Android studio NoClassDefFoundError - android.support.v7.app.AppCompatDelegateImplV14

Question

我已将项目从Eclipse升级到Android工作室.应用程序启动后,我收到以下错误

java.lang.NoClassDefFoundError: android.support.v7.app.AppCompatDelegateImplV14
            at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:93)
            at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:77)
            at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:429)
            at android.support.v7.app.AppCompatActivity.onCreate(AppCompatActivity.java:57)
            at com.lib.base.NBaseActionBarActivity.onCreate(NBaseActionBarActivity.java:39)
            at com.app.home.HomeFragmentActivity.onCreate(HomeFragmentActivity.java:254)
            at android.app.Activity.performCreate(Activity.java:5990)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
            at android.app.ActivityThread.access$800(ActivityThread.java:151)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5254)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

是什么导致这个问题？我已将appcompat v7添加到gradle中,

compile 'com.android.support:appcompat-v7:22.2.0'

提前致谢.