What is the difference between gravity and layout_gravity in Android?

 

In Android, both gravity and layout_gravity are attributes used to control the positioning and alignment of views within their parent layout, but they have different purposes and apply to different elements:

1. gravity:

   • gravity is an attribute that you apply to a child view (e.g., a TextView, Button, or ImageView) to control the alignment of the content within the view itself.
   • It defines how the content of the view should be aligned within the boundaries of the view.
   • The possible values for gravity include "left," "right," "top," "bottom," "center," "center_vertical," "center_horizontal," and various combinations of these.
   • gravity is used to position and align the content within the view and has no effect on the position of the view itself within its parent.

2. layout_gravity:

   • layout_gravity is an attribute that you apply to a child view within a ViewGroup (e.g., a LinearLayout, RelativeLayout, or FrameLayout) to control the positioning of the view within its parent.
   • It defines how the child view should be aligned or positioned within the boundaries of its parent layout.
   • The possible values for layout_gravity include "left," "right," "top," "bottom," "center," "center_vertical," "center_horizontal," and various combinations of these.
   • layout_gravity is used to position the view within its parent layout and has no effect on the alignment of the content within the view.

Here's an example to illustrate the difference between gravity and layout_gravity:

xml

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="This is a TextView with gravity"
        android:gravity="center"
        android:layout_gravity="center_horizontal"/>

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="This is a Button with layout_gravity"
        android:layout_gravity="center_horizontal"/>
</LinearLayout>

In this XML layout:

• The TextView uses the gravity attribute with the value "center" to align its content (the text) in the center horizontally within the boundaries of the view itself. It also uses layout_gravity to position the view in the center horizontally within its parent LinearLayout.

• The Button uses layout_gravity with the value "center_horizontal" to position itself in the center horizontally within its parent LinearLayout. It does not use the gravity attribute because it doesn't affect the positioning of the view itself.

As a result:

• The TextView's content is centered within the view, and the view is positioned in the center horizontally within its parent layout.

• The Button is positioned in the center horizontally within its parent layout, but the text within the button is not affected by the gravity attribute.

In summary, gravity controls the alignment of content within a view, while layout_gravity controls the positioning of a view within its parent layout. These attributes are used to achieve different layout and alignment effects in Android UI design.