App Engine：应用程序在尝试访问CloudBackendFragment类时崩溃

Question

我正在使用谷歌提供的Mobile Backend启动器。我已经添加了自己的活动，我正在使用 CloudBackend 和 CloudBackendFragment 类。当我尝试打开活动时，它会崩溃。我认为这是因为我在onCreate方法中初始化的CloudBackendFragment对象。但是根据示例留言簿活动，我需要它来执行插入和查询数据存储区。 代码

public class Regform extends Activity implements OnListener{
private CloudBackendFragment mProcessingFragment1;
private FragmentManager mFragmentManager;
private Button register;
private Button show;
private static final String PROCESSING_FRAGMENT_TAG = "BACKEND_FRAGMENT";
private static final String TAG="Registration";

@Override
protected void onCreate(Bundle savedInstanceState) {
    Log.i(TAG,"Entered the onCreate method");
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_regform);
    final EditText firstName = (EditText) findViewById(R.id.firstName);

    final EditText lastName = (EditText) findViewById(R.id.lastName);

    final EditText email = (EditText) findViewById(R.id.email);

    final EditText phoneNumber = (EditText) findViewById(R.id.phone);

    final EditText username = (EditText) findViewById(R.id.userName);

    final EditText password = (EditText) findViewById(R.id.password);

    register = (Button) findViewById(R.id.register);
    show=(Button) findViewById(R.id.Show);
    final Button login = (Button) findViewById(R.id.login);
    mFragmentManager=getFragmentManager();
    FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();

     mProcessingFragment1 = (CloudBackendFragment) mFragmentManager.
                findFragmentByTag(PROCESSING_FRAGMENT_TAG);
        // If not retained (or first time running), create a new one
        if (mProcessingFragment1 == null) {
            mProcessingFragment1 = new CloudBackendFragment();
            mProcessingFragment1.setRetainInstance(true);
            fragmentTransaction.add(mProcessingFragment1, PROCESSING_FRAGMENT_TAG);

        }
        fragmentTransaction.commit();

register.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View view) {

            Log.i(TAG,"Entered the regiter method");
            CloudEntity reg = new CloudEntity("Registration");
            reg.put("FirstName", firstName.getText().toString());
            reg.put("LastName", lastName.getText().toString());
            reg.put("Email", email.getText().toString());
            reg.put("phoneno", phoneNumber.getText());
            reg.put("username",username.getText().toString());
            reg.put("password",password.getText().toString());
            CloudCallbackHandler<CloudEntity> handler = new CloudCallbackHandler<CloudEntity>() {
                @Override
                public void onComplete(final CloudEntity result) {

                    firstName.setText("");
                    lastName.setText("");
                    email.setText("");
                    phoneNumber.setText("");
                    firstName.setEnabled(true);
                    lastName.setEnabled(true);
                    email.setEnabled(true);
                    phoneNumber.setEnabled(true);
                    register.setEnabled(true);
                    password.setEnabled(true);
                    username.setEnabled(true);
                }


                @Override
                public void onError(final IOException exception) {
                    handleEndpointException(exception);
                }
            };

            // execute the insertion with the handler
            mProcessingFragment1.getCloudBackend().insert(reg, handler);
            firstName.setEnabled(false);
            lastName.setEnabled(false);
            email.setEnabled(false);
            phoneNumber.setEnabled(false);
            register.setEnabled(false);
        }

    });

我对app引擎和android都比较新。请帮帮我。