只有一個按鈕的情況

<resources>
    <string name="app_name">照片</string>
</resources>
styles.xml

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
 
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>


        <!-- Toolbar styles -->
        <item name="toolbarStyle">@style/Widget.AppCompat.Toolbar</item>
    </style>

</resources>

mainActivity.java

Toolbar myToolbar = (Toolbar) findViewById(R.id.my_toolbar);
setSupportActionBar(myToolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);

activity_main.xml

<?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"
    tools:context="com.homelink.testtoolbar7.MainActivity">

    <android.support.v7.widget.Toolbar
        style="style/toolbarStyle"
        android:id="@+id/my_toolbar"
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="?attr/colorPrimary"
        android:minHeight="?attr/actionBarSize">

        <ImageView
            android:id="@+id/bluetoothState"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/fm_detailitem_walk"
            android:contentDescription="content_description_bluetooth_status"
            android:padding="8dp"
            android:layout_marginRight="10dp"
            android:layout_gravity="right"/>
    </android.support.v7.widget.Toolbar>


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

android toolbar效果2