每次显示 Android NavigationView 时如何以编程方式禁用和启用项目

Question

I am moving some menu items from the options menu to the navigation menu. My app uses a NavigationView that is populated by a menu as described at https://developer.android.com/reference/android/support/design/widget/NavigationView.html

One of the items calls webView.goBack() on the WebView in the main activity. When it was placed in the options menu, it was only enabled if webView.canGoBack() . Otherwise, it was disabled (grayed out). To accomplish this, onPrepareOptionsMenu() included the command:

back.setEnabled(webView.canGoBack());

As onPrepareOptionsMenu() is called every time the options menu is about to be displayed, this would update the status of the menu item to correctly reflect the state of the WebView .

However, I have not been able to replicate this behavior with the NavigationView. Is there a method or class similar to onPrepareOptionsMenu() that is called each time the NavigationView is prepared?

PS. Other people who have addressed similar questions have always referred to using a ListView, which was an older method of populating a navigation drawer. This question specifically relates to using a NavigationView with a menu.

Answer 1

The answer to this question is to add a DrawerListener and override onDrawerStateChanged .

// Create the navigation drawer.
drawerLayout = (DrawerLayout) findViewById(R.id.drawerLayout);
// The `DrawerTitle` identifies the drawer in accessibility mode.
drawerLayout.setDrawerTitle(GravityCompat.START, getString(R.string.navigation_drawer));

// Listen for touches on the navigation menu.
final NavigationView navigationView = (NavigationView) findViewById(R.id.navigationView);
navigationView.setNavigationItemSelectedListener(this);

// Get handles for `navigationMenu` and the back and forward menu items.  The menu is zero-based, so item 1 and 2 and the second and third items in the menu.
final Menu navigationMenu = navigationView.getMenu();
final MenuItem navigationBackMenuItem = navigationMenu.getItem(1);
final MenuItem navigationForwardMenuItem = navigationMenu.getItem(2);

// The `DrawerListener` allows us to update the Navigation Menu.
drawerLayout.addDrawerListener(new DrawerLayout.DrawerListener() {
    @Override
    public void onDrawerSlide(View drawerView, float slideOffset) {
    }

    @Override
    public void onDrawerOpened(View drawerView) {
    }

    @Override
    public void onDrawerClosed(View drawerView) {
    }

    @Override
    public void onDrawerStateChanged(int newState) {
        // Update the back and forward menu items every time the drawer opens.
        navigationBackMenuItem.setEnabled(webView.canGoBack());
        navigationForwardMenuItem.setEnabled(webView.canGoForward());
    }
});

Answer 2

NavigationView exposes its underlying Menu with getMenu() . You can use that to find menu items and make changes to them.