Android Lollipop, add popup menu from title in toolbar

I'm unable to see how adding a popup menu from the title is accomplished like is shown in many of the material design examples. Any help would be much appreciated.

You're going to need to add a Spinner to the Toolbar:

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

    <Spinner
            android:id="@+id/spinner_nav"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

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

You will then need to disable the default title:

Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayShowTitleEnabled(false);

You can then retrieve and setup the Spinner as needed in your Activity/Fragment.

I came across this question while I was trying to find a solution to prevent the popup to overlay the spinner and I would like to leave here an alternative solution to this question as its possible to add the spinner to the toolbar using the menu.xml as well

activity_main.xml

<LinearLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:fitsSystemWindows="true">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorAccent" />

</android.support.design.widget.AppBarLayout>

 <!-- Other layout widgets -->

</LinearLayout>

menu_main.xml

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

<item
    android:id="@+id/spinner"
    android:title="Spinning"
    app:actionViewClass="android.widget.Spinner"
    app:showAsAction="always" />

<!-- Other items -->

</menu>

Your Activity

It will be necessary to override the onCreateOptionMenu() method, then use getMenuInflater() to inflate the menu file created earlier.

You will also need to get the Spinner item and set an adapter to it as you would normally do.

   @Override
public boolean onCreateOptionsMenu(Menu menu) {

    getMenuInflater().inflate(R.menu.menu_main, menu);

    //Get Spinner item from menu

    MenuItem spinnerMenuItem = menu.findItem(R.id.spinner);
    final Spinner spinner = (Spinner) MenuItemCompat.getActionView(spinnerMenuItem);

    //Set adapter whichever way you prefer (from the resource or manually)

    final ArrayAdapter<CharSequence> spinnerAdapter = ArrayAdapter
            .createFromResource(this, R.array.items_array, android.R.layout.simple_spinner_dropdown_item);
    spinnerAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinner.setAdapter(spinnerAdapter);

    return true;

}

Style.xml

Finally, if you want to customize your spinner

<resources>

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="android:spinnerStyle">@style/spinner_style</item>
</style>

<style name="spinner_style" parent="Widget.AppCompat.Spinner">
    <item name="android:dropDownVerticalOffset">40dip</item>
    <!--<item name="android:dropDownHorizontalOffset">0dip</item>-->
    <item name="overlapAnchor">false</item>

    <!--Other customizations-->

</style>