PercentRelativeLayout 的使用

PercentRelativeLayout, a recent addition to the Design Support Library, enables the ability to specify not only elements relative to each other but also the total percentage of available space. In the past, in order to position two elements next to each other with equal height, you would normally have to create a LinearLayout within a RelativeLayout.PercentRelativeLayout helps solves this issue.

To use, follow the setup guide and make sure the Gradle dependency is defined:

dependencies {    compile 'com.android.support:percent:23.1.0'}

The layout_width and layout_height of the PercentRelativeLayout should determine the total width and height that can be used. Any elements contained within it should specify the width and height possible using layout_heightPercent and/orlayout_widthPercent. Because this library is not part of the standard Android library, note that a custom attribute appnamespace being used.

An example of a layout used to describe the image above is shown below (taken from this sample code):

<android.support.percent.PercentRelativeLayout    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">    <View        android:id="@+id/top_left"        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_alignParentTop="true"        android:background="#ff44aacc"        app:layout_heightPercent="20%"        app:layout_widthPercent="70%" />    <View        android:id="@+id/top_right"        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_alignParentTop="true"        android:layout_toRightOf="@+id/top_left"        android:background="#ffe40000"        app:layout_heightPercent="20%"        app:layout_widthPercent="30%" />    <View        android:id="@+id/bottom"        android:layout_width="match_parent"        android:layout_height="0dp"        android:layout_below="@+id/top_left"        android:background="#ff00ff22"        app:layout_heightPercent="80%" /></android.support.percent.PercentRelativeLayout>

Margin Percentages

The margins can also be set to a percentage of the total widths as well:

• app:layout_marginStartPercent
• app:layout_marginEndPercent
• app:layout_marginTopPercent
• app:layout_marginBottomPercent

We can also define app:layout_marginPercent that will be to all four values above.

Aspect Ratio

Similar to how ImageView's adjustViewBounds:true can be used to scale the image according to its aspect ratio, we can also use PercentRelativeLayout to define an aspect ratio for a layout. If one dimension is set to 0dp and no percent scaling is associated with it, setting a percentage on the app:layout_aspectRatio attribute can scale the other to meet the ratio:

<android.support.percent.PercentRelativeLayout    xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:app="http://schemas.android.com/apk/res-auto"    android:background="#ff00ff22"    android:layout_width="match_parent"    android:layout_height="match_parent">    <!-- not using aspectRatio here -->    <View        android:id="@+id/view1"        android:background="#ff44aacc"        android:layout_width="300dp"        android:layout_height="wrap_content"        app:layout_heightPercent="50%"/>    <!-- using aspectRatio here -->    <View        android:layout_below="@id/view1"        android:background="#ffe40000"        android:layout_width="300dp"        android:layout_height="0dp"        app:layout_aspectRatio="160%"/></android.support.percent.PercentRelativeLayout>

The resulting layout appears as follows: