<merge/> in custom View xml layout

Question

I have the following custom view which is based on RelativeLayout:

public class LearningModeRadioButton extends
                                        RelativeLayout
                                     implements
                                        Checkable,
                                        View.OnClickListener {

    private void init(Context context, AttributeSet attrs) {
        LayoutInflater.from(context).inflate(R.layout.rb_learning_mode, this, true);
    }
}

R.layout.rb_learning_mode contents are:

<?xml version="1.0" encoding="utf-8"?>

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

    <RadioButton
            android:id="@+id/rb"
            android:button="@drawable/sel_rb_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            />

    <TextView
            android:id="@+id/tv_mode_title"
            style="@style/text_regular"
            android:layout_toRightOf="@+id/rb"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            />

    <TextView
            android:id="@+id/tv_description"
            style="@style/text_small"
            android:layout_below="@+id/tv_mode_title"
            android:layout_alignLeft="@+id/tv_mode_title"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            />

</merge>

It sort of works, but layout parameters (layout_xxx) are ignored. I could use another <RelativeLayout/> as root element of the layout but I want to avoid having extra level in view hierarchy.

So the question is: How do I make layout attributes inside <merge/> work?

Answer 1

For anyone that might still be struggling with this, you should specify the parentTag attribute inside the merge tag. You will also need to specify layout_height and layout_width to make it work.

    <merge
        tools:parentTag="android.widget.RelativeLayout"
        tools:layout_width="match_parent"
        tools:layout_height="match_parent"
    >
    // Child Views
    </merge>

The editor should display everything properly now.

Answer 2

Merge useful for LinearLayout and FrameLayout its not suitable for RelativeLayout.

Obviously, using works in this case because the parent of an activity's content view is always a FrameLayout. You could not apply this trick if your layout was using a LinearLayout as its root tag for instance. The can be useful in other situations though.

check this: