Android Layouts


A Layout is a ViewGroup that defines the structure for a user interface in your application, such as in an activity .

Layouts are normally used as a template or structure to hold other elements. These elements are commonly wigets like button, textview, listview etc.

These elements will make up a hierarchy of views and ViewGroups objects.

The difference between a view and viewgroup is that a view will draw an element the user can interact with while a viewgroup will is just an invisible container for holding other views. Note that ViewGroups can be nested.

So in short a view is a widget while a viewgroup is layout.

Here are examples of Layouts/ViewGroups:

  1. RelativeLayout.
  2. LinearLayout.
  3. ConstraintLayout.
  4. FramewLayout.
  5. CordinatorLayout.

Android Layouts

Layout Declaration

You can declare a layout in two ways:

  1. (a) Declare UI elements in XML. Android provides a straightforward XML vocabulary that corresponds to the View classes and subclasses, such as those for widgets and layouts.
<?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" >
    <TextView android:id="@+id/myTextView"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="This is a TextView" />
    <Button android:id="@+id/myButton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Hello, I am a Button" />
</LinearLayout>

After you've declared your layout in XML, save the file with the .xml extension, in your Android project's res/layout/ directory, so it will properly compile.

(b). You can also use Android Studio's Layout Editor to build your XML layout using a drag-and-drop interface.

  1. Instantiate layout elements at runtime. Your app can create View and ViewGroup objects (and manipulate their properties) programmatically. #### LayoutParams All [ViewGroup](/android/viewgroup) (e.g. LinearLayout, [RelativeLayout](/android/relativelayout), CoordinatorLayout, etc.) have to store information about their children's properties. About the way its children are being laid out in the ViewGroup. This information is stored in objects of a wrapper class `ViewGroup.LayoutParams`. To include parameters specific to a particular layout type, the ViewGroups will use subclasses of `ViewGroup.LayoutParams` class. Here are examples: 1. LinearLayout : `LinearLayout.LayoutParams` 2. RelativeLayout : `RelativeLayout.LayoutParams` 3. CoordinatorLayout : `CoordinatorLayout.LayoutParams` etc. However most of the ViewGroups reutilize the ability to set margins for their children, such that rather than subclassing `ViewGroup.LayoutParams` directly, they subclass `ViewGroup.MarginLayoutParams` (which itself is a subclass of` ViewGroup.LayoutParams`). #### LayoutParams in xml LayoutParams objects are created based on the inflated layout xml file. ```xml ``` The parameters that begin with `layout_` specify how the enclosing layout should work. When the layout is inflated, those parameters are wrapped in a proper `LayoutParams` object, that later will be used by the Layout to properly position a particular [View](/android/view) within the [ViewGroup](/android/viewgroup). Other attributes of a View are directly View-related and are processed by the View itself. ### Top Android Layout Types Examples Let's look at some examples. .

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