What is the ButtonBarLayout and how should we use it?

Question

When I developed, I found a new widget called android.support.v7.widget.ButtonBarLayout unexpectedly. I tried to search it on the internet, but nothing was found, e

Answer 1

You are right first of all. ButtonBar layout does not seem to be featured anywhere in the official Android documentation. I tried myself to search about it, but to no avail. However I have found some information which defines what is a ButtonBar layout and when to use it. Hopefully this will help you.

Most tutorials use the Buttonbar layout in a dialogbox or at the bottom of a screen to confirm or decline an option. The image below is a visual representation of how the ButtonBar layout has been used in a screen.

The screenshot above has the following layout xml:

<LinearLayout
    style="?android:attr/buttonBarStyle"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal" >

    <Button
        android:id="@+id/Button01"
        style="?android:attr/buttonBarButtonStyle"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="Show" />

    <Button
        android:id="@+id/Button02"
        style="?android:attr/buttonBarButtonStyle"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="Change" />
</LinearLayout>

<EditText
    android:id="@+id/myView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ems="10" >

    <requestFocus />
</EditText>

So essentially what Android is doing here is simply creating two buttons next to each other in a LinearLayout with each button having the match_parent parameter set to the width. Hence each button takes half the size of the screen. Android have actually taken away the hassle of creating seperate buttons and positioning them correctly to fit different screens, by creating a simple widget handling this altogether.

As with the support library, Android have implemented this for developers using an earlier API. It is normal for them to use the support library for this purpose.

Hope this helps :)