Bdtjtk

The boilerplate that Android Studio generates creates a style that extends Theme.AppCompat.Light.DarkActionBar. Somehow, this adds an actionbar/toolbar at the top of all my activities.

How does this happen? Where is the bar defined? It's nowhere in the layouts.

Android studio inflates custom Views or ViewGroups they have already defined, most of these you cannot see because they are private classes.

Here is an example of how you would do this in code.

class Test extends android.support.v7.widget.AppCompatTextView {





    public Test(Context context) {

        super(context);

        initTestView(null);

    }



    public Test(Context context, @Nullable AttributeSet attrs) {

        super(context, attrs);

        initTestView(attrs);

    }



    public Test(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {

        super(context, attrs, defStyleAttr);

        initTestView(attrs);

    }



    public void initTestView(AttributeSet as) {

        if (as != null) {

            TypedArray ta = getContext().obtainStyledAttributes(as, R.styleable.Test);



            String textOverride = ta.getString(R.styleable.Test_override);

            ta.recycle();



            setText("Test: " + textOverride);

        }

    }



}

Then you would define a styleable in the app/src/main/res/values/attr.xml

<declare-styleable name="Test">

    <attr name="override" format="string" />

</declare-styleable>

Now when Android inflates this, it can see your custom class as well as attributes to construct it with. If you were to add this to a layout it would automatically generate an example view of my code. This is the same as Androids core styled Views/ViewGroups and they will oftentimes have default values or visible representations of these class as they are inflated and attached to their parent views.

To make it perfectly clear, when you add an Android View into your layout, let's say for simplicity .

<TextView

  android:id="@+id/hello"

  android:text="@string/greeting"/>

The class for TextView is doing similar stuff to my examples initTestView method, by grabbing its typed properties (text, id) and populating the Views or values it has internally. It is, at its core, how Android glues xml values to their class representations.

With the help of Chris Sullivan we figured out what was going on. This is an estimated guess.

It turns out that using the Theme.AppCompat.Light.DarkActionBar style/theme just adds some type top margin to all activities and fills them with the primary color. This makes it look in the Android editor as if there's an app bar/toolbar/action bar, but it's just smoke and mirrors.

The actual app bar is added at runtime by AppCompatActivity.

This is defined in the styles xml. Your apptheme extends from it. If you want it to be gone you can extend another style for example Theme.AppCompat.Light.NoActionBar