如何自动缩放Android工具栏菜单图标？

Question

In my Android activity I've attempted to add a menu icon to a toolbar thus:

toolbar.inflateMenu(R.menu.toolbar_menu)

The menu is defined using an Android vector drawable:

<menu xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/toolbar_menu"
        android:icon="@drawable/menu"
        android:title="Menu"
        app:showAsAction="always"
        />

</menu>

The drawable:

<!-- drawable/menu.xml -->
<vector xmlns:android="http://schemas.android.com/apk/res/android"
    android:height="24dp"
    android:width="24dp"
    android:viewportWidth="24"
    android:viewportHeight="24">
    <path android:fillColor="#000" android:pathData="M3,6H21V8H3V6M3,11H21V13H3V11M3,16H21V18H3V16Z" />
</vector>

But in the emulator (Nexus 5X on the left, Nexus 10 on the right) the menu icon doesn't autoscale as I would expect:

This occurs under API 21 and API 26.

I thought using vector drawables was supposed to lead to auto-scaled images, but it's clearly not occurring here. How can I get this menu to scale properly without resorting to per-resolution raster images?

Answer 1

Try adding android:scaleType="fitXY" ?

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