无法在Android Studio中使用CoordinatorLayout

Question

我的问题是，尽管在build.gradle文件中添加了所有可能的依赖项，但我仍无法在Android Studio中使用CoordinatorLayout。该类未实例化。这是我的build.gradle：

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.2"
    defaultConfig {
        applicationId "com.example.uiuxpractical4materialdesign"
        minSdkVersion 21
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
    implementation 'androidx.recyclerview:recyclerview:1.1.0'
    implementation 'com.google.android.material:material:1.0.0'
    implementation 'androidx.coordinatorlayout:coordinatorlayout:1.1.0'
}

activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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="match_parent"
    tools:context=".MainActivity">

    <androidx.coordinatorlayout.widget.CoordinatorLayout
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginStart="16dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="16dp"
        android:layout_marginBottom="16dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

错误：

java.lang.NoClassDefFoundError: androidx/coordinatorlayout/R$attr
    at androidx.coordinatorlayout.widget.CoordinatorLayout.<init>(CoordinatorLayout.java:211)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at org.jetbrains.android.uipreview.ViewLoader.createNewInstance(ViewLoader.java:403)
    at org.jetbrains.android.uipreview.ViewLoader.loadClass(ViewLoader.java:186)
    at org.jetbrains.android.uipreview.ViewLoader.loadView(ViewLoader.java:144)
    at com.android.tools.idea.rendering.LayoutlibCallbackImpl.loadView(LayoutlibCallbackImpl.java:309)
    at android.view.BridgeInflater.loadCustomView(BridgeInflater.java:418)
    at android.view.BridgeInflater.loadCustomView(BridgeInflater.java:429)
    at android.view.BridgeInflater.createViewFromTag(BridgeInflater.java:333)
    at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:730)
    at android.view.LayoutInflater.rInflate_Original(LayoutInflater.java:863)
    at android.view.LayoutInflater_Delegate.rInflate(LayoutInflater_Delegate.java:72)
    at android.view.LayoutInflater.rInflate(LayoutInflater.java:837)
    at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:824)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:515)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:394)
    at com.android.layoutlib.bridge.impl.RenderSessionImpl.inflate(RenderSessionImpl.java:323)
    at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:394)
    at com.android.tools.idea.layoutlib.LayoutLibrary.createSession(LayoutLibrary.java:200)
    at com.android.tools.idea.rendering.RenderTask.createRenderSession(RenderTask.java:572)
    at com.android.tools.idea.rendering.RenderTask.lambda$inflate$5(RenderTask.java:698)
    at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1590)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

由于这个原因，该类未实例化，我得到了这样的信息：-另外，这里也是错误的一小图：感谢大家为解决这个问题而提供的帮助。如果您还有其他需要，也请告知。

Answer 1

尝试添加以下依赖项实施'com.android.support:appcompat-v7:23.1.1'实施'com.android.support:design:23.1.1'

希望这对您有用。

Answer 2

尝试在build.gradle的依赖项中添加此行

implementation 'androidx.appcompat:appcompat:1.0.2'
implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
implementation 'com.android.support:design:29.0.2'
不用担心com.android .....和androidx ....之间的区别。如果您的android studio高于3.2，则会自动迁移实现。 

您可以检查此链接。https://stackoverflow.com/a/58619780/10075771它也可以帮助您了解情况：)希望我能对您有所帮助:)