android - 在 Android Studio 中，当我尝试启动我的应用程序时，它在 Android 模拟器中显示 "My First App has stopped"

Question

我认为是堆栈跟踪引起的。

我正在阅读官方 Android 应用构建教程:https://developer.android.com/training/index.html

我完成了“开始另一个 Activity ”部分并在尝试测试时发现了这个错误。我也无法在教程的前面部分运行该应用程序。

这让我找到了这个链接:Unfortunately MyApp has stopped. How can I solve this?

这让我找到了这个链接: What is a stack trace, and how can I use it to debug my application errors?

但我仍然无法弄明白。

这是错误日志的 fragment :

12-14 09:52:06.962 3696-3696/com.example.myfirstapp I/zygote:     at java.lang.Object java.lang.reflect.Method.invoke(java.lang.Object, java.lang.Object[]) (Method.java:-2)
12-14 09:52:06.962 3696-3696/com.example.myfirstapp I/zygote:     at void com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run() (RuntimeInit.java:438)
12-14 09:52:06.962 3696-3696/com.example.myfirstapp I/zygote:     at void com.android.internal.os.ZygoteInit.main(java.lang.String[]) (ZygoteInit.java:807)
12-14 09:52:06.962 3696-3696/com.example.myfirstapp D/AndroidRuntime: Shutting down VM
12-14 09:52:06.964 3696-3696/com.example.myfirstapp E/AndroidRuntime: FATAL EXCEPTION: main
                                                                      Process: com.example.myfirstapp, PID: 3696
                                                                      java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.myfirstapp/com.example.myfirstapp.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "com.example.myfirstapp.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/base.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_0_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_1_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_2_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_3_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_4_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_5_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_6_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_7_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_8_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_9_apk.apk"],nativeLibraryDirectories=[/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/lib/x86, /system/lib, /vendor/lib]]
                                                                          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2679)
                                                                          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
                                                                          at android.app.ActivityThread.-wrap11(Unknown Source:0)
                                                                          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
                                                                          at android.os.Handler.dispatchMessage(Handler.java:106)
                                                                          at android.os.Looper.loop(Looper.java:164)
                                                                          at android.app.ActivityThread.main(ActivityThread.java:6494)
                                                                          at java.lang.reflect.Method.invoke(Native Method)
                                                                          at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
                                                                          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
                                                                       Caused by: java.lang.ClassNotFoundException: Didn't find class "com.example.myfirstapp.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/base.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_0_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_1_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_2_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_3_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_4_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_5_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_6_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_7_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_8_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_9_apk.apk"],nativeLibraryDirectories=[/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/lib/x86, /system/lib, /vendor/lib]]
                                                                          at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:125)
                                                                          at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
                                                                          at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
                                                                          at android.app.Instrumentation.newActivity(Instrumentation.java:1174)
                                                                          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2669)
                                                                          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856) 
                                                                          at android.app.ActivityThread.-wrap11(Unknown Source:0) 
                                                                          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589) 
                                                                          at android.os.Handler.dispatchMessage(Handler.java:106) 
                                                                          at android.os.Looper.loop(Looper.java:164) 
                                                                          at android.app.ActivityThread.main(ActivityThread.java:6494) 
                                                                          at java.lang.reflect.Method.invoke(Native Method) 
                                                                          at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
                                                                          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) 
                                                                        Suppressed: java.lang.NoClassDefFoundError: Failed resolution of: Landroid/support/v7/app/AppCompatActivity;
                                                                          at java.lang.VMClassLoader.findLoadedClass(Native Method)
                                                                          at java.lang.ClassLoader.findLoadedClass(ClassLoader.java:738)
12-14 09:52:06.964 3696-3696/com.example.myfirstapp E/AndroidRuntime:     at java.lang.ClassLoader.loadClass(ClassLoader.java:363)
                                                                                ... 12 more
                                                                       Caused by: java.lang.ClassNotFoundException: Didn't find class "android.support.v7.app.AppCompatActivity" on path: DexPathList[[zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/base.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_0_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_1_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_2_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_3_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_4_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_5_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_6_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_7_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_8_apk.apk", zip file "/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/split_lib_slice_9_apk.apk"],nativeLibraryDirectories=[/data/app/com.example.myfirstapp-R68LcIdIMck0utpOhrKfsA==/lib/x86, /system/lib, /vendor/lib]]
                                                                          at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:125)
                                                                          at java.lang.ClassLoader.loadClass(ClassLoader.java:379)
                                                                          at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
                                                                                ... 15 more

关于如何解决这个问题有什么建议吗？谢谢!

编辑:

我相信这是我的 list 文件:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myfirstapp">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".DisplayMessageActivity"
            android:parentActivityName=".MainActivity" >
            <!-- The meta-data tag is required if you support API level 15 and lower -->
            android:name="android.support.PARENT_ACTIVITY"
            android:value=".MainActivity" />
        </activity>
    </application>

</manifest>

Answer 1

您的 list 中的结束标记不正确:

<activity android:name=".DisplayMessageActivity"
    android:parentActivityName=".MainActivity" >
    <!-- The meta-data tag is required if you support API level 15 and lower -->
    android:name="android.support.PARENT_ACTIVITY"
    android:value=".MainActivity" />
</activity>

这是没有开始标签的错误结束标签:

    <!-- The meta-data tag is required if you support API level 15 and lower -->
    android:name="android.support.PARENT_ACTIVITY"
    android:value=".MainActivity" />

尝试删除它。

更新:

在教程中，您缺少 <meta-data 的开放标记，因此您需要通过添加开放标记来更正它:

<meta-data android:name="android.support.PARENT_ACTIVITY" android:value=".MainActivity" />

添加标签后，你的代码会是这样的:

<activity android:name=".DisplayMessageActivity"
    android:parentActivityName=".MainActivity" >
    <!-- The meta-data tag is required if you support API level 15 and lower -->
    <meta-data android:name="android.support.PARENT_ACTIVITY"
    android:value=".MainActivity" />
</activity>