在Android L preview上运行示例应用程序时出现异常

我尝试从Android L preview sdk目录运行两个示例应用程序。 每当我在Emulator或设备上运行时，我都会遇到以下异常，其中闪现了最新的图像

06-27 11:33:12.627: E/AndroidRuntime(1071): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.elevationdrag/com.example.android.elevationdrag.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "com.example.android.elevationdrag.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.android.elevationdrag-1.apk"],nativeLibraryDirectories=[/data/app-lib/com.example.android.elevationdrag-1, /vendor/lib, /system/lib]]
06-27 11:33:12.627: E/AndroidRuntime(1071):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2166)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2317)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at android.app.ActivityThread.access$800(ActivityThread.java:143)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1258)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at android.os.Handler.dispatchMessage(Handler.java:102)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at android.os.Looper.loop(Looper.java:135)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at android.app.ActivityThread.main(ActivityThread.java:5070)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at java.lang.reflect.Method.invoke(Native Method)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at java.lang.reflect.Method.invoke(Method.java:372)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:836)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:631)
06-27 11:33:12.627: E/AndroidRuntime(1071): Caused by: java.lang.ClassNotFoundException: Didn't find class "com.example.android.elevationdrag.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.android.elevationdrag-1.apk"],nativeLibraryDirectories=[/data/app-lib/com.example.android.elevationdrag-1, /vendor/lib, /system/lib]]
06-27 11:33:12.627: E/AndroidRuntime(1071):     at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at android.app.Instrumentation.newActivity(Instrumentation.java:1062)
06-27 11:33:12.627: E/AndroidRuntime(1071):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2157)
06-27 11:33:12.627: E/AndroidRuntime(1071):     ... 10 more
06-27 11:33:12.627: E/AndroidRuntime(1071):     Suppressed: java.lang.ClassNotFoundException: com.example.android.elevationdrag.MainActivity
06-27 11:33:12.627: E/AndroidRuntime(1071):         at java.lang.Class.classForName(Native Method)
06-27 11:33:12.627: E/AndroidRuntime(1071):         at java.lang.BootClassLoader.findClass(ClassLoader.java:781)
06-27 11:33:12.627: E/AndroidRuntime(1071):         at java.lang.BootClassLoader.loadClass(ClassLoader.java:841)
06-27 11:33:12.627: E/AndroidRuntime(1071):         at java.lang.ClassLoader.loadClass(ClassLoader.java:504)
06-27 11:33:12.627: E/AndroidRuntime(1071):         ... 13 more
06-27 11:33:12.627: E/AndroidRuntime(1071):     Caused by: java.lang.NoClassDefFoundError: Class "Lcom/example/android/elevationdrag/MainActivity;" not found

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有人知道如何修复它吗？

我可以通过从下载并将buildToolsVersion更改为20.0.0来运行此示例。