fix my issues

2 
constructor(private appCtrl: App) {
  this.appCtrl.getRootById('n4');
}
3

Thanks for your answer.
But now i want to do like this
this.appCtrl.getRootById(‘n4’).setRoot(‘TabPage’).then(success=>{
loading.dismiss();
})

TabPage is Tabbar Controller
But this is not working. Show previous page info.
Please help me

4

What you mean Show previous page info?
this thing have to work

5

Thanks
I will explain structure of my app
1 . splash page -> TabbarPage(include 4 pages)
2. when click listitem of first page in Tabbar, I can see Other Tabbar, but first page of Other Tabbar is showing firstpage of First Tabbar
I don’t know what’s wrong,

6

this.appCtrl.getRootById(‘n4’).setRoot(‘TabPage’).then(success=>{

loading.dismiss();

})

In here, getRootById or getRootNavById?
Which is correct?