fill_parent vs match_parent vs wrap_content

A new Android developer may get confused about what's the difference between fill_parent, match_parent, and wrap_content.

What are they ?

These three are called as Layout Parameters. They are used by sub-views to tell the parent view how they want to be laid on the Activity screen i.e we can set the Horizontal and Vertical size of a view using Layout Parameters.

To specify how big a view must be we use android:layout_width and android:layout_height attributes.

The values of these attributes can either one of fill_parent, match_parent or wrap_content.

1. match_parent

When you set layout width and height as match_parent, it will occupy the complete area that the parent view has, i.e. it will be as big as the parent.

Note: If a parent has applied to padding then that space would not be included.

When we create a layout.xml by default we have RelativeLayout as default parent View with android:layout_width="match_parent" and android:layout_height="match_parent" i.e it occupies the complete width and height of the mobile screen.

Also note that padding is applied to all sides,

android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"

Now lets add a sub-view LinearLayout and sets its layout_width="match_parent" and layout_height="match_parent", the graphical view would display something like this,

xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.code2care.android.togglebuttonexample.MainActivity" >

    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true"
    android:layout_marginLeft="11dp"
    android:background="#FFFFEE"
    android:orientation="vertical" >