Question

我正在尝试将CardView实现到我的Android布局中，这给我一个渲染问题。

'以下类无法实例化' - android.support.v7.widget.CardView

activity_overview.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    tools:context="com.example.myapp.OverviewActivity">

    <android.support.v7.widget.CardView
        xmlns:card_view="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <TextView
                android:id="@+id/username"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:text="@string/app_name" />
        </LinearLayout>
    </android.support.v7.widget.CardView>
</LinearLayout>

app.gradle

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-v7:24.2.1'
    compile 'com.android.support:cardview-v7:24.2.1'
    compile 'com.android.support:recyclerview-v7:24.2.1'
    compile 'com.google.firebase:firebase-core:9.6.1'
    compile 'com.google.firebase:firebase-auth:9.6.1'
    compile 'com.google.firebase:firebase-crash:9.6.1'
    compile 'com.google.firebase:firebase-database:9.6.1'

    testCompile 'junit:junit:4.12'
}

例外详细信息

java.lang.ClassNotFoundException: android.support.v7.cardview.R$color
    at org.jetbrains.android.uipreview.ModuleClassLoader.load(ModuleClassLoader.java:160)
    at com.android.tools.idea.rendering.RenderClassLoader.findClass(RenderClassLoader.java:54)
    at org.jetbrains.android.uipreview.ModuleClassLoader.findClass(ModuleClassLoader.java:90)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at org.jetbrains.android.uipreview.ModuleClassLoader.loadClass(ModuleClassLoader.java:193)
    at android.support.v7.widget.CardView.initialize(CardView.java:232)
    at android.support.v7.widget.CardView.<init>(CardView.java:116)
    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:465)
    at org.jetbrains.android.uipreview.ViewLoader.loadClass(ViewLoader.java:172)
    at org.jetbrains.android.uipreview.ViewLoader.loadView(ViewLoader.java:105)
    at com.android.tools.idea.rendering.LayoutlibCallbackImpl.loadView(LayoutlibCallbackImpl.java:186)
    at android.view.BridgeInflater.loadCustomView(BridgeInflater.java:334)
    at android.view.BridgeInflater.loadCustomView(BridgeInflater.java:345)
    at android.view.BridgeInflater.createViewFromTag(BridgeInflater.java:245)
    at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:727)
    at android.view.LayoutInflater.rInflate_Original(LayoutInflater.java:858)
    at android.view.LayoutInflater_Delegate.rInflate(LayoutInflater_Delegate.java:70)
    at android.view.LayoutInflater.rInflate(LayoutInflater.java:834)
    at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:821)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:518)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
    at com.android.layoutlib.bridge.impl.RenderSessionImpl.inflate(RenderSessionImpl.java:324)
    at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:429)
    at com.android.ide.common.rendering.LayoutLibrary.createSession(LayoutLibrary.java:389)
    at com.android.tools.idea.rendering.RenderTask$2.compute(RenderTask.java:548)
    at com.android.tools.idea.rendering.RenderTask$2.compute(RenderTask.java:533)
    at com.intellij.openapi.application.impl.ApplicationImpl.runReadAction(ApplicationImpl.java:966)
    at com.android.tools.idea.rendering.RenderTask.createRenderSession(RenderTask.java:533)
    at com.android.tools.idea.rendering.RenderTask.lambda$inflate$72(RenderTask.java:659)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

Answer 1

首先将CardView添加到gradle文件，然后执行Build＆gt;清洁项目

Answer 2

如果您创建一个新文件，那么您将注意到针对recyclerView和cardView的下载按钮，只需单击即可进行准备。无需从android studio社区获取互联网链接，因为它支持较旧版本的android studio。

CardView无法渲染 - ClassNotFoundException：android.support.v7.cardview.R $ color

2 个答案: