Gravity attributes defined in Android are
- android:gravity : Sets the gravity of the contents (i.e. its subviews) of the View it’s used on. Gravity arranges the content inside the view.
- android:layout_gravity : Sets the gravity of the View or Layout relative to its parent. It arranges a view in its layout.
So gravity arranges the content inside the view. layout_gravity arranges the view’s position outside of itself. Important points are
- layout_gravity does not work for views in a RelativeLayout. It is only supported for views in a LinearLayout or FrameLayout.
- View width and/or height has to be greater than its content. Otherwise gravity won’t have any effect. So wrap_content and gravity should not be used together.
- View width and/or height has to be less than the parent. Otherwise layout_gravity won’t have any effect. So match_parent and layout_gravity should not be used together.
Placing View
Commonly used constant used in android:gravity and android:layout_gravity for placing an object within a potentially larger container are given in below table.
| Constant | Description |
|---|---|
| center | Place the object in the center of its container in both the vertical and horizontal axis, not changing its size. |
| center_horizontal | Place object in the horizontal center of its container, not changing its size. |
| center_vertical | Place object in the vertical center of its container, not changing its size. |
| clip_horizontal | Left and/or right edges of the child clipped to its container’s bounds based on the horizontal gravity. A left gravity will clip the right edge, a right gravity will clip the left edge, and neither will clip both edges. |
| clip_vertical | Top and/or bottom edges of the child clipped to its container’s bounds based on the vertical gravity. A top gravity will clip the bottom edge, a bottom gravity will clip the top edge, and neither will clip both edges. |
| start | Push object to the beginning of its container, not changing its size. |
| end | Push object to the end of its container, not changing its size. |
| left | Push object to the left of its container, not changing its size. |
| right | Push object to the right of its container, not changing its size. |
| top | Push object to the top of its container, not changing its size. |
| bottom | Push object to the bottom of its container, not changing its size. |
| fill | Grow the horizontal and vertical size of the object if needed so it completely fills its container. |
| fill_horizontal | Grow the horizontal size of the object if needed so it completely fills its container. |
| fill_vertical | Grow the vertical size of the object if needed so it completely fills its container. |
To specify multiple constraint, separate them by ‘|’.
Example
Below example demonstrate the impact of gravity constraint on android:gravity and android:layout_gravity.
<?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" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
android:background="#e3e2ad"
android:orientation="vertical">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:textSize="24sp"
android:text="gravity=" />
<TextView
android:layout_width="200dp"
android:layout_height="40dp"
android:background="#bcf5b1"
android:gravity="left"
android:text="left" />
<TextView
android:layout_width="200dp"
android:layout_height="40dp"
android:background="#aacaff"
android:gravity="center_horizontal"
android:text="center_horizontal" />
<TextView
android:layout_width="200dp"
android:layout_height="40dp"
android:background="#bcf5b1"
android:gravity="right"
android:text="right" />
<TextView
android:layout_width="200dp"
android:layout_height="40dp"
android:background="#aacaff"
android:gravity="center"
android:text="center" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"
android:background="#d6c6cd"
android:orientation="vertical" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:textSize="24sp"
android:text="layout_gravity=" />
<TextView
android:layout_width="200dp"
android:layout_height="40dp"
android:layout_gravity="left"
android:background="#bcf5b1"
android:text="left" />
<TextView
android:layout_width="200dp"
android:layout_height="40dp"
android:layout_gravity="center_horizontal"
android:background="#aacaff"
android:text="center_horizontal" />
<TextView
android:layout_width="200dp"
android:layout_height="40dp"
android:layout_gravity="right"
android:background="#bcf5b1"
android:text="right" />
<TextView
android:layout_width="200dp"
android:layout_height="40dp"
android:layout_gravity="center"
android:background="#aacaff"
android:text="center" />
</LinearLayout>
</LinearLayout>