Although Android offers a variety of widgets to provide small and re-usable interactive elements, you might also need to re-use larger components that require a special layout. To efficiently re-use complete layouts, you can use the and tags to embed another layout inside the current layout.
Reusing layouts is particularly powerful as it allows you create reusable complex layouts. For example, a yes/no button panel, or custom progress bar with description text. It also means that any elements of your application that are common across multiple layouts can be extracted, managed separately, then included in each layout. So while you can create individual UI components by writing a custom
Create a Re-usable Layout
If you already know the layout that you want to re-use, create a new XML file and define the layout. For example, here's a layout from the G-Kenya codelab that defines a title bar to be included in each activity (titlebar.xml):
The root
Use the Tag
Inside the layout to which you want to add the re-usable component, add the tag. For example, here's a layout from the G-Kenya codelab that includes the title bar from above:
Here's the layout file:
...
You can also override all the layout parameters (any android:layout_* attributes) of the included layout's root view by specifying them in the tag. For example:
However, if you want to override layout attributes using the tag, you must override both android:layout_height and android:layout_width in order for other layout attributes to take effect.
Use the Tag
The tag helps eliminate redundant view groups in your view hierarchy when including one layout within another. For example, if your main layout is a vertical
To avoid including such a redundant view group, you can instead use the element as the root view for the re-usable layout. For example:
Now, when you include this layout in another layout (using the tag), the system ignores the element and places the two buttons directly in the layout, in place of the tag.