从json响应改造android获取数据时出错

Question

在我的应用程序中，我必须获取已接收消息的列表，这些消息存储在服务器的json响应中。 现在，我为此目的创建了几个类：

1）我的界面：

@Headers({"Content-type: application/json"})
@GET("/v1/message/list")
Call<MessageArray> getInMess(@Header("Authorization") String token, @Query("type") int type, @Query("offset") int offset);

2）一条消息的类：

public class Message {
    private int id;
    private String subject;
    private boolean can_delete;
    @SerializedName("new") //this is because new is a protected keyword. this annotation is for Gson parsing library. Any library has his own annotation
    private int newField;
    private String date;
    private String receiver_name;
    private String sender_name;

    public Message() {
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getSubject() {
        return subject;
    }

    public void setSubject(String subject) {
        this.subject = subject;
    }

    public boolean isCan_delete() {
        return can_delete;
    }

    public void setCan_delete(boolean can_delete) {
        this.can_delete = can_delete;
    }

    public int getNewField() {
        return newField;
    }

    public void setNewField(int newField) {
        this.newField = newField;
    }

    public String getDate() {
        return date;
    }

    public void setDate(String date) {
        this.date = date;
    }

    public String getReceiver_name() {
        return receiver_name;
    }

    public void setReceiver_name(String receiver_name) {
        this.receiver_name = receiver_name;
    }

    public String getSender_name() {
        return sender_name;
    }

    public void setSender_name(String sender_name) {
        this.sender_name = sender_name;
    }
}

3）消息数组：

public class MessageArray {
    private int count;
    private List<Message> messages;
    private String next_url;
    private String previous_url;

    public MessageArray() {
    }

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }

    public List<Message> getMessages() {
        return messages;
    }

    public void setMessages(List<Message> messages) {
        this.messages = messages;
    }

    public String getNext_url() {
        return next_url;
    }

    public void setNext_url(String next_url) {
        this.next_url = next_url;
    }

    public String getPrevious_url() {
        return previous_url;
    }

    public void setPrevious_url(String previous_url) {
        this.previous_url = previous_url;
    }
}

4）回应样本：

HTTP 200
{
    "count": int, # number of messages 
    "messages": [ # array of messages
        {
            "id": int, # message id
            "subject": str, # message subject
            "can_delete": bool, # can it be deleted (True) or not (False)
            "new": int # message already read (0) or not (1)
            "date": str, # date of message in 'd.m.y'. If message was sent today format will be 'H:M'
            "receiver_name": str, # name of receiver if type=1
            "sender_name": str, # name of sender if type=0
        }, ...
    ],
    "next_url": URL,  # url for get next messages, if no more messages value is null
    "previous_url": URL # url for get previous messages, if no more messages value is null
}

我决定使用RecyclerView，因为它比ListView更完美，因此我为其创建了类适配器：

class MessageAdapter extends RecyclerView.Adapter<MessageAdapter.ViewHolder>
{
    private List<Message> messageList;
    private Context ctx;

    public MessageAdapter(List<Message> messageList, Context ctx) {
        this.messageList = messageList;
        this.ctx = ctx;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.list_of_rec_m, viewGroup, false);
        return new ViewHolder(v);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Message message = messageList.get(position);
        holder.subject.setText(message.getSubject());
        holder.from.setText(message.getSender_name());
    }

    @Override
    public int getItemCount() {
        return messageList.size();
    }


    class ViewHolder extends RecyclerView.ViewHolder {
        final TextView from,subject;
        ViewHolder(View v) {
            super(v);
            subject = v.findViewById(R.id.subject);
            from = v.findViewById(R.id.from);

            v.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {

                }
            });
        }
    }
}

但现在我不知道如何初始化此recycleView。 我有这样的片段类：

 @Override
    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_received, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
       /* recyclerView = view.findViewById(R.id.list);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));*/
        received();
    }

    public void received() {
        HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();
        interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
        OkHttpClient client = new OkHttpClient.Builder().addInterceptor(interceptor).build();

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("https://server/")
                .client(client)
                .addConverterFactory(GsonConverterFactory.create())
                .build();

        adapter = null;
        //recyclerView.setAdapter(adapter);
        tok_pref = Objects.requireNonNull(getActivity()).getSharedPreferences(ACCESS_TOKEN,Context.MODE_PRIVATE);


        String access_token = tok_pref.getString(ACCESS_TOKEN,"");
        final APIService mAPIService = retrofit.create(APIService.class);
        mAPIService.getInMess("Bearer " + access_token, 0, 1).enqueue(new Callback<MessageArray>() {

            @Override
            public void onResponse(@NonNull Call<MessageArray> call, @NonNull Response<MessageArray> response) {
                if (response.isSuccessful()) {
                   /* messageArrayList = (ArrayList<Message>) response.body().getMessages();
                    adapter = new MessageAdapter(messageArrayList, getActivity());
                    recyclerView.setAdapter(adapter);*/
                }
            }

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

            }
        });
    }

我的logcat回应样本：

{"count": 3, "next_url": null, "previous_url": null, "messages": [{"new": 0, "sender_name": "Poltava - Amina Al-Shahoud", "attach": false, "subject": "\u0441\u0430\u0432\u0441\u0432\u0430 \u0432\u044b\u043c\u0430\u0432", "id": 2409277, "date": "25.07.18", "can_delete": true}, {"new": 0, "sender_name": "Poltava - Amina Al-Shahoud", "attach": false, "subject": "\u043f\u0440\u0435\u0432\u0435\u0434", "id": 2409276, "date": "25.07.18", "can_delete": true}, {"new": 0, "sender_name": "Poltava - Amina Al-Shahoud", "attach": false, "subject": "AW: Neu registrierte/r Bewerber/in Andrew Horoshko (ID 9533961) in Ihrer Vermittlungsdokumentation", "id": 2407651, "date": "19.07.18", "can_delete": true}]}

我的最后一个错误：

08-03 04:45:26.112 3978-3978/com.example.developer_4.test_login E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.developer_4.test_login, PID: 3978
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference
        at com.example.developer_4.test_login.Tabs.Received.onCreateView(Received.java:46)
        at android.support.v4.app.Fragment.performCreateView(Fragment.java:2425)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1460)
        at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1784)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1852)
        at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:802)
        at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2623)
        at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2410)
        at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2365)
        at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:2242)
        at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:654)
        at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:168)
        at android.support.v4.view.ViewPager.populate(ViewPager.java:1244)
        at android.support.v4.view.ViewPager.populate(ViewPager.java:1092)
        at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1622)
        at android.view.View.measure(View.java:19857)
        at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
        at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
        at android.view.View.measure(View.java:19857)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
        at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:733)
        at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:95)
        at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1536)
        at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:803)
        at android.view.View.measure(View.java:19857)
        at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1121)
        at android.view.View.measure(View.java:19857)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
        at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:143)
        at android.view.View.measure(View.java:19857)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:758)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
        at android.view.View.measure(View.java:19857)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
        at android.view.View.measure(View.java:19857)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:758)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
        at android.view.View.measure(View.java:19857)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
        at com.android.internal.policy.DecorView.onMeasure(DecorView.java:689)
        at android.view.View.measure(View.java:19857)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2275)
        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1366)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1619)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1254)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6337)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:874)
        at android.view.Choreographer.doCallbacks(Choreographer.java:686)
        at android.view.Choreographer.doFrame(Choreographer.java:621)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:860)
        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:6119)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

我希望你能帮助我解决我的问题。 感谢您的良好建议和答案。

Answer 1

删除onViewCreated并在onCreateView添加以下内容

@Override
public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_received, container, false);
recyclerView = (RecyclerView) rootView.findViewById(R.id.list);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));*/
    received();
 return rootView;
}

也尝试为Message添加@SerializedName批注

    public class Message {

@SerializedName("new")
@Expose
private Integer _new;
@SerializedName("sender_name")
@Expose
private String senderName;
@SerializedName("attach")
@Expose
private Boolean attach;
@SerializedName("subject")
@Expose
private String subject;
@SerializedName("id")
@Expose
private Integer id;
@SerializedName("date")
@Expose
private String date;
@SerializedName("can_delete")
@Expose
private Boolean canDelete;

public Integer getNew() {
return _new;
}

public void setNew(Integer _new) {
this._new = _new;
}

public String getSenderName() {
return senderName;
}

public void setSenderName(String senderName) {
this.senderName = senderName;
}

public Boolean getAttach() {
return attach;
}

public void setAttach(Boolean attach) {
this.attach = attach;
}

public String getSubject() {
return subject;
}

public void setSubject(String subject) {
this.subject = subject;
}

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getDate() {
return date;
}

public void setDate(String date) {
this.date = date;
}

public Boolean getCanDelete() {
return canDelete;
}

public void setCanDelete(Boolean canDelete) {
this.canDelete = canDelete;
}

}

对于MessageArray

    public class MessageArray {

@SerializedName("count")
@Expose
private Integer count;
@SerializedName("next_url")
@Expose
private Object nextUrl;
@SerializedName("previous_url")
@Expose
private Object previousUrl;
@SerializedName("messages")
@Expose
private List<Message> messages = null;

public Integer getCount() {
return count;
}

public void setCount(Integer count) {
this.count = count;
}

public Object getNextUrl() {
return nextUrl;
}

public void setNextUrl(Object nextUrl) {
this.nextUrl = nextUrl;
}

public Object getPreviousUrl() {
return previousUrl;
}

public void setPreviousUrl(Object previousUrl) {
this.previousUrl = previousUrl;
}

public List<Message> getMessages() {
return messages;
}

public void setMessages(List<Message> messages) {
this.messages = messages;
}

}