Group views in ConstraintLayout to treat them as a

问题:

I need to apply some constraints to a group of views in ConstraintLayout. I want to group these views and continue editing while the layout designer in Android studio treats them as a single view. Is there a way to do so without actually wrapping the views with a ViewGroup (another layout)? If such a wrapper is necessary, maybe there is a wrapper layout that comes with ConstraintLayout and allows to group objects without creating heavy layouts like RelativeLayout?

回答1:

ConstraintLayout Chains

Android developers recently released a new version of ConstraintLayout (1.0.2 as of today). This version contains a new major feature - Chains, which allows us to group views in ConstraintLayout.

Chains provide group-like behavior in a single axis (horizontally or vertically).

A set of widgets are considered a chain if they a linked together via a bi-directional connection

Once a chain is created, there are two possibilities:

• Spread the elements in the available space
• A chain can also be "packed", in that case the elements are grouped together

Currently, you need to use the following gradle dependency to use this feature (since it is an alpha):

 compile 'com.android.support.constraint:constraint-layout:1.0.0-alpha9'

Here you may find the newest version of ConstraintLayout to use in your projects.

Until Android Studio 2.3, Android Studio user interface designer did not support creating chains since you couldn't add bi-directional constraints in it. The solution was to create these constraints in manually XML, as mentioned by TranslucentCloud. From Android Studio 2.3 (currently only on canary channel), chains are supported in a UI editor as well (as GoRoS mentioned in comments).

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Example

Following is an example of how to position two views together in the middle of a screen using ConstraintLayout and chains:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    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">


    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="16dp"
        android:layout_marginStart="16dp"
        android:layout_marginTop="16dp"
        android:text="TextView"
        app:layout_constraintBottom_toTopOf="@+id/button"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.5"
        app:layout_constraintVertical_chainPacked="true"/>

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        android:layout_marginEnd="16dp"
        android:layout_marginStart="16dp"
        android:layout_marginTop="8dp"
        android:text="Button"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView"/>
</android.support.constraint.ConstraintLayout>

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Update (Jan, 2018) by @Mateus Gondim

In the recent versions, you should use app:layout_constraintVertical_chainStyle="packed" instead of app:layout_constraintVertical_chainPacked="true"

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回答2:

You can use

android.support.constraint.Guideline

to group elements together.

Add a Guideline (vertical or horizontal) and then use that as an anchor for the other views. Here is a simple example of horizontally centering two grouped textviews: (showing design view in AS)

<?xml version="1.0" encoding="utf-8"?>
<ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"
    android:layout_height="56dp"
    android:background="@android:color/white"
    android:paddingLeft="16dp"
    android:paddingRight="16dp">


    <TextView
        android:id="@+id/top_text"
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:background="@android:color/holo_red_light"
        android:textSize="16sp"
        app:layout_constraintBottom_toTopOf="@+id/guideline"
        android:text="Above"
        tools:text="Above" />

    <android.support.constraint.Guideline
        android:id="@+id/guideline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.5" />

    <TextView
        android:id="@+id/bottom_text"
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:background="@android:color/holo_blue_bright"
        android:textSize="16sp"
        app:layout_constraintTop_toBottomOf="@+id/guideline"
        android:text="Below"
        tools:text="Below" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:text="Right vertically centered"
        android:textSize="24sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="Right vertically centered"/>
</ConstraintLayout>