Android Layouts

Layouts

• Layouts are subclasses of the ViewGroup class.
• A typical layout defines the visual structure for an Android user interface and can be created either at run time using View/ ViewGroup objects or we can declare our layout using a simple XML file which is located in the res/layout folder of our project.

Layouts Types

• There are several types of Layouts that will be used in almost all Android applications to provide a different view, look, and feel. These are:-
  • Linear Layout
    • LinearLayout is a view group that aligns or arranges all children in a single direction, vertically or horizontally.
  • Relative Layout
    • RelativeLayout is a view group that displays child views in relative positions i.e., Positions child views relative to each other or relative to the parent view..
  • Constraint Layout
    • Allows creating complex layouts by setting constraints between views, offering flexibility and responsiveness.
    • Android Constraint Layout is used to define a layout by assigning constraints for every child view/widget relative to other views present.
    • A Constraint Layout is similar to a relative layout but with more power.
    • The aim of Constraint Layout is to improve the performance of the applications by removing the nested views with a flat and flexible design.
    • A view inside the Constraint Layout has handles(or anchor points) on each side which are used to assign the constraints. 
  • Absolute Layout
    • • Absolute Layout enables to specify the exact location of its child views.
  • Frame Layout
    • The Frame Layout is a placeholder on the screen that is used to display more than one view as a single view.
    • Places child views on top of each other, often used for simple container layouts.
  • List View
    • ListView is a viewgroup that displays a list of scrollable items.
  • Grid View
    • GridView is a ViewGroup that displays items in a two-dimensional, scrollable grid.
  • Table Layout
    • TableLayout is a view that groups views into rows and columns.

Layouts Attributes

• Each layout has a set of attributes that define the visual properties of that layout.
• There are few common attributes among all the layouts and there are other attributes that are specific to that layout. These are –
  • android: id
    • This is the ID that uniquely identifies the view that is used in coding for calling or representing it.
  • android:layout_width
    • This attribute represents the width of the layout.
    • android:layout_width=wrap_content tells about the view occupying the size itself to the dimensions required by its content.
    • android:layout_width=fill_parent tells about the view to become as big as its parent view.

  • android:layout_height

    • This attribute represents the height of the layout
  • android:layout_marginTop
    • This attribute represents the extra space on the top side of the layout.
  • android:layout_marginBottom
    • This attribute represents the extra space on the bottom side of the layout.
  • android:layout_marginLeft
    • This attribute represents the extra space on the left side of the layout.
  • android:layout_marginRight
    • This attribute represents the extra space on the right side of the layout.
  • android:layout_gravity
    • This attribute represents how child Views are positioned either horizontally or vertically.
  • android:layout_weight
    • This specifies how much of the extra space in the layout should be allocated to the View.
  • android:layout_x
    • This specifies the x-coordinate of the layout.
  • android:layout_y
    • This specifies the y-coordinate of the layout.
  • android:layout_width
    • This attribute represents the width of the layout.
  • android:padding-left
    • This attribute represents the left padding filled for the layout.
  • android:padding-right
    • This attribute represents the right padding filled for the layout.
  • android:paddingTop
    • This attribute represents the top padding filled for the layout.
  • android:padding-bottom
    • This attribute represents the bottom padding filled for the layout.

Units Used in Layouts Attributes

• dp (Density-independent Pixels):
• sp ( Scale-independent Pixels):
• pt ( Points which is 1/72 of an inch):
• px( Pixels):
• mm ( Millimeters):
• in (inches):