Some Tips About Layout Resource

<?xml version="1.0" encoding="utf-8"?>
<ViewGroup
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@[+][package:]id/resource_name"
android:layout_height=["dimension" | "match_parent" | "wrap_content"]
android:layout_width=["dimension" | "match_parent" | "wrap_content"]
[ViewGroup-specific attributes] >
<View
android:id="@[+][package:]id/resource_name"
android:layout_height=["dimension" | "match_parent" | "wrap_content"]
android:layout_width=["dimension" | "match_parent" | "wrap_content"]
[View-specific attributes] >
<requestFocus/>
</View>
<ViewGroup >
<View />
</ViewGroup>
<include layout="@layout/layout_resource"/>
</ViewGroup>

<1>

<include>

Includes a layout file into this layout.
attributes:

layout

Layout resource. Required. Reference to a layout resource.

android:id

Resource ID. Overrides the ID given to the root view in the included layout.

android:layout_height

Dimension or keyword. Overrides the height given to the root view in the included layout. Only effective if

android:layout_width

is also declared.

android:layout_width

Dimension or keyword. Overrides the width given to the root view in the included layout. Only effective if

android:layout_height

is also declared.
You can include any other layout attributes in the

<include>

that are supported by the root element in the included layout and they will override
those defined in the root element.

Caution: If you want to override layout attributes using the

<include>

tag, you must override both

android:layout_height

and

android:layout_width

in
order for other layout attributes to take effect.
Another way to include a layout is to use

ViewStub

.
It is a lightweight View that consumes no layout space until you explicitly inflate it, at which point, it includes a layout file defined by its

android:layout

attribute. For more information about using

ViewStub

,
read Loading Views On Demand.
Note: One drawback of

ViewStub

is
that it doesn’t currently support the

<merge>

tag in the layouts to be inflated.

<2>
<requestFocus>

Any element representing a

View

object can include this empty element, which
gives its parent initial focus on the screen. You can have only one of these elements per file.<3>

<3>
<merge>

An alternative root element that is not drawn in the layout hierarchy. Using this as the root element is useful when you know that this layout will be placed into a layout that already contains the appropriate parent View
to contain the children of the

<merge>

element.
This is particularly useful when you plan to include this layout in another layout file using

<include>

and
this layout doesn't require a different

ViewGroup

container. For
more information about merging layouts, read Re-using Layouts with <include/>.

From:https://developer.android.com/guide/topics/resources/layout-resource.html

============================================================================================================

Define a ViewStub

ViewStub

is a lightweight view with no dimension that doesn’t draw anything or participate
in the layout. As such, it's cheap to inflate and cheap to leave in a view hierarchy. Each

ViewStub

simply
needs to include the

android:layout

attribute to specify the layout to inflate.

The following

ViewStub

is for a translucent progress bar overlay. It should be visible
only when new items are being imported into the application.

<ViewStub
android:id="@+id/stub_import"
android:inflatedId="@+id/panel_import"
android:layout="@layout/progress_overlay"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_gravity="bottom" />

Load the ViewStub Layout

When you want to load the layout specified by the

ViewStub

, either set it visible by calling

setVisibility(View.VISIBLE)

or
call

inflate()

.

findViewById(R.id.stub_import)).setVisibility(View.VISIBLE);
// or
View importPanel = ((ViewStub) findViewById(R.id.stub_import)).inflate();

Note: The

inflate()

method returns the inflated

View

once
complete. so you don't need to call

findViewById()

if you need to interact
with the layout.

Once visible/inflated, the

ViewStub

element
is no longer part of the view hierarchy. It is replaced by the inflated layout and the ID for the root view of that layout is the one specified by the

android:inflatedId

attribute of the ViewStub. (The ID

android:id

specified
for the

ViewStub

is valid only until the

ViewStub

layout
is visible/inflated.)

Note: One drawback of

ViewStub

is
that it doesn’t currently support the

<merge>

tag in the layouts to be inflated.

From: https://developer.android.com/training/improving-layouts/loading-ondemand.html