Com alguns problemas com o grandle files, tive que refazer e nisso recopiei os códigos exatamente nas respectivas pastas para continuar do ponto que parei, o SDK compila e executa no emulador, mas, quando eu aperto o botão de inserir "+" ele aparece este erro descrito no título e fecha a aplicação...
Logs do android Monitor
02-22 19:05:42.666 23947-23947/com.example.matheus.listaalunos E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.matheus.listaalunos, PID: 23947
android.content.ActivityNotFoundException: Unable to find explicit activity class {com.example.matheus.listaalunos/com.example.matheus.listaalunos.FormularioActivity}; have you declared this activity in your AndroidManifest.xml?
at android.app.Instrumentation.checkStartActivityResult(Instrumentation.java:1777)
at android.app.Instrumentation.execStartActivity(Instrumentation.java:1501)
at android.app.Activity.startActivityForResult(Activity.java:3745)
at android.support.v4.app.BaseFragmentActivityJB.startActivityForResult(BaseFragmentActivityJB.java:50)
at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:79)
at android.app.Activity.startActivityForResult(Activity.java:3706)
at android.support.v4.app.FragmentActivity.startActivityForResult(FragmentActivity.java:859)
at android.app.Activity.startActivity(Activity.java:4016)
at android.app.Activity.startActivity(Activity.java:3984)
at com.example.matheus.listaalunos.ListaAlunosActivity$1.onClick(ListaAlunosActivity.java:39)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
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)
