Why does LinearLayout not correctly display nested FrameLayout?

Question

I have an XML layout where I nested a FrameLayout within a LinearLayout and attempted to stack a sibling viewing group on top of the FrameLayout. It does not show the sibling viewing group at all, but just the FrameLayout. I wanted to please get some help in understanding why replacing the root ViewGroup to a RelativeLayout produces an expected output.

Here is the Layout:

<?xml version="1.0" encoding="utf-8"?>  
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:orientation="vertical">
     <FrameLayout  
         android:layout_width="match_parent"  
         android:layout_height="match_parent"
         android:id="@+id/mainFrameLayout"
         android:background="#787878"/>
    <LinearLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:orientation="vertical">  
         <ImageView  
             android:id="@+id/ImageView01"  
             android:layout_height="wrap_content"  
             android:layout_width="match_parent"  
             android:src="@drawable/download"  
             android:adjustViewBounds="true"/>
         <TextView  
             android:layout_width="match_parent"  
             android:layout_height="wrap_content"  
             android:textColor="#000"  
             android:textSize="40sp"  
             android:text="Top text" />
         <TextView
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             android:layout_gravity="bottom"
             android:gravity="right"
             android:text="bottom_text"
             android:textColor="#fff"
             android:textSize="50sp" />
</LinearLayout>

</LinearLayout>

I only see the FrameLayout by itself filling the screen. When I change the root ViewGroup to a RelativeLayout defined with a layout_height and layout_width to "match_parent", I get my expected output where the ImageView and both TextViews show on top of the FrameLayout. I am confused on how that made it work because I didn't specify any RelativeLayout parameters to the child ViewGroups/View like "bottomof" or "topof".

Is there a resizing propery or weight distribution that RelativeLayout has that LinearLayout does not? I have been looking online, but unfortunately have not found an answer.

Thank you!

Answer 1

In the code you showed, the first FrameLayout matches the parent's height, so the LinearLayout that follows is pushed offscreen below (y-axis, not z-axis) the FrameLayout. This is because their parent is a LinearLayout, which arranges it's children one below the other vertically (y-axis), non-overlaping (as in a roll of toiler paper where each view is a paper square).

If you wanted the child FrameLayout and LinearLayout to be on top of the other (z-axis) their parent would have to be a FrameLayout, which arranges it's children one on top of the other overlaping in the z-axis (as in a stack of paper sheets).

As to why a RelativeLayout without specifying layout parameters gave you your expected behavior, it's because the default is to place child views at the top left corner of the container (from RelativeLayout documentation):

By default, all child views are drawn at the top-left of the layout, so you must define the position of each view using the various layout properties available from RelativeLayout.LayoutParams.

Answer 2

You should remove match_parent from FrameLayout as Linearlayout in vertical orientation placed the view one after another.

In your case, FrameLayout is responsible for taking the entire device screen hence remaining views are getting pushed offscreen.