I'm trying to avoid the default behaviour of Flutter, instead of closing app when the back button (of the smartophone of course) is pressed I will send the app in background, so when I try to reopen the app it returns on the last screen. 

I also tried a solution that I have found here, but didn't work.
This is the code:

```
 return WillPopScope(
    onWillPop: () async =>
       await SystemChannels.platform.invokeMethod('SystemNavigator.pop'),
    child: Scaffold(

```

It also closes the app and don't send it in background.
The screen that contains the code showed above is the last route.