Mumbai University > Information Technology > Sem 5 > Open Source Technology

Marks: 5M

Year: Dec 2015

The Android SDK includes the following layout views that may be used within an Android user interface design:

• LinearLayout – Positions child views in a single row or column depending on the orientation selected. A weight value can be set on each child to specify how much of the layout space that child should occupy relative to other children.
• TableLayout – Arranges child views into a grid format of rows and columns. Each row within a table is represented by a TableRow object child, which, in turn, contains a view object for each cell.
• FrameLayout – The purpose of the FrameLayout is to allocate an area of screen, typically for the purposes of displaying a single view. If multiple child views are added they will, by default, appear on top of each other positioned in the top left hand corner of the layout area. Alternate positioning of individual child views can be achieved by setting gravity values on each child. For example, setting a center_vertical gravity on a child will cause it to be positioned in the vertical center of the containing FrameLayout view.
• RelativeLayout – Probably the most powerful and flexible of the layout managers, this allows child views to be positioned relative both to each other and the containing layout view through the specification of alignments and margins on child views. For example, child View A may be configured to be positioned in the vertical and horizontal center of the containing RelativeLayout view. View B, on the other hand, might also be configured to be centered horizontally within the layout view, but positioned 30 pixels above the top edge of View A, thereby making the vertical position relative to that of View A. The RelativeLayout manager can be of particular use when designing a user interface that must work on a variety of screen sizes and orientations.
• AbsoluteLayout – Allows child views to be positioned at specific X and Y coordinates within the containing layout view. Use of this layout is discouraged since it lacks the flexibility to respond to changes in screen size and orientation.
• GridLayout – The GridLayout is a relatively new layout manager that was introduced as part of Android 4.0. A GridLayout instance is divided by invisible lines that form a grid containing rows and columns of cells. Child views are then placed in cells and may be configured to cover multiple cells both horizontally and vertically allowing a wide range of layout options to be quickly and easily implemented. Gaps between components in a GridLayout may be implemented by placing a special type of view called a Space view into adjacent cells, or by setting margin parameters.

When considering the use of layouts in the user interface for an Android application it is worth keeping in mind that, as will be outlined in the next section, these can be nested within each other to create a user interface design of just about any necessary level of complexity.