如何在 android NullPointerException 中解析 JSONArray

Question

我想解析另一个传递过来的jsonObject activity

intent.putextra("result", json.toString());

它显示了名称、分支和会话的所有内容。但它在获取数组时显示 NullPointerException。在这里

            mSubList.add(map);

这个数组有 6 行。这是我的代码。请告诉我到底哪里错了。

JSONObject json;
ListView sub_list;

private JSONArray mComments = null;
private ArrayList<HashMap<String, String>> mSubList;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_result_page);

    name = (TextView)findViewById(R.id.name_roll);
    branch= (TextView)findViewById(R.id.branchname);
    session = (TextView)findViewById(R.id.Session);

    sub_list = (ListView)findViewById(R.id.sub_list);



    try {
         json = new JSONObject(getIntent().getStringExtra("result"));

        name.setText(json.getString("REGNO")+" - "+json.getString("STUDENTNAME"));
        branch.setText(json.getString("BRANCHNAME"));
        session.setText(json.getString("SESSIONNAME"));

        mComments = json.getJSONArray("DATA");

        // looping through all subjects according to the json object returned
        for (int i = 0; i < mComments.length(); i++) {
            JSONObject c = mComments.getJSONObject(i);

            // gets the content of each tag
            String code = c.getString("CCODE");
            String subject = c.getString("COURSENAME");
            String passfail = c.getString("PASSFAIL");

            // creating new HashMap
            HashMap<String, String> map = new HashMap<String, String>();

            map.put("CCODE", code);
            map.put("COURSENAME", subject);
            map.put("PASSFAIL", passfail);
            // adding HashList to ArrayList
            mSubList.add(map);
        }

                ListAdapter adapter = new SimpleAdapter(this, mSubList,
                R.layout.singlesubject, new String[] { "CCODE", "COURSENAME",
                "PASSFAIL" }, new int[] { R.id.sub_id, R.id.sub_name,R.id.sub_res });

        sub_list.setAdapter(adapter);
    }catch(Exception e){
        e.printStackTrace();
    }
  }
}

如果我想更改每个列表项背景(R.layout.singlesubject) 如果"PASSFAIl"=P 那么绿色，否则红色。那么我必须做些什么改变呢？

Answer 1

mSubList.add(map);

这行代码失败，因为您在添加地图之前没有初始化数组

您可以使用...初始化它...

mSubList = new ArrayList<Hashmap<String, String>>();

Answer 2

在添加项目之前初始化您的 mSubList

mSubList = new ArrayList<HashMap<String, String>>();

Answer 3

我想你在添加数据之前忘记初始化 mSubList:

mSubList = new ArrayList<HashMap<String, String>>();

如何在 android NullPointerException 中解析 JSONArray

how to parse JSONArray in android NullPointerException

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json