Android 解决toolbar标题不显示问题

<?xml version="1.0" encoding="utf-8"?>
<menu 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"
    tools:context=".MainActivity">
    <item
        android:id="@+id/advertise"
        android:checkable="true"
        android:icon="@mipmap/icon_connected"
        android:orderInCategory="100"
        android:title="ad"
        android:visible="true"
        android:showAsAction="ifRoom"
        app:showAsAction="ifRoom" />
    <item
        android:id="@+id/add_friends"
        android:checkable="true"
        android:icon="@mipmap/ic_launcher"
        android:orderInCategory="100"
        android:title="add friends"
        android:visible="true"
        android:showAsAction="ifRoom"
        app:showAsAction="ifRoom" />
</menu>

setSupportActionBar(toolbar);