back_button_interceptor 4.0.1

Back Button Interceptor. May be used to intercept the Android back-button, as an alternative to `WillPopScope`.

back_button_interceptor

When you need to intercept the Android back-button, you usually add WillPopScope to your widget tree. However, under some use cases, specially when developing stateful widgets that interact with the back button, it may be more convenient to use the BackButtonInterceptor.

You may add functions to be called when the back button is tapped. These functions may perform some useful work, and then, if any of them return true, the default button process (usually popping a Route) will not be fired.

In more detail: All added functions are called, in order. If any function returns true, the combined result is true, and the default button process will NOT be fired. Only if all functions return false (or null), the combined result is false, and the default button process will be fired.

Optionally, you may provide a z-index. Functions with a valid z-index will be called before functions with a null z-index, and functions with larger z-index will be called first. When they have the same z-index, functions added last are called first.

Each function gets the boolean stopDefaultButtonEvent that indicates the current combined result from all the previous functions. So, if some function doesn't want to fire if some other previous function already fired, it can do:

if (stopDefaultButtonEvent) return false;

The same result may be obtained if the optional ifNotYetIntercepted parameter is true. Then the function will only be called if all previous functions returned false (that is, if stopDefaultButtonEvent is false).

Note: After you've finished you MUST remove each function by calling the remove() method.

Note: If any of your interceptors throws an error, a message will be printed to the console, but the error will not be thrown. You can change the treatment of errors by changing the static errorProcessing field.

Usage

Import the package

First, add back_button_interceptor as a dependency in your pubspec.yaml

Then, import it:

import 'package:back_button_interceptor/back_button_interceptor.dart';

Example usage

@override
void initState() {
   super.initState();
   BackButtonInterceptor.add(myInterceptor);
}

@override
void dispose() {
   BackButtonInterceptor.remove(myInterceptor);
   super.dispose();
}

bool myInterceptor(bool stopDefaultButtonEvent) {
   print("BACK BUTTON!"); // Do some stuff.
   return true;
}

Don't forget to check the example tab.

See also:

• https://docs.flutter.io/flutter/widgets/WillPopScope-class.html
• https://stackoverflow.com/questions/45916658/de-activate-system-back-button-in-flutter-app-toddler-navigation