React Navigation 2: How to check previous scene and to disable tab change

Question

I have a tab navigation. One of my tabs has a form and I would like to disable navigate event if my form data is not saved.

In ver.1, the tabBarOnPress method provides previousScene, scene and jumpToIndex, so I was able to check which scene I am leaving and to access its props.

Now in ver.2, the tabBarOnPress method provides the navigation props for the scene, but the previous scene prop is missing :/

navigationOptions: {
    tabBarOnPress: ({ navigation, defaultHandler }) => {
        // Check the previous screen
        // If I am leaving the home screen and the user has unsaved data
        // disable tab navigation
        // else change to the pressed tab
    },
},

Also, I tried with the navigation event listeners but the NAVIGATE action is already dispatched:

props.navigation.addListener('willBlur', () => {
    // Disable tab switching;
}),

Simple snack: https://snack.expo.io/@hristoeftimov/handle-tab-changes-in-react-navigation-v2

Any solutions how to disable tab switching before leave a tab?

Answer 1

I have found a much simpler way, using the getStateForAction.

const defaultGetStateForAction = MainStack.router.getStateForAction;
MainStack.router.getStateForAction = (action, state) => {
    if (!state) {
        return defaultGetStateForAction(action, state);
    }

    if (
        action.type === NavigationActions.NAVIGATE
        && state.routes[state.index].key === 'HomeTab'
    ) {
        const tab = state.routes[state.index];
        const currentRoute = tab.routes[tab.index];
        const currentRouteParams = currentRoute.params;

        if (currentRouteParams && currentRouteParams.isNavigationDisabled) {
            return currentRouteParams.showConfirmationDialog(action);
        }
    }

    return defaultGetStateForAction(action, state);
}

Every time when I switch between the tabs it jumps into getStateForAction where I can access the leaving tab (from state) and the next screen (from action).

So, when my action is NAVIGATE and the leaving screen/route is HoneTab I can change/disable the default state for action and to trigger showConfirmationDialog() - This is a function that I can set as a route parameter to my HomeTab screen.