You could use actionLayout from the support library.
menu.xml
<?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">
<item
android:id="@+id/button_item"
android:title=""
app:actionLayout="@layout/button_layout"
app:showAsAction="always"
/>
</menu>
button_layout.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="match_parent"
android:orientation="horizontal">
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
/>
</RelativeLayout>
Activity.java
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu, menu);
MenuItem item = menu.findItem(R.id.button_item);
Button btn = item.getActionView().findViewById(R.id.button);
btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Toast.makeText(MainActivity.this, "Toolbar Button Clicked!", Toast.LENGTH_SHORT).show();
}
});
return true;
}