Searchview not showing in Toolbar

This is very odd. I'm using build tools 25.0.1 and support lib 25.1.0. For me the accepted answer was not necessary, but the way the menu item was defined needs a small change. I need it like so:

<menu xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  xmlns:app="http://schemas.android.com/apk/res-auto">
<item
    android:id="@+id/search"
    android:title="@string/search_title"
    android:icon="@drawable/ic_search_24dp"
    app:showAsAction="always|collapseActionView"
    app:actionViewClass="android.widget.SearchView"/>

Where app:showAsAction is the key. Lint underlines this as red and tells me:

Should use android:showAsAction when using the appcompat library.

However if I have it set to android:showAsAction then the search view simply does not appear. Go figure.

i have this problem too, i've changed Toolbar height to absolute value instead of wrap_content and problem solved. i don't know why but i think this issue is related to CoordinatorLayout and height of toolbar, something breaks the SearchView height. if i use LinearLayout instead of CoordinatorLayout and AppBarLayout it works.

menu.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/action_search"
        android:icon="@drawable/ic_search_white_24dp"
        android:orderInCategory="100"
        android:title="@string/action_search"
        app:actionViewClass="android.support.v7.widget.SearchView"
        app:showAsAction="always|collapseActionView" />
</menu>

layout.xml

<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="@dimen/toolbar_height"
            android:paddingTop="@dimen/toolbar_top_padding"
            android:background="?attr/colorPrimary"
            app:title="@string/drawer_item_publisher_customization"
            app:layout_scrollFlags="scroll|enterAlways|snap"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

        <android.support.design.widget.TabLayout
            android:id="@+id/tabLayout"
            app:tabGravity="fill"
            style="@style/DefaultTabLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

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

    <android.support.v4.view.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />

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

toolbar_height value:

<dimen name="toolbar_height">75dp</dimen>

Before absolute height value (layout_height:"wrap_content"):

After absolute height value (layout_height:"75dp"):

if you are using theme: .NoActionBar set this in your onCreate()

setSupportActionBar(toolbar);