Preview layout with merge root tag in Intellij IDEA/Android Studio

Question

Let's imagine we are developing compound component based on LinearLayout. So, we create class like this:

public class SomeView extends LinearLayout {
    public SomeView(Context context, AttributeSet attrs) {
        super(context, attrs);

        setOrientation(LinearLayout.VERTICAL);
        View.inflate(context, R.layout.somelayout, this);
    }
}

If we'll use LinearLayout as a root of somelayout.xml , we'll have extra view level, so we use merge tag:

<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Some text"
        android:textSize="20sp"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Some other text"/>
</merge>

But in Preview tab in IDE merge always acts as FrameLayout, and we'll see something like that:

(It is Android Studio, Intellij IDEA is just the same, about Eclipse I don't know)

Preview speed up developing layouts a lot, it's sad lose such a great help even for some layouts. May be there is a way to specify, how Preview should interpret merge tag in particular layout?

Answer 1

There is a new parentTag tools attribute ( added in Android Studio 2.2 ) that you can use to specify the layout type for a merge tag, which will make the layout render correctly in the layout editor preview.

So using your example:

<merge xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:parentTag="LinearLayout"
    tools:orientation="horizontal">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Some text"
        android:textSize="20sp"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Some other text"/>
</merge>

Note : Both android:layout_width and android:layout_height must be specified in order for the layout to display properly in the editor.

Answer 2

Edit: Outdated answer. See answer by starkej2.

---

Android Studio 0.5.8 added support for tools:showIn. By using it it is possible to preview < merge > layouts.

http://tools.android.com/recent/androidstudio058released

layout/layout_merge.xml with tools:showIn:

<merge xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:custom="http://schemas.android.com/apk/res-auto"
   xmlns:tools="http://schemas.android.com/tools"
   tools:showIn="@layout/simple_relativelayout">

......

</merge>

layout/simple_relativelayout.xml with include:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <include layout="@layout/layout_merge"/>

</RelativeLayout>

Answer 3

Is also possible use custom class as parent instead of merge like

<com.mycompany.SomeView xmlns:android="http://schemas.android.com/apk/res/android">
...
</com.mycompany.SomeView>

And then directly inflate this layout and cast result view to SomeView . Android studio will directly check parent class of SomeView and handle preview like LinerLayout . You can use onFinishInflate() method in the SomeView to bind views by findViewById() . Benefit of this solution is that you can put all layout definitions or style definition directly to the layout file, you can't use method like setOrientation() in code.