代码适用于Android工作室模拟器，但不适用于Android手机

Question

我写了一个简单的登录程序，在Android Studio Emulator上测试它，它工作正常。 然后我尝试使用我的手机进行调试，并在按下发送按钮后立即崩溃。 这是代码：

public class MainActivity extends AppCompatActivity implements LoginFrag.PinManager {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    LoginFrag fragment = new LoginFrag();
            getFragmentManager()
                    .beginTransaction()
                    .add(R.id.main_frame_layout, fragment)
                    .commit();
}
@Override
public void checkPin(int i) {
    int pin = i;
    if (pin!=123){
        Toast.makeText(this, "Wrong password", Toast.LENGTH_LONG).show();
    }
    else {
        loadMenu(); 
    }

}


public class LoginFrag extends Fragment {

private Button button;
private EditText editText;
PinManager pinActivity;

public interface PinManager{
    public void checkPin(int i);
}
@Override
public void onAttach(Context context) {
    super.onAttach(context);
    try {
        pinActivity = (PinManager) context;
    } catch (ClassCastException e){
        throw new ClassCastException(context.toString());
    }
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.login_frag, container, false);
    button = (Button) view.findViewById(R.id.login_button);
    editText = (EditText) view.findViewById(R.id.pin);
    button.setOnClickListener(
            new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    pinReader(v);
                }
            }
    );
    return view;
}
public void pinReader(View v){
    pinActivity.checkPin(Integer.parseInt(editText.getText().toString()));
    editText.setText("");
    }
}

错误如下：

W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x41781e48)
E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.example.max.passwordmanager, PID: 13259
              java.lang.NullPointerException
                  at com.example.max.passwordmanager.LoginFrag.pinReader(LoginFrag.java:57)
                  at com.example.max.passwordmanager.LoginFrag$1.onClick(LoginFrag.java:47)
                  at android.view.View.performClick(View.java:4461)
                  at android.view.View$PerformClick.run(View.java:18523)
                  at android.os.Handler.handleCallback(Handler.java:733)
                  at android.os.Handler.dispatchMessage(Handler.java:95)
                  at android.os.Looper.loop(Looper.java:136)
                  at android.app.ActivityThread.main(ActivityThread.java:5118)
                  at java.lang.reflect.Method.invokeNative(Native Method)
                  at java.lang.reflect.Method.invoke(Method.java:515)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:606)
                  at dalvik.system.NativeStart.main(Native Method)
I/Process: Sending signal. PID: 13259 SIG: 9
Application terminated.

我在两个手机上运行了代码，一个用android 4.4.2，另一个用android 5.0.2，一旦你点击按钮发送引脚就会崩溃。