在路径上找不到类“ retrofit2.Callback”：

Question

我在aar文件中使用改造，然后在我遇到改造方法时将那个aar文件导入应用程序中，它在出现logcat错误后会提示我

I/art: Rejecting re-init on previously-failed class java.lang.Class<com.example.mandatelibrary.MandateRegistrationActivity$2>: java.lang.NoClassDefFoundError: Failed resolution of: Lretrofit2/Callback;
        at void com.example.mandateapplication.MainActivity.btnCheckService(android.view.View) (MainActivity.java:59)
        at java.lang.Object java.lang.reflect.Method.invoke!(java.lang.Object, java.lang.Object[]) (Method.java:-2)
        at void android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(android.view.View) (AppCompatViewInflater.java:385)
        at boolean android.view.View.performClick() (View.java:5610)
        at void android.view.View$PerformClick.run() (View.java:22265)
        at void android.os.Handler.handleCallback(android.os.Message) (Handler.java:751)
        at void android.os.Handler.dispatchMessage(android.os.Message) (Handler.java:95)
        at void android.os.Looper.loop() (Looper.java:154)
I/art:     at void android.app.ActivityThread.main(java.lang.String[]) (ActivityThread.java:6077)
        at java.lang.Object java.lang.reflect.Method.invoke!(java.lang.Object, java.lang.Object[]) (Method.java:-2)
        at void com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run() (ZygoteInit.java:866)
        at void com.android.internal.os.ZygoteInit.main(java.lang.String[]) (ZygoteInit.java:756)
    Caused by: java.lang.ClassNotFoundException: Didn't find class "retrofit2.Callback" on path: DexPathList[[zip file "/data/app/com.example.mandateapplication-2/base.apk", zip file "/data/app/com.example.mandateapplication-2/split_lib_dependencies_apk.apk", zip file "/data/app/com.example.mandateapplication-2/split_lib_slice_0_apk.apk", zip file "/data/app/com.example.mandateapplication-2/split_lib_slice_1_apk.apk", zip file "/data/app/com.example.mandateapplication-2/split_lib_slice_2_apk.apk", zip file "/data/app/com.example.mandateapplication-2/split_lib_slice_3_apk.apk", zip file "/data/app/com.example.mandateapplication-2/split_lib_slice_4_apk.apk", zip file "/data/app/com.example.mandateapplication-2/split_lib_slice_5_apk.apk", zip file "/data/app/com.example.mandateapplication-2/split_lib_slice_6_apk.apk", zip file "/data/app/com.example.mandateapplication-2/split_lib_slice_7_apk.apk", zip file "/data/app/com.example.mandateapplication-2/split_lib_slice_8_apk.apk", zip file "/data/app/com.example.mandat
        at java.lang.Class dalvik.system.BaseDexClassLoader.findClass(java.lang.String) (BaseDexClassLoader.java:56)
        at java.lang.Class java.lang.ClassLoader.loadClass(java.lang.String, boolean) (ClassLoader.java:380)
        at java.lang.Class java.lang.ClassLoader.loadClass(java.lang.String) (ClassLoader.java:312)
        at void com.example.mandateapplication.MainActivity.btnCheckService(android.view.View) (MainActivity.java:59)
        at java.lang.Object java.lang.reflect.Method.invoke!(java.lang.Object, java.lang.Object[]) (Method.java:-2)
        at void android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(android.view.View) (AppCompatViewInflater.java:385)
        at boolean android.view.View.performClick() (View.java:5610)
        at void android.view.View$PerformClick.run() (View.java:22265)
        at void android.os.Handler.handleCallback(android.os.Message) (Handler.java:751)
        at void android.os.Handler.dispatchMessage(android.os.Message) (Handler.java:95)
I/art:     at void android.os.Looper.loop() (Looper.java:154)
        at void android.app.ActivityThread.main(java.lang.String[]) (ActivityThread.java:6077)
        at java.lang.Object java.lang.reflect.Method.invoke!(java.lang.Object, java.lang.Object[]) (Method.java:-2)
        at void com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run() (ZygoteInit.java:866)
        at void com.android.internal.os.ZygoteInit.main(java.lang.String[]) (ZygoteInit.java:756)