Android 改装错误：java.lang.NullPointerException:尝试对空对象引用调用虚拟方法

我正在尝试创建一个应用程序，允许用户注册和注册帐户

这个问题我已经被问过好几次了，但我不能用同样的解决方案来解决我的问题

我收到错误信息

/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.app, PID: 12181
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String okhttp3.ResponseBody.string()' on a null object reference
        at com.example.app.MainActivity$1.onResponse(MainActivity.java:75)
        at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:70)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
I/Process: Sending signal. PID: 12181 SIG: 9
Process 12181 terminated.

我的改装客户是这个

public class RetrofitClient {

    private static final String BASE_URL = "http://123.456.789.101:5000/api/";
    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);
    }
}

public interface Api {
    @FormUrlEncoded
    @POST("/users/")
    Call<ResponseBody> createUser(
            @Field("email") String email,
            @Field("password") String password

    );
}

Call<ResponseBody> call = RetrofitClient
                .getInstance()
                .getApi()
                .createUser(email, password);

        call.enqueue(new Callback<ResponseBody>() {
            @Override
            public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
                try {
                    String s = response.body().string();
                    Toast.makeText(MainActivity.this, s, Toast.LENGTH_LONG).show();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void onFailure(Call<ResponseBody> call, Throwable t) {
                Toast.makeText(MainActivity.this, t.getMessage(), Toast.LENGTH_LONG).show();

            }
        });

API接口就是这样的

public class RetrofitClient {

    private static final String BASE_URL = "http://123.456.789.101:5000/api/";
    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);
    }
}

public interface Api {
    @FormUrlEncoded
    @POST("/users/")
    Call<ResponseBody> createUser(
            @Field("email") String email,
            @Field("password") String password

    );
}

Call<ResponseBody> call = RetrofitClient
                .getInstance()
                .getApi()
                .createUser(email, password);

        call.enqueue(new Callback<ResponseBody>() {
            @Override
            public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
                try {
                    String s = response.body().string();
                    Toast.makeText(MainActivity.this, s, Toast.LENGTH_LONG).show();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void onFailure(Call<ResponseBody> call, Throwable t) {
                Toast.makeText(MainActivity.this, t.getMessage(), Toast.LENGTH_LONG).show();

            }
        });

公共接口Api{
@FormUrlEncoded
@POST（“/users/”）
调用createUser(
@字段（“电子邮件”）字符串电子邮件，
@字段（“密码”）字符串密码
);
}

而主要活动就是这个

public class RetrofitClient {

    private static final String BASE_URL = "http://123.456.789.101:5000/api/";
    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);
    }
}

public interface Api {
    @FormUrlEncoded
    @POST("/users/")
    Call<ResponseBody> createUser(
            @Field("email") String email,
            @Field("password") String password

    );
}

Call<ResponseBody> call = RetrofitClient
                .getInstance()
                .getApi()
                .createUser(email, password);

        call.enqueue(new Callback<ResponseBody>() {
            @Override
            public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
                try {
                    String s = response.body().string();
                    Toast.makeText(MainActivity.this, s, Toast.LENGTH_LONG).show();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void onFailure(Call<ResponseBody> call, Throwable t) {
                Toast.makeText(MainActivity.this, t.getMessage(), Toast.LENGTH_LONG).show();

            }
        });

Call=client
.getInstance（）
.getApi（）
.createUser（电子邮件、密码）；
call.enqueue（新回调（）{
@凌驾
公共void onResponse（调用、响应）{
试一试{
String s=response.body（）.String（）；
Toast.makeText（MainActivity.this，s，Toast.LENGTH_LONG.show（）；
}捕获（IOE异常）{
e、 printStackTrace（）；
}
}
@凌驾
失败时公共无效（调用调用，可丢弃的t）{
Toast.makeText（MainActivity.this，t.getMessage（），Toast.LENGTH_LONG.show（）；
}
});

---

响应为空，因此我假设这是客户端的问题，但不确定如何修复

可能您的响应为空，请先检查它

if(response.body() != null) {
        String s = response.body().string();
    }

---

这回答了你的问题吗？不抱歉，我无法将该修复应用于我自己的情况您的问题在这里“String s=response.body（）.String（）；“first validate this part”response.body（）“如果不为null，则继续，如果（response.body（）！=null）或检查是否已经存在类似if（！response.body（）.isNull）的内容