React native - prevent user from going back to login screen

Using Navigator, you can use resetTo(startingRoute) method to reset the stack and start a new one from the route you past as a parameter. Doing this you will prevent to navigate back in the stack.

If I'm not misunderstanding your component, you should use something like this:

goToCategoryView = () => {
    //Replace here push with resetTo
    this.props.navigator.resetTo({
        title: 'Categories',
        component: CategoryView,
    })
}

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