Kotlin- xmlns:app="http://schemas.android.com/apk/res-auto" 不可用

Question

I'm following the kotlin fundamentals code lab and in it it says that anything under API 21 will convert vector images to png images and to prevent that I need to add xmlns:app="http://schemas.android.com/apk/res-auto" to the activity_main.xml file and press Sync Now , and add vectorDrawables.useSupportLibrary = true to the defaultConfig { } in the .gradle(:app ) file. I followed everything but I kept getting an error:

/Users/Home/IdeaProjects/DiceRoller/app/src/main/res/layout/activity_main.xml:12

error: attribute android:srcCompat not found.

error: failed linking file resources.

I realized that the xmlns:app="http://schemas.android.com/apk/res-auto" line is grayed out

This is the gradle version I'm using:

dependencies {
    classpath 'com.android.tools.build:gradle:3.2.0-alpha18

What is causing this problem?

activity_main.xml file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    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="wrap_content"
    android:orientation="vertical"
    android:layout_gravity="center_vertical"
    tools:context=".MainActivity">

<android.support.v7.widget.AppCompatImageView 
           android:id="@+id/diceImageView"
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:layout_gravity="center_horizontal"
           android:srcCompat="@drawable/empty_dice"
           tools:src="@drawable/dice_1">
</android.support.v7.widget.AppCompatImageView>

build:grade(:app)

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.2"
    defaultConfig {
        applicationId "com.example.diceroller"
        minSdkVersion 19
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        vectorDrawables.useSupportLibrary = true
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation"org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'androidx.appcompat:appcompat:1.0.0-beta01'
    implementation 'androidx.core:core-ktx:1.2.0-beta02'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.2'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test:runner:1.1.0-alpha4'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.0-alpha4'
}

build.gradle:

buildscript {
    ext.kotlin_version = '1.3.50'
    repositories {
        google()
        jcenter()

    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.2.0-alpha18'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

allprojects {
    repositories {
        google()
        jcenter()

    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

Answer 1

This is because the srcCompat attribute only exists in the app ( http://schemas.android.com/apk/res-auto ) namespace for the AppCompatImageView class (see the API documentation for more info), not the default android ( http://schemas.android.com/apk/res/android ) namespace.

To fix this, simply rename the android portion of android:srcCompat to app:srcCompat :

<android.support.v7.widget.AppCompatImageView 
           app:srcCompat="@drawable/empty_dice" />

(PS Consider self-closing the XML tag such that you don't have to write more code to close the XML element. See this question for more info)