Essential Android Layouts edit forum

Percent Layouts

The Percent Support Library provides PercentFrameLayout and PercentRelativeLayout, two ViewGroups that provide an easy way to specify View dimensions and margins in terms of a percentage of the overall size.

You can use the Percent Support Library by adding the following to your dependencies.

compile 'com.android.support:percent:25.3.1'

If you wanted to display a view that fills the screen horizontally but only half the screen vertically you would do thie following.

<android.support.percent.PercentFrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <FrameLayout
        app:layout_widthPercent="100%"
        app:layout_heightPercent="50%"
        android:background="@android:color/black" />

<android.support.percent.PercentFrameLayout>

You can also define the percentages in a separate XML file with code such as:

<fraction name="margin_start_percent">25%</fraction>

And refer to them in your layouts with @fraction/margin_start_percent.

They also contain the ability to set a custom aspect ratio via app:layout_aspectRatio.

This allows you to set only a single dimension, such as only the width, and the height will be automatically determined based on the aspect ratio you’ve defined, whether it is 4:3 or 16:9 or even a square 1:1 aspect ratio.

For example:

<ImageView
   app:layout_widthPercent="100%"
   app:layout_aspectRatio="178%"
   android:scaleType="centerCrop"
   android:src="@drawable/header_background"/>

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