Question

我目前正在收到一个NullPointerException错误，该错误是由onResponse（）方法中的getMessage（）调用引起的。 response.enqueue（）代码中需要此onResponse（）方法。出于某种原因想到它什么时候

以下是源代码：

import android.app.Fragment;
import android.app.FragmentTransaction;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.support.design.widget.Snackbar;
import android.support.v7.widget.AppCompatButton;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;

import com.mtb.login.models.ServerRequest;
import com.mtb.login.models.ServerResponse;
import com.mtb.login.models.User;

import java.io.IOException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;

import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSession;
import javax.net.ssl.X509TrustManager;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;


public class LoginFragment extends Fragment implements View.OnClickListener {
    private AppCompatButton btn_login;
    private EditText et_email,et_password;
    private TextView tv_register,tv_reset_password;
    private ProgressBar progress;
    private SharedPreferences pref;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_login,container,false);
        initViews(view);

        return view;
    }

    private void initViews(View view) {
        pref = getActivity().getPreferences(0);

        btn_login = (AppCompatButton)view.findViewById(R.id.btn_login);
        tv_register = (TextView)view.findViewById(R.id.tv_register);
        tv_reset_password = (TextView)view.findViewById(R.id.tv_reset_password);
        et_email = (EditText)view.findViewById(R.id.et_email);
        et_password = (EditText)view.findViewById(R.id.et_password);

        progress = (ProgressBar)view.findViewById(R.id.progress);

        btn_login.setOnClickListener(this);
        tv_register.setOnClickListener(this);
        tv_reset_password.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.tv_register:
                goToRegister();
                break;
            case R.id.btn_login:
                String email = et_email.getText().toString();
                String password = et_password.getText().toString();

                if(!email.isEmpty() && !password.isEmpty()) {

                    progress.setVisibility(View.VISIBLE);
                    loginProcess(email,password);

                } else {

                    Snackbar.make(getView(), "Fields are empty !", Snackbar.LENGTH_LONG).show();
                }
                break;
            case R.id.tv_reset_password:
                goToResetPassword();
                break;
        }
    }
    private void loginProcess(String email,String password) {
        Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(Constants.BASE_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build();

        RequestInterface requestInterface = retrofit.create(RequestInterface.class);

        User user = new User();
        user.setEmail(email);
        user.setPassword(password);
        ServerRequest request = new ServerRequest();
        request.setOperation(Constants.LOGIN_OPERATION);
        request.setUser(user);
        Call<ServerResponse> response = requestInterface.operation(request);

        response.enqueue(new Callback<ServerResponse>() {
            @Override
            public void onResponse(Call<ServerResponse> call, retrofit2.Response<ServerResponse> response) {
                if (!response.isSuccessful()) {
                    ServerResponse resp = response.body();
                    Snackbar.make(getView(), resp.getMessage(), Snackbar.LENGTH_LONG).show();

                    if (resp.getResult().equals(Constants.SUCCESS)) {
                        SharedPreferences.Editor editor = pref.edit();
                        editor.putBoolean(Constants.IS_LOGGED_IN, true);
                        editor.putString(Constants.EMAIL, resp.getUser().getEmail());
                        editor.putString(Constants.NAME, resp.getUser().getName());
                        editor.putString(Constants.UNIQUE_ID, resp.getUser().getUnique_id());
                        editor.apply();
                        goToProfile();
                    }
                    progress.setVisibility(View.INVISIBLE);
                }
            }

            @Override
            public void onFailure(Call<ServerResponse> call, Throwable t) {
                progress.setVisibility(View.INVISIBLE);
                Log.d(Constants.TAG,"failed");
                Snackbar.make(getView(), t.getLocalizedMessage(), Snackbar.LENGTH_LONG).show();
            }
        });
    }
}

以下是我目前得到的错误：

06-21 16:12:42.211  28188-28188/com.mtb.login E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.mtb.login, PID: 28188
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.mtb.login.models.ServerResponse.getMessage()' on a null object reference
        at com.mtb.login.LoginFragment$1.onResponse(LoginFragment.java:114)
        at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:68)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6682)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)

这是发生错误的位置：

Snackbar.make(getView(), resp.getMessage(), Snackbar.LENGTH_LONG).show();

这是导致此NPE的代码的一部分：

resp.getMessage()

为什么此响应返回null？任何帮助将不胜感激。

Answer 1

当响应不成功时，您正在调用getMessage方法。因此数据未正确映射到ServerResponse对象。去掉！来自你的if语句

Android - RetroFit响应返回空（NPE）

1 个答案: