Navigation Drawer切换Fragment求助：替换初始Google Map Fragment

嘿，你已经把导航抽屉和谷歌地图的基础框架搭好了，现在就差实现Fragment切换的逻辑啦，别担心，这几步就能搞定：

第一步：把固定的Map Fragment改成可替换的容器 #

你现在的content_nav.xml里直接写了静态的SupportMapFragment，没法动态替换，我们得换成FrameLayout作为Fragment的容器：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:app="http://schemas.android.com/apk/res-auto" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    app:layout_behavior="@string/appbar_scrolling_view_behavior" 
    tools:context=".NavActivity" 
    tools:showIn="@layout/app_bar_nav">

    <!-- 用FrameLayout作为Fragment的容器，替换原来的静态map fragment -->
    <FrameLayout
        android:id="@+id/fragment_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</android.support.constraint.ConstraintLayout>

第二步：在onCreate中初始加载Map Fragment #

现在xml里没有默认的Map Fragment了，我们要在onCreate里动态把它加载到容器中：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_nav);
    mAuth = FirebaseAuth.getInstance();
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    FloatingActionButton fab = findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });
    DrawerLayout drawer = 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();
    NavigationView navigationView = findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);
    navigationView.setCheckedItem(R.id.nav_home);
    /*Update the UI with user info*/
    FirebaseUser user = mAuth.getCurrentUser();
    TextView email = navigationView.getHeaderView(0).findViewById(R.id.navEmail);
    email.setText(user.getEmail());
    TextView name = navigationView.getHeaderView(0).findViewById(R.id.navUsername);
    name.setText(user.getDisplayName());

    // 初始加载Map Fragment到容器中，避免配置变化重复加载
    if (savedInstanceState == null) {
        SupportMapFragment mapFragment = new SupportMapFragment();
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.fragment_container, mapFragment)
                .commit();
        mapFragment.getMapAsync(this);
    }
}

第三步：完善onNavigationItemSelected的切换逻辑 #

现在你可以在每个菜单选项的分支里，创建对应的Fragment实例，然后替换容器里的内容。假设你已经有了ProfileFragment、SlideshowFragment这些自定义Fragment，代码可以这么写：

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    int id = item.getItemId();
    Fragment selectedFragment = null;

    if (id == R.id.nav_home) {
        // 回到地图Fragment
        selectedFragment = new SupportMapFragment();
        ((SupportMapFragment)selectedFragment).getMapAsync(this);
    } else if (id == R.id.nav_profile) {
        // 替换成个人资料Fragment
        selectedFragment = new ProfileFragment();
    } else if (id == R.id.nav_slideshow) {
        // 替换成幻灯片Fragment
        selectedFragment = new SlideshowFragment();
    } else if (id == R.id.nav_tools) {
        // 替换成工具Fragment
        selectedFragment = new ToolsFragment();
    } else if (id == R.id.nav_share) {
        // 处理分享逻辑，不需要Fragment的话直接提示即可
        Snackbar.make(findViewById(R.id.fragment_container), "分享功能待实现", Snackbar.LENGTH_SHORT).show();
    } else if (id == R.id.nav_logout) {
        mAuth.signOut();
        SharedPreferences sp = getSharedPreferences("Login", MODE_PRIVATE);
        SharedPreferences.Editor Ed = sp.edit();
        Ed.putString("Email", null);
        Ed.putString("Password", null);
        Ed.apply();
        Intent intent = new Intent(getApplicationContext(), MainActivity.class);
        startActivity(intent);
        finish(); // 退出当前页面，避免返回
    }

    // 如果有选中的Fragment，执行替换操作
    if (selectedFragment != null) {
        getSupportFragmentManager().beginTransaction()
                .replace(R.id.fragment_container, selectedFragment)
                .commit();
    }

    DrawerLayout drawer = findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}

一些小提示 #

• 记得提前创建好对应的自定义Fragment类（比如ProfileFragment），不然代码会报错哦。
• 如果想给Fragment切换加动画，可以在beginTransaction()之后加上setCustomAnimations()方法，比如setCustomAnimations(R.anim.fade_in, R.anim.fade_out)。
• 对于不需要Fragment的菜单选项，直接处理业务逻辑即可，不用赋值selectedFragment。

内容的提问来源于stack exchange，提问作者Denis