我不知道appcompat库中是否有任何变化，但这是相当微不足道的，不需要反射。

Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

// loop through all toolbar children right after setting support 
// action bar because the text view has no id assigned

// also make sure that the activity has some title here
// because calling setText() with an empty string actually
// removes the text view from the toolbar

TextView toolbarTitle = null;
for (int i = 0; i < toolbar.getChildCount(); ++i) {
    View child = toolbar.getChildAt(i);

    // assuming that the title is the first instance of TextView
    // you can also check if the title string matches
    if (child instanceof TextView) {
        toolbarTitle = (TextView)child;
        break;
    }
}

要在你的工具栏中使用自定义标题，你需要做的是记住，工具栏只是一个花哨的ViewGroup，所以你可以添加一个自定义标题，如下所示:

<android.support.v7.widget.Toolbar
    android:id="@+id/toolbar_top"
    android:layout_height="wrap_content"
    android:layout_width="match_parent"
    android:minHeight="?android:attr/actionBarSize"
    android:background="@color/action_bar_bkgnd"
    app:theme="@style/ToolBarTheme" >


     <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Toolbar Title"
        android:layout_gravity="center"
        android:id="@+id/toolbar_title" />


    </android.support.v7.widget.Toolbar>

这意味着你可以样式的TextView，但你想，因为它只是一个常规的TextView。在你的activity中，你可以像这样访问标题:

Toolbar toolbarTop = (Toolbar) findViewById(R.id.toolbar_top);
TextView mTitle = (TextView) toolbarTop.findViewById(R.id.toolbar_title);

这只是为了帮助使用@MrEngineer13回答@Jonik和@Rick Sanchez评论以正确的顺序加入所有作品，以帮助轻松实现标题居中!!

TextAppearance.AppCompat.Widget.ActionBar.Title的布局:

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:popupTheme="@style/AppTheme.PopupOverlay">

        <TextView
            android:id="@+id/toolbar_title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"                      
            style="@style/TextAppearance.AppCompat.Widget.ActionBar.Title"
            android:layout_gravity="center" />

    </android.support.v7.widget.Toolbar>

以正确的顺序实现方法:

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    TextView mTitle = (TextView) toolbar.findViewById(R.id.toolbar_title);

    setSupportActionBar(toolbar);
    mTitle.setText(toolbar.getTitle());

    getSupportActionBar().setDisplayShowTitleEnabled(false);

请不要忘记给@MrEngineer13的答案投票!!

下面是一个示例项目ToolbarCenterTitleSample

希望能帮助到别人;)

我不知道appcompat库中是否有任何变化，但这是相当微不足道的，不需要反射。

Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

// loop through all toolbar children right after setting support 
// action bar because the text view has no id assigned

// also make sure that the activity has some title here
// because calling setText() with an empty string actually
// removes the text view from the toolbar

TextView toolbarTitle = null;
for (int i = 0; i < toolbar.getChildCount(); ++i) {
    View child = toolbar.getChildAt(i);

    // assuming that the title is the first instance of TextView
    // you can also check if the title string matches
    if (child instanceof TextView) {
        toolbarTitle = (TextView)child;
        break;
    }
}

  @Composable
    fun topAppBar() {
        CenterAlignedTopAppBar(
            title = {
                Text(
                    "Top App Bar"
                )
            },
            navigationIcon = {
                IconButton(onClick = { /*TODO*/ }) {
                    Icon(
                        imageVector = Icons.Default.ArrowBack,
                        contentDescription = "Back"
                    )
                }
            },
            actions = {
                IconButton(onClick = { /*TODO*/ }) {
                    Icon(
                        imageVector = Icons.Default.MoreVert,
                        contentDescription = "More",
                    )
                }
            },
            colors = TopAppBarDefaults.smallTopAppBarColors(
                containerColor = MaterialTheme.colorScheme.secondaryContainer
            )
        )
    }
}

Material Components 1.4.0-alpha02中的MaterialToolbar现在能够通过设置titleCentered属性为true来居中工具栏的标题:

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

    <com.google.android.material.appbar.MaterialToolbar
        android:id="@+id/topAppBar"
        style="@style/Widget.MaterialComponents.Toolbar.Primary"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        app:titleCentered="true" />

</com.google.android.material.appbar.AppBarLayout>