How To Make Sense Of The Many Android Layouts

As an Android developer, you have likely encountered the wide variety of layout options available and wondered which one is the right choice for your app. From LinearLayout to ConstraintLayout, the options can seem endless and confusing. This guide will walk you through the most common Android layouts, when you should use them, and how to implement them effectively.

The Building Blocks: Views and ViewGroups

Before diving into specific layout types, it‘s important to understand Views and ViewGroups.

Views are the basic building blocks of UI elements in Android. A TextView that displays text or an ImageView that shows an image are examples of Views.

ViewGroups are containers that hold Views and other ViewGroups. ViewGroups define the layout structure and organization of their child views. The various Android layout types like LinearLayout and RelativeLayout are subclasses of the ViewGroup class.

ViewGroups and Views relate to each other in a parent-child hierarchy, with the ViewGroup as the parent managing the layout of the child Views.

Measure, Layout, Draw Lifecycle

When an Android app loads a layout resource file, it constructs a View hierarchy from the XML. This hierarchy then goes through 3 key phases:

Measure: The parent ViewGroup iterates through its child views to determine constraints and measurements
Layout: Based on measurements, views are assigned exact positions and sizes
Draw: Views draw themselves and any child views based on the layout specifications

This lifecycle repeats anytime the app needs to redraw the layout, such as on device rotation. Optimizing performance means keeping your layout hierarchy shallow when possible.

Common Android Layout Types

Now let‘s explore some of the most widely used Android layouts.

LinearLayout

As the name suggests, LinearLayout organizes its child views into a single vertical or horizontal orientation. The android:orientation property sets direction, with "vertical" and "horizontal" as options.

Here is a simple vertical LinearLayout:

<LinearLayout 
   android:orientation="vertical"
   android:layout_width="match_parent"
   android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:text="Text View 1"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:text="Text View 2"/>

</LinearLayout>

A key advantage of LinearLayout is the layout_weight attribute. This defines how much space each child view should occupy relative to siblings. For example:

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_weight="1" 
        android:layout_width="0dp"
        android:layout_height="wrap_content"/>

    <TextView 
        android:layout_weight="3"
        android:layout_width="0dp"
        android:layout_height="wrap_content"/>

</LinearLayout>

Here the second TextView gets 3x the space compared to the first. layout_weight allows flexible scaling across different device sizes.

LinearLayout offers simplicity and performance, but can get deeply nested when attempting complex layouts.

RelativeLayout

As the name implies, RelativeLayout positions child views in relation to each other or the parent layout. For example:

<RelativeLayout 
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Text View 1"
        android:id="@+id/textview1"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:text="Text View 2"
        android:layout_below="@id/textview1"/>

</RelativeLayout>

Here layout_below positions the second TextView below the first. Useful RelativeLayout features include:

layout_toLeftOf
layout_toRightOf
layout_above
layout_alignParentTop
layout_centerHorizontal
layout_centerInParent

And many more. This allows crafting UIs with minimal nesting. A drawback is RelativeLayout complexity can impact performance from repeated measuring.

ConstraintLayout

ConstraintLayout shares similarities with RelativeLayout in declaring views in relation to each other or the parent layout. But the underlying system differs using Constraints rather than relative positioning:

<androidx.constraintlayout.widget.ConstraintLayout  
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/button1"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/button2"
        app:layout_constraintStart_toEndOf="@id/button1"
        app:layout_constraintTop_toTopOf="@id/button1" 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</androidx.constraintlayout.widget.ConstraintLayout>

Here constraints position the Buttons relative to the parent ConstraintLayout and each other. Benefits vs RelativeLayout:

Arranging views based on mathematical constraints vs relative positions
Increased performance through optimized measuring
Easier building responsive UIs

The visual editor also helps craft constraints faster. Overall ConstraintLayout brings big gains in building more complex layouts.

FrameLayout & FragmentLayout

Sometimes you need a dedicated container like FrameLayout for holding a single child view. It draws its bounds around that one View. The child expands as needed, like a photo inside a frame:

<FrameLayout
    android:layout_width="match_parent" 
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</FrameLayout>

FrameLayout works well for situational needs like displaying a fragment inside an activity. But it quickly gets unwieldy if holding multiple views that can overlap.

The Fragment container FragmentLayout offers similar single-view functionality optimized for holding fragments specifically.

ListView & GridView

ListView and GridView enable vertically scrolling lists and gridsperfect for long lists like contacts or grid-based content like a photo gallery. Defining static Views for hundreds of rows or columns would be tedious and inefficient.

Instead, ListView & GridView work by recycling existing Views with new data as the user scrolls. This View recycling mechanism makes them extremely efficient even for huge datasets, a process managed by adapters.

Benefits include:

Displaying unlimited rows/columns smoothly
View recycling for performance
Easy binding to dynamic data sources

With some key layout fundamentals covered, you have the knowledge to make informed decisions between options like LinearLayout and ConstraintLayout based on your app’s needs. Remember to keep layout hierarchies shallow, leverage profiles for responsiveness, and utilize tools like the visual editor. Mastering Android layouts takes time, but pays huge dividends in building effective user experiences.