Gravity is an android method for aligning view in a layout. There are two kinds of gravity, gravity and layout gravity. Basically a gravity is set in xml layout files, but you can also set a gravity of any view in java source code. To set gravity in xml use [cci]android:layout_gravity[/cci] and [cci]android:gravity[/cci] attributes. The values of both attributes is combination of the following constants:
| 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. |
| 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. |
| center_vertical | : Place object in the vertical center of its container, not changing its size. |
| fill_vertical | : Grow the vertical size of the object if needed so it completely fills its container. |
| center_horizontal | : Place object in the horizontal center of its container, not changing its size. |
| fill_horizontal | : Grow the horizontal size of the object if needed so it completely fills its container. |
| center | : Place the object in the center of its container in both the vertical and horizontal axis, not changing its size. |
| fill | : Grow the horizontal and vertical size of the object if needed so it completely fills its container. |
| clip_vertical | : Additional option that can be set to have the top and/or bottom edges of the child clipped to its container’s bounds. The clip will be 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. |
| clip_horizontal | : Additional option that can be set to have the left and/or right edges of the child clipped to its container’s bounds. The clip will be 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. |
| 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. |
android:gravity attribute
[cci]android:gravity[/cci] will set alignment to the content of a view. This aligment will only take effect if size of view is bigger than view’s content. Maybe you got confuse, what is the different between view and view content. Consider a button view below.
Button View
As you can see from image above, the button view is the rectangle boundary of a button, while the content of the button view is the text “button” it self.
Now, we will align the content of the button to bottom right of the button. To align content to bottom right we add [cci]android:gravity=”bottom|right”[/cci] attribute.
[sourcecode lang=”xml” highlight=”12″]
<?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" >
<Button
android:id="@+id/button1"
android:layout_width="match_parent"
android:layout_height="70dp"
android:text="Button"
android:gravity="bottom|right" />
</LinearLayout>
[/sourcecode]
Will result as follow:
Content of button view aligned to bottom right
android:layout_gravity attribute
[cci]android:layout_gravity[/cci] is used to align view child to its parent. Note that this attribute will only take effect if the parent is [cci]LinearLayout[/cci] and the size of child smaller than parent size.
Now we will align a button to the right of parent. To do this, we must add [cci]android:layout_gravity=”right”[/cci] attribute.
[sourcecode lang=”xml” highlight=”12″]
<?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" >
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button"
android:layout_gravity="right" />
</LinearLayout>
[/sourcecode]
The result is as follow:
Button view is aligned to right
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