Question

我正在使用Retrofit与Android上的REST API通信，但是得到如下所示的NullPointerException。我尝试使用邮递员，该API正常工作，并且我得到登录名正常工作的响应。

错误

进程：com.example.krish.webdemo，PID：3064 java.lang.NullPointerException 在com.example.krish.webdemo.activities.LoginActivity $ 2.onResponse

 Call<LoginResponse> call = RetrofitClient
                .getInstance()
                .getApi()
                .userLogin(email, password);

        call.enqueue(new Callback<LoginResponse>() {
            @Override
            public void onResponse(Call<LoginResponse> call, Response<LoginResponse> response) {
                LoginResponse loginResponse = response.body();
                if (!loginResponse.isError()) {
                    Toast.makeText(LoginActivity.this, loginResponse.getMessage(), Toast.LENGTH_LONG).show();
                } else {
                    Toast.makeText(LoginActivity.this, loginResponse.getMessage(), Toast.LENGTH_LONG).show();
                }
            }

            @Override
            public void onFailure(Call<LoginResponse> call, Throwable t) {

            }
        });
    }

我的登录响应有一个NullPointerException，“。isError（）”为显示空错误

API接口

@FormUrlEncoded
    @POST("userlogin")
    Call<LoginResponse> userLogin(
            @Field("email") String email,
            @Field("password") String password
    );

改造实例

private static final String BASE_URL ="http://192.168.1.38/KrishApi/public/";
    private static RetrofitClient mInstance;
    private Retrofit retrofit;

    private RetrofitClient() {


        retrofit = new Retrofit.Builder()
                .baseUrl(BASE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .build();
    }

    public static synchronized RetrofitClient getInstance() {
        if (mInstance == null) {
            mInstance = new RetrofitClient();
        }
        return mInstance;
    }
    public Api getApi(){
        return retrofit.create(Api.class);
    }

JSON响应

{
    "error": false,
    "message": "Login Successful",
    "user": {
        "id": 3,
        "email": "pandi@gmail.com",
        "name": "pandi",
        "age": "22",
        "college": "sec"
    }
}

POJO类

public class LoginResponse {


    private boolean error;
    private String message;
    private User user;

    public LoginResponse(boolean error, String message, User user) {
        this.error = error;
        this.message = message;
        this.user = user;
    }

    public boolean isError() {
        return error;
    }

    public String getMessage() {
        return message;
    }

    public User getUser() {
        return user;
    }
}

Answer 1

如果响应失败，

public class CorsHandler : DelegatingHandler { const string Origin = "Origin"; const string AccessControlRequestMethod = "Access-Control-Request-Method"; const string AccessControlRequestHeaders = "Access-Control-Request-Headers"; const string AccessControlAllowOrigin = "Access-Control-Allow-Origin"; const string AccessControlAllowMethods = "Access-Control-Allow-Methods"; const string AccessControlAllowHeaders = "Access-Control-Allow-Headers"; protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) { bool isCorsRequest = request.Headers.Contains(Origin); bool isPreflightRequest = request.Method == HttpMethod.Options; if (isCorsRequest) { if (isPreflightRequest) { return Task.Factory.StartNew<HttpResponseMessage>(() => { HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK); response.Headers.Add(AccessControlAllowOrigin, request.Headers.GetValues(Origin).First()); string accessControlRequestMethod = request.Headers.GetValues(AccessControlRequestMethod).FirstOrDefault(); if (accessControlRequestMethod != null) { response.Headers.Add(AccessControlAllowMethods, accessControlRequestMethod); } string requestedHeaders = string.Join(", ", request.Headers.GetValues(AccessControlRequestHeaders)); if (!string.IsNullOrEmpty(requestedHeaders)) { response.Headers.Add(AccessControlAllowHeaders, requestedHeaders); } return response; }, cancellationToken); } else { return base.SendAsync(request, cancellationToken).ContinueWith<HttpResponseMessage>(t => { HttpResponseMessage resp = t.Result; resp.Headers.Add(AccessControlAllowOrigin, request.Headers.GetValues(Origin).First()); return resp; }); } } else { return base.SendAsync(request, cancellationToken); } } }返回null。因此，您必须始终在response.body()方法内检查响应是否成功。

onResponse

Answer 2

"error": false,

当应用程序尝试使用
NullPointerException 具有空值的对象引用。

您应该检查您的响应 isSuccess() 。

/ ** {@code true}，如果{@link #code（）}在[200..300）范围内。 * /
公共布尔isSuccess（）{ 返回rawResponse.isSuccessful（）; }

              if (response.isSuccess()) //isSuccessful()
                {
                   LoginResponse loginResponse = response.body();
                    ////
                }

使用翻新响应的NullPointerException

2 个答案: