Android抽屉布局可能产生空指针异常

Question

我不断在我的代码中收到此警告，我开始担心，因为我接近完成的最后期限。我在主 activity 中有一个 DrawerLayout，使用 Android Studio 自己的导航抽屉 activity，但由于 DrawerLayout setDrawerListener 现在已弃用，因此不得不对代码进行轻微更改。

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //Firebase reference to main application URL and 'today's' matches
    Firebase mainRef = new Firebase(cons.getFirebaseUrl());

    //DrawerLayout settings for the navigation drawer
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.addDrawerListener(toggle);
    toggle.syncState();

    //Retrieve the navigation drawer and set it's listener for menu item presses
    navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);

我在 drawer.addDrawerListener(toggle) 和 navigationView.setNavigationItemSelectedListener(this)

收到警告

在我的代码中，我也通过这种方法接收它：

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) // This line gets the warning {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        super.onBackPressed();
    }
}

提前感谢任何可能知道是什么原因造成的人。我搜索了这个问题，但找不到关于 post 弃用方法的示例。

Answer 1

确保您在 support-v7-appcompat 中使用了 ActionBarDrawerToggle。

替换代码drawerLayout.setDrawerListener(actionBarDrawerToggle);

来自 drawerLayout.addDrawerListener(actionBarDrawerToggle);

最后，像这样检查空抽屉和空导航视图：

        DrawerLayout drawer = (DrawerLayout)findViewById(R.id.drawer_layout);

        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        assert drawer != null;
        drawer.addDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        assert navigationView != null;
        navigationView.setNavigationItemSelectedListener(this);

Android抽屉布局可能产生空指针异常

Android drawer layout may produce null pointer exception

android

android-navigation

navigation-drawer

android-drawer