在浮动操作按钮内导航

Question

我添加了主要活动。 我有一个 FAB 按钮，我试图通过单击按钮导航到其中一个片段。 但是我收到java.lang.IllegalArgumentException: navigation destination XXXXX/galleryFragment is unknown to this NavController不确定异常的原因是什么。 我是安卓开发新手，请原谅我的无知

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    DrawerLayout drawer = findViewById(R.id.drawer_layout);
    NavigationView navigationView = findViewById(R.id.nav_view);
    // Passing each menu ID as a set of Ids because each
    // menu should be considered as top level destinations.
    mAppBarConfiguration = new AppBarConfiguration.Builder(
            R.id.nav_home, R.id.nav_gallery, R.id.nav_slideshow)
            .setDrawerLayout(drawer)
            .build();
    NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
    NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
    NavigationUI.setupWithNavController(navigationView, navController);

    FloatingActionButton fab = findViewById(R.id.fab);
    Navigation.setViewNavController(fab, navController);

    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Navigation.findNavController(view).navigate(R.id.galleryFragment);
        }
    });
}

Answer 1

Navigation.findNavController(view)仅在视图位于NavHostFragment内NavHostFragment （即，它是由您的片段之一创建的视图）。

如果您的FloatingActionButton位于NavHostFragment之外（例如在您的活动布局中），那么您需要使用您在onCreate()使用的相同内容： Navigation.findNavController(this, R.id.nav_host_fragment) ：

fab.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        Navigation.findNavController(this, R.id.nav_host_fragment).navigate(R.id.galleryFragment);
    }
});

Answer 2

您可以将navController存储为全局变量，然后不要使用Navigation.findNavController ，使用navController.navigate 。

NavController navController = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
    ...
    navController = Navigation.findNavController(this, R.id.nav_host_fragment);
    NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
    NavigationUI.setupWithNavController(navigationView, navController);

    FloatingActionButton fab = findViewById(R.id.fab);

    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            navController.navigate(R.id.galleryFragment);
        }
    });
}