Toolbar：本质，Android 应用中的工具栏

<!-- 带有 Toolbar 的 activity_main.xml -->
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <androidx.appcompat.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        android:elevation="4dp"
        app:titleTextColor="@android:color/white"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

    <FrameLayout
        android:id="@+id/content_frame"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val toolbar = findViewById<Toolbar>(R.id.toolbar)
        setSupportActionBar(toolbar)

        // 设置导航图标
        supportActionBar?.setDisplayHomeAsUpEnabled(true)
        supportActionBar?.setHomeAsUpIndicator(R.drawable.ic_menu)

        // 自定义标题
        supportActionBar?.title = "主页"
        supportActionBar?.subtitle = "你好，用户！"
    }

    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        menuInflater.inflate(R.menu.toolbar_menu, menu)
        return true
    }
}

<!-- res/menu/toolbar_menu.xml -->
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <item
        android:id="@+id/action_search"
        android:icon="@drawable/ic_search"
        android:title="搜索"
        app:showAsAction="ifRoom"
        app:actionViewClass="androidx.appcompat.widget.SearchView" />

    <item
        android:id="@+id/action_notifications"
        android:icon="@drawable/ic_notifications"
        android:title="通知"
        app:showAsAction="ifRoom" />

    <item
        android:id="@+id/action_settings"
        android:title="设置"
        app:showAsAction="never" />
</menu>

override fun onOptionsItemSelected(item: MenuItem): Boolean {
    return when (item.itemId) {
        R.id.action_search -> {
            Toast.makeText(this, "搜索", Toast.LENGTH_SHORT).show()
            true
        }
        R.id.action_notifications -> {
            openNotifications()
            true
        }
        R.id.action_settings -> {
            openSettings()
            true
        }
        else -> super.onOptionsItemSelected(item)
    }
}

<!-- Material 3 Large Top App Bar 与 CollapsingToolbarLayout -->
<CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.material.appbar.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <com.google.android.material.appbar.CollapsingToolbarLayout
            android:layout_width="match_parent"
            android:layout_height="168dp"
            app:contentScrim="?attr/colorPrimary"
            app:titleEnabled="true"
            app:layout_scrollFlags="scroll|exitUntilCollapsed">

            <androidx.appcompat.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_collapseMode="pin" />
        </CollapsingToolbarLayout>
    </AppBarLayout>

    <androidx.core.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="16dp"
            android:text="屏幕内容..." />
    </NestedScrollView>
</CoordinatorLayout>

// Toolbar 高级定制
with (toolbar) {
    // 徽标和标题
    setLogo(R.drawable.ic_logo)
    setTitle("我的应用")
    setSubtitle("版本 2.0")

    // 带处理器的导航图标
    setNavigationIcon(R.drawable.ic_drawer)
    setNavigationOnClickListener {
        drawerLayout.open()
    }

    // 自定义视图——主题开关
    val themeSwitch = Switch(this@MainActivity).apply {\n        thumbDrawable = ContextCompat.getDrawable(
            this@MainActivity, R.drawable.ic_theme
        )
    }
    addView(themeSwitch)

    // 自定义 PopupMenu
    setOnMenuItemClickListener { item ->
        Toast.makeText(this@MainActivity, item.title, Toast.LENGTH_SHORT).show()
        true
    }
}