Android MainActivity 代码示例: 使用 FloatingActionButton 和 权限检查

public class MainActivity extends AppCompatActivity {

private static final int PERMISSION_REQUEST_CODE = 123;
private AppBarConfiguration mAppBarConfiguration;
private ActivityMainBinding binding;
private FloatingActionButton fab;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    binding = ActivityMainBinding.inflate(getLayoutInflater());
    setContentView(binding.getRoot());

    setSupportActionBar(binding.appBarMain.toolbar);
    fab = binding.appBarMain.fab;
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, '不知加什么.ing', Snackbar.LENGTH_LONG)
                    .setAction('Action', null).show();
        }
    });

    DrawerLayout drawer = binding.drawerLayout;
    NavigationView navigationView = binding.navView;

    // 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)
            .setOpenableLayout(drawer)
            .build();

    NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment_content_main);
    NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
    NavigationUI.setupWithNavController(navigationView, navController);

    // Check storage permission
    if (!checkStoragePermission()) {
        requestStoragePermission();
    }
}

// Check if storage permission is granted
private boolean checkStoragePermission() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
        int result = ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE);
        return result == PackageManager.PERMISSION_GRANTED;
    } else {
        return true;
    }
}

}

<com.google.android.material.floatingactionbutton.FloatingActionButton android:id="@+id/fab" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="bottom|end" android:layout_margin="16dp" app:srcCompat="@android:drawable/ic_dialog_email" />