No resource identifier found for attribute 'layout_constraintLeft_toLeftOf' in package

Question

I am using the Android SDK 2.2.3. I am following a book on programming Android.

The code is:

<android.support.constraint.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:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="eu.a123sandberg.webview.MainActivity"
    tools:layout_editor_absoluteX="0dp"
    tools:layout_editor_absoluteY="81dp">

    <WebView
        android:layout_width="384dp"
        android:layout_height="511dp"
        tools:layout_editor_absoluteX="0dp"
        tools:layout_editor_absoluteY="0dp"
        app:layout_constraintLeft_toLeftOf="@+id/activity_main"
        tools:layout_constraintLeft_creator="0"
        app:layout_constraintTop_toTopOf="@+id/activity_main"
        tools:layout_constraintTop_creator="0"
        app:layout_constraintRight_toRightOf="@+id/activity_main"
        tools:layout_constraintRight_creator="0"
        app:layout_constraintBottom_toBottomOf="@+id/activity_main"
        tools:layout_constraintBottom_creator="0"
        />

</android.support.constraint.ConstraintLayout>

I have tried three different examples with the android.support.constraint.ConstraintLayout and in all cases do I get the same error message:

Error:(13) No resource identifier found for attribute 'layout_constraintLeft_toLeftOf' in package 'eu.a123sandberg.webview'

The build.gradle file contains:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 25
    buildToolsVersion "25.0.2"
    defaultConfig {
        applicationId "eu.a123sandberg.webview"
        minSdkVersion 21
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
                                                                                  testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-                   android.txt'), 'proguard-rules.pro'
        }
     }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-            core:2.2.2', {
    exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:25.1.1'
    testCompile 'junit:junit:4.12'
}

What do I have to do to resolve the error?

I have googled the error and not been able to find a suggestion that resolves the error.

Please help.

Answer 1

ConstraintLayout is not part of AppCompat. It's a standalone library.

Add the dependency in your build.gradle file

implementation 'com.android.support.constraint:constraint-layout:1.1.3' 

and click Sync now.