android - 从 Assets 中解析 RecyclerView 中的 JSONArray

Question

我在将 JSON 数据解析到 recyclerview 时遇到了麻烦，当它有数据时试图解析它时抛出 NullPoilnetException 就像 JSONArray 是空的

在recyclerview中显示的Activity解析了里面的数据:

import android.content.Context;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

import org.json.JSONArray;
import org.json.JSONObject;

import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Type;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;


import butterknife.BindView;
import butterknife.ButterKnife;

public class JSONSearchActivity extends AppCompatActivity {
    String TAG = JSONSearchActivity.class.getSimpleName();
    private ArrayList<JSONSearchItem> listContentArr = new ArrayList<>();
    JSONSearchItem item = new JSONSearchItem();
    JSONSearchItemAdapter adapter;

    @BindView(R.id.jsonRecycler) RecyclerView recyclerView;

    Context context;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.search_activity);
        ButterKnife.bind(this);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        adapter = new JSONSearchItemAdapter(listContentArr);
        setJSONItems();
    }
     private void setJSONItems()  {
            try {
                JSONObject jsonObject = new JSONObject(loadJsonEvent("asset1.json"));
                JSONArray message = jsonObject.getJSONArray("Station");

                for (int i = 0; i <= message.length(); i++) {
                    JSONObject temp = message.getJSONObject(i);
                   item.setStationNAme(temp.getString("Name"));
                    item.setStationLine(temp.getString("Line"));
                    listContentArr.add(item);
                    adapter.notifyDataSetChanged();
                    adapter.setListContent(listContentArr);
                    recyclerView.setAdapter(adapter);
                }
        } catch (Exception ex) {
            Log.e(TAG, ex.getMessage());
        }

        }

        //load JSON from Assets
        public String loadJsonEvent(String jsonName) {
            String json = null;
            try {
                InputStream inputStream = getApplicationContext().getAssets().open(jsonName);
                int size = inputStream.available();
                byte[] buffer = new byte[size];
                inputStream.read(buffer);
                inputStream.close();
                json = new String(buffer, StandardCharsets.UTF_8);
            } catch (IOException e) {
                e.printStackTrace();
            }
            return json;
        }
    }

JSON 文件。我用了this分析 json 文件的网站，它显示它有 1 个对象，其中包含项目的“station”数组。所以它不为空

        {
          "Station": [
            {
              "Name": "Station1",
              "Line": "Line1"
            },
            {
              "Name": "Station2",
              "Line": "Line3"
    ....
            }
          ]
        }

正如我之前所说，当应用程序尝试启动时，它会因 NullPoilnetException 和下一个日志而崩溃

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
        at 

    com.appexample.JSONSearchItemAdapter.onBindViewHolder(JSONSearchItemAdapter.java:38)
            at com.appexample.JSONSearchItemAdapter.onBindViewHolder(JSONSearchItemAdapter.java:11)
            at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6781)
            at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6823)
            at android.support.v7.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:5752)
            at android.support.v7.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6019)
            at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5858)
            at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5854)
            at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2230)
            at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1557)
            at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1517)
            at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:612)
            at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3924)
            at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:3336)
            at android.view.View.measure(View.java:19857)

...

我的 RecyclerViewAdapter 名为 JSONSearchItemAdapter :

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.util.ArrayList;

public class JSONSearchItemAdapter extends RecyclerView.Adapter<JSONSearchItemAdapter.MyViewHolder> {
    //Creating an arraylist of POJO objects
    private ArrayList<JSONSearchItem> pad_list;
    View view;
    MyViewHolder holder;
    private Context mcontext;

    public JSONSearchItemAdapter(ArrayList<JSONSearchItem> data){
        this.pad_list = data;
    }
    //This method inflates view present in the RecyclerView
    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.search_activity, parent, false);
        holder = new MyViewHolder(view);
        return holder;
    }

    //Binding the data using get() method of POJO object
    @Override
    public void onBindViewHolder(final MyViewHolder holder, int position) {
        final JSONSearchItem list_items = pad_list.get(position);
        holder.stationName.setText(list_items.getNameStation());//logs show nullpointer error happens here
        holder.lineName.setText(list_items.getStationLine());
    }

    //Setting the arraylist
    public void setListContent(ArrayList <JSONSearchItem> pad_list) {
        this.pad_list = pad_list;
    }

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

    //View holder class, where all view components are defined
    class MyViewHolder extends RecyclerView.ViewHolder {
        TextView stationName, lineName;

        public MyViewHolder(View itemView) {
            super(itemView);
            stationName = itemView.findViewById(R.id.stationView);
            lineName = itemView.findViewById(R.id.lineView);
        }
    }

}

和POJO

public class JSONSearchItem {

    @SerializedName("Line")
    private String stationLine;
    @SerializedName("Name")
    private String nameStation;

    public JSONSearchItem() {

    }

    public String getStationLine() {
        return stationLine;
    }

    public void setStationLine(String stationLine) {
        this.stationLine = stationLine;
    }

    public String getNameStation() {
        return nameStation;
    }

    public void setNameStation(String nameStation) {
        this.nameStation = nameStation;
    }
}

我尝试了另一种结合使用 JSON 和 GSOn 的方法，但它也没有奏效

JSONObject jsonObject = new JSONObject(loadJsonEvent("asset1.json"));
            JSONArray message = jsonObject.getJSONArray("Station");
            Gson gson =new Gson();
            for (int i = 0; i <= message.length(); i++) {
                JSONObject temp =message.getJSONObject(i);
                item = gson.fromJson(temp.toString(), JSONSearchItem.class);
                listContentArr.add(item);
                adapter.notifyDataSetChanged();
                adapter.setListContent(listContentArr);
                recyclerView.setAdapter(adapter);
            }

所以我有一个问题，我的解析代码方法有什么问题，我该如何解决这个问题？提前致谢!

更新:由此引起的错误:我为 View 膨胀设置了与 Activity 相同的布局，当它必须是单个项目所在的布局时

 view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.search_activity, parent, false);

Answer 1

这里指出了主要问题:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

您的 View holder.stationName 具有空值，这是因为您的 search_activity.xml 中不存在 ID 为 stationView 的 View > 布局。