06-20 09:30:54.397 12442-12442/com.example.android.bakingapp E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.android.bakingapp, PID: 12442
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.bakingapp/com.example.android.bakingapp.ui.DetailActivity}: java.lang.ClassCastException: com.example.android.bakingapp.ui.DetailActivity cannot be cast to com.example.android.bakingapp.adapters.StepAdapter$StepListener
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
        at android.app.ActivityThread.-wrap12(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6077)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
     Caused by: java.lang.ClassCastException: com.example.android.bakingapp.ui.DetailActivity cannot be cast to com.example.android.bakingapp.adapters.StepAdapter$StepListener
        at com.example.android.bakingapp.ui.MainFragment.displayRecipeSteps(MainFragment.java:168)
        at com.example.android.bakingapp.ui.MainFragment.onCreateView(MainFragment.java:139)
        at android.support.v4.app.Fragment.performCreateView(Fragment.java:2346)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1428)
        at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1759)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1827)
        at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:797)
        at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2596)
        at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2383)
        at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2338)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2245)
        at android.support.v4.app.FragmentManagerImpl.dispatchStateChange(FragmentManager.java:3248)
        at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:3200)
        at android.support.v4.app.FragmentController.dispatchActivityCreated(FragmentController.java:195)
        at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:597)
        at android.support.v7.app.AppCompatActivity.onStart(AppCompatActivity.java:177)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1248)
        at android.app.Activity.performStart(Activity.java:6679)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2609)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
        at android.app.ActivityThread.-wrap12(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6077)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)