Asymmetric RelativeLayout behavior in Android

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The following two layout files produce different results:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://ift.tt/nIICcg"
  android:orientation="vertical"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:gravity="center">
  <RelativeLayout
    android:layout_width="match_parent" 
    android:layout_height="wrap_content"
    android:gravity="center">
    <View
      android:id="@+id/box"
      android:background="#ff0000"
      android:layout_width="0dp"
      android:layout_height="30dp"
      android:layout_alignParentLeft="true"
      android:layout_toLeftOf="@+id/next_box" />
    <View
      android:id="@+id/next_box"
      android:background="#0000ff"
      android:layout_width="60dp"
      android:layout_alignParentRight="true"
      android:layout_height="30dp"
      />
  </RelativeLayout>
</LinearLayout>

Result:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://ift.tt/nIICcg"
  android:orientation="vertical"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:gravity="center">
  <RelativeLayout
    android:layout_width="match_parent" 
    android:layout_height="wrap_content"
    android:gravity="center">
    <View
      android:id="@+id/box"
      android:background="#ff0000"
      android:layout_width="0dp"
      android:layout_height="30dp"
      android:layout_alignParentLeft="true"
       />
    <View
      android:id="@+id/next_box"
      android:background="#0000ff"
      android:layout_width="60dp"
      android:layout_alignParentRight="true"
      android:layout_height="30dp"
      android:layout_toRightOf="@+id/box"
      />
  </RelativeLayout>
</LinearLayout>

Result:

Both layouts are trying to describe the same constraints. Namely, the red rectangle should touch the left edge of the parent, the blue rectangle should touch the right edge of the parent, and they should appear next to each other horizontally. The only difference is whether you specify the "next to" constraint on the red rectangle or the blue rectangle. I figured out the reason which has to do with the measure resolution order generated by forming a dependency graph of the constraints, but I only figured it out through reading RelativeLayout's source code, and I couldn't find any documentation / notes regarding this behavior. Since RelativeLayout must be a commonly used layout component, is there a more intuitive explanation for this behavior, or is there some part of documentation that I am missing?

asked 42 secs ago

dementrock

176

Asymmetric RelativeLayout behavior in Android