Android MVVM 存储库和 ViewModel 问题

Question

I have just start my MVVM pattern. And when I do the login, I have some problems. Here is my code.

1. login service

public interface LoginService {
    @FormUrlEncoded
    @POST("user/login")
    Call<JsonObject> validateLogin(@Field("phoneNum") String phoneNum, @Field("password") String password);
}

2. Repository

public class LoginRepository {
    private static final String TAG = "LoginRepository";
    private static LoginRepository instance;

    public static LoginRepository getInstance() {
        if (instance == null) {
            instance = new LoginRepository();
        }
        return instance;
    }

    public MutableLiveData<JsonObject> getLoginMessage(String phoneNum, String password) {
        final MutableLiveData<JsonObject> message = new MutableLiveData<>();
        LoginService service = RetrofitClass.getLoginService();
        Call<JsonObject> call = service.validateLogin(phoneNum, password);
        call.enqueue(new Callback<JsonObject>() {
            @Override
            public void onResponse(Call<JsonObject> call, Response<JsonObject> response) {
                if (response.isSuccessful()) {
                    JsonObject info = response.body();
                    message.setValue(info);
                }
            }

            @Override
            public void onFailure(Call<JsonObject> call, Throwable t) {
                Log.d(TAG, "fail!");
                message.setValue(null);
            }
        });
        return message;
    }
}

3. viewmodel

the method queryRepo is to request login service using phoneNum and password. And it will be used when user click the login button.

public class LoginViewModel extends ViewModel {
    private static final String TAG = "UserProfileViewModel";

    private LoginRepository mLoginRepository;

    private MutableLiveData<JsonObject> message = new MutableLiveData<>();

    public void queryRepo(String phoneNum, String password) {
        this.message = mLoginRepository.getLoginMessage(phoneNum, password);
    }

    public LiveData<JsonObject> getMessage() {
        return message;
    }
}

4. Activity login

public class LoginActivity extends AppCompatActivity implements View.OnClickListener {
    private static final String TAG = "LoginActivity";

    private TextView mForgetPswTv, mRegisterTv;
    private EditText mPhoneEdt, mPasswordEdt;
    private QMUIRoundButton mLoginBtn;
    private ProgressBar mProgressBar;

    private LoginViewModel mLoginViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        getSupportActionBar().hide();
        setContentView(R.layout.activity_login);
        initView();
        bindOperation();
        mLoginViewModel = new ViewModelProvider(this).get(LoginViewModel.class);
        mLoginViewModel.getMessage().observe(this, new Observer<JsonObject>() {
            @Override
            public void onChanged(JsonObject jsonObject) {
                if (jsonObject != null) {
                    mProgressBar.setVisibility(View.GONE);
                    mPasswordEdt.setText(jsonObject.toString());
                } else Log.d(TAG, "null");
            }
        });


    }


    private void initView() {
        mProgressBar = (ProgressBar) findViewById(R.id.progress_circular_movie_article);
        mForgetPswTv = findViewById(R.id.forget_psw_tv);//忘记密码
        mRegisterTv = findViewById(R.id.register_tv);//立即注册
        mLoginBtn = findViewById(R.id.login_btn);
        mPhoneEdt = findViewById(R.id.phone_edt);
        mPasswordEdt = findViewById(R.id.password_edt);
    }


    private void bindOperation() {
        mForgetPswTv.setOnClickListener(LoginActivity.this);
        mRegisterTv.setOnClickListener(LoginActivity.this);
        mLoginBtn.setOnClickListener(v -> {
            mLoginViewModel.queryRepo(mPhoneEdt.getText().toString(), mPasswordEdt.getText().toString());
        });
    }


}

I think it's clear, but I really don't know why it doesn't work, When I touch the login button, this.message.getValue() will change to null. is there something important that I missed? actually, if I don't initialize the message, the first time I call queryRepo is fine, but once the message is assigned a value, if I call queryRepo again, message.getValue() will be null.

Answer 1

I finally made it, just as below.

mLoginBtn.setOnClickListener(v -> {
    mLoginViewModel.queryRepo(mPhoneEdt.getText().toString(), mPasswordEdt.getText().toString());
    mLoginViewModel.getMessage().observe(this, new Observer<JsonObject>() {
            @Override
            public void onChanged(JsonObject jsonObject) {
                if (jsonObject != null) {
                    mProgressBar.setVisibility(View.GONE);
                    mPasswordEdt.setText(jsonObject.toString());
                } else Log.d(TAG, "null");
            }
        });
});

Thanks for everybody again!

Answer 2

Try to Observe live data into Button OnClickListener, Like this, and check

 mLoginBtn.setOnClickListener(v -> {
            mLoginViewModel.queryRepo(mPhoneEdt.getText().toString(), mPasswordEdt.getText().toString());

            mLoginViewModel.getMessage().observe(this, new Observer<JsonObject>() {
            @Override
            public void onChanged(JsonObject jsonObject) {
                if (jsonObject != null) {
                    mProgressBar.setVisibility(View.GONE);
                    mPasswordEdt.setText(jsonObject.toString());
                } else Log.d(TAG, "null");
            }
       });
 });