Set height of Toolbar half of attr/actionBarSize in xml

Question

Is there anyway to set height of a "android.support.v7.widget.Toolbar" half of a predefined attr like "?android:attr/actionBarSize" in layout xml file? in fact I want the height of my toolbar be something like :

<android.support.v7.widget.Toolbar
    android:layout_width="match_parent"
    android:layout_height=("?android:attr/actionBarSize")/2
    >

Answer 1

It is not possible to perform arithmetic actions in xml.

If you want to give the value through xml, then you have to perform following:

1. in values/dimes.xml define a variable halfActionBar and make it be 28dp (original is 56dp).
2. in values-land/dimes.xml define a variable halfActionBar and make it be 24dp (original is 48dp).
3. in values-sw600dp-v13/dimes.xml define a variable halfActionBar and make it be 32dp (original is 64dp).

In your styles.xml theme.

<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="android:actionBarSize">@dimen/halfActionBar</item>
    ...
</style>

Then in your layout:

<android.support.v7.widget.Toolbar
    android:layout_width="match_parent"
    android:layout_height="?android:attr/actionBarSize"/>

Note, that this is a bad solution, because it depends on platform implementation. I advice to get actionBarSize from java/kotlin code (not from xml).

Answer 2

You can't do it in XML but if you want to go with the programmatically way you can try with something like this, i took the idea from here

//themedContext is an Activity or a Context which has a Theme attached,
//you can't use Application context for this
final TypedArray array = themedContext.getTheme().obtainStyledAttributes(
                new int[] { android.R.attr.actionBarSize });
int actionBarSize = (int) array.getDimensionPixelSize(0, -1);
array.recycle();

Then to apply this to the Toolbar you could do:

Toolbar myToolbar = (Toolbar) findViewById(R.id.my_toolbar);

RelativeLayout.LayoutParams layoutParams = 
                 (RelativeLayout.LayoutParams) myToolbar.getLayoutParams();
//half the height of toolbar prior to set its value
layoutParams.height = (int)(actionBarSize / 2);
myToolbar.setLayoutParams(layoutParams);

setSupportActionBar(myToolbar);

PS: don't forget that this attribute value changes when the device is rotated, so you should set this custom value every time the device changes from portrait to landscape and viceversa.