如何在 pojoclass 的帮助下将 JSon 数组转换为 Arraylist？

Question

我无法从我的代码中得到任何结果。请为我的问题提出解决方案，这是我的代码，并提前致谢

代码：Activity.main

 public class MainActivity extends Activity {

 ArrayList<detail> country =  new ArrayList<detail>();

 class detail{
    public String toponymName;
    public String countrycode;
    public int population;
    public String wikipedia;
    }

   Adapter ad = null;
   static ArrayList<string> resultrow;

   protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    new HttpAsyncTask().execute("http://api.geonames.org/citiesJSON?        north=44.1&south=-9.9&east=-22.4&west=55.2&lang=de&username=demo");

    ListView mylistview = (ListView)findViewById(R.id.mylistview);
    ad = new Adapter();
    mylistview.setAdapter(ad);

    }
    public static String GET(String url){
    InputStream inputStream = null;
    String result = "";
    try {
         HttpClient httpclient = new DefaultHttpClient();
         HttpResponse httpResponse = httpclient.execute(new HttpGet(url));
         inputStream = httpResponse.getEntity().getContent();
         if(inputStream != null)
            result = convertInputStreamToString(inputStream);
        else
            result = "Did not work!";

    } catch (Exception e) {
        Log.d("InputStream", e.getLocalizedMessage());}
         return result;
    }

    private static String convertInputStreamToString(InputStream inputStream) throws IOException{
    BufferedReader bufferedReader = new BufferedReader( new InputStreamReader(inputStream));
    String line = "";
    String result = "";
    while((line = bufferedReader.readLine()) != null){
        Log.e("Line",line);
         result += line;
    }
     inputStream.close();
    return result;
    }

    private class HttpAsyncTask extends AsyncTask<String, Void, String> {
    @Override
    protected String doInBackground(String... urls) {

        return GET(urls[0]);
    }
    @Override
    protected void onPostExecute(String result) {
        Toast.makeText(getBaseContext(), "Received!", Toast.LENGTH_LONG).show();
        String strJson = result;

        try {
           JSONObject  jsonRootObject = new JSONObject(strJson);
           JSONArray jsonArray = jsonRootObject.optJSONArray("geonames");
           for(int i=0; i < jsonArray.length(); i++){
               JSONObject jsonObject = jsonArray.getJSONObject(i);
               detail resultrow = new detail();
               resultrow.toponymName =jsonObject.getString("toponymName");
               resultrow.countrycode =jsonObject.getString("countrycode");
               resultrow.wikipedia =jsonObject.getString("wikipedia");
               resultrow.population =jsonObject.getInt("population");
               country.add(resultrow);
       }

        }
           catch (JSONException e) {e.printStackTrace();}   
    } 

    }
    class Adapter extends ArrayAdapter<detail>{
    Adapter(){
                  super(MainActivity.this,android.R.layout.simple_list_item_1,country);
    }
    public View getview(int position,View convertview,ViewGroup parent){
        viewHolder holder;

    if(convertview==null){
        LayoutInflater inflater = getLayoutInflater(); 
        convertview=inflater.inflate(R.layout.row, null); 
        holder = new viewHolder(convertview);
        convertview.setTag(holder);
    }
    else{
        holder=(viewHolder)convertview.getTag();
    }
    holder.populateFrom(country.get(position));
    return convertview;
    }
    }
    class viewHolder{
    public TextView toponymName=null;
    public TextView countrycode=null;
    public TextView wikipedia=null;
    public TextView population=null;

    viewHolder(View row){
        toponymName =(TextView)row.findViewById(R.id.toponymName);
        countrycode =(TextView)row.findViewById(R.id.countrycode);  
        wikipedia =(TextView)row.findViewById(R.id.wikipedia);  
        population =(TextView)row.findViewById(R.id.population);    
        }

      //not able to populate this block 
       void populateFrom(detail r){
        toponymName.setText(r.toponymName);
        countrycode.setText(r.countrycode);
        wikipedia.setText(r.wikipedia);
        population.setText(r.population);
    }
    } 
    }

有时也会收到此错误：

{"status":{"message":"已超过每日 30000 积分的演示限制。请使用应用程序专用帐户。请勿将演示帐户用于您的应用程序。","value":18}}

请告诉我这是什么错误

Answer 1

我仍然不知道你为什么在这里使用这个 pojo 概念。

无论如何，我只能建议你在课堂上添加一些 getter/setter。 喜欢

class detail{
    public String toponymName;
    public String countrycode;
    public int population;
    public String wikipedia;
    public String getToponymName() {
        return toponymName;
    }
    public void setToponymName(String toponymName) {
        this.toponymName = toponymName;
    }
    public String getCountrycode() {
        return countrycode;
    }
    public void setCountrycode(String countrycode) {
        this.countrycode = countrycode;
    }
    public int getPopulation() {
        return population;
    }
    public void setPopulation(int population) {
        this.population = population;
    }
    public String getWikipedia() {
        return wikipedia;
    }
    public void setWikipedia(String wikipedia) {
        this.wikipedia = wikipedia;
    }


    }

它将帮助您从 JSON 字符串设置和获取特定数据。

就像是：

   JSONObject jsonObject = jsonArray.getJSONObject(i);
           detail resultrow = new detail();
           resultrow.setToponymName(jsonObject.getString("toponymName");
          ..........
          .......
           country.add(resultrow);

当你想设置它时::就去做

toponymName.setText(r.getToponymName());
..................................
..................................

Answer 2

我想你应该检查这个库Ion Library 。 它将帮助您异步获取 JSON 并轻松将其转换为 POJO 的ArrayList 。

Answer 3

List<PojoClass> pojoClassList;

pojoClassList = new ObjectMapper().readValue(jsonString,TypeFactory.collectionType(List.class, Employe.class));

建议你阅读 Gson 或 Jakson 库。

Answer 4

将您的视图持有者模式更改为实现，如下所示。 并且还将 Adapter 的构造函数更改为如下所示的任一实现。

class Adapter extends ArrayAdapter<detail>{
  //below variables are optional
  List<detail> actList;
  Context context;

  Adapter(Context context, Context context, int resource, List<detail> actList){
   super(context,resource,actList);
   //below variables are optional
   this.context  = context;
   this.actList = actList;
  }

  ---OR----

  Adapter(Context context, Context context, int resource){
   super(context,resource);
   //below variables are optional
   this.context  = context;
  }

  public View getview(int position,View convertview,ViewGroup parent){

    ViewHolder holder;
    final detail r = actList.get(position);

    if(convertview==null){
        LayoutInflater inflater = getLayoutInflater(); 
        convertview=inflater.inflate(R.layout.row, null);

        holder = new ViewHolder();
        holder.toponymName =(TextView)convertview.findViewById(R.id.toponymName);
        holder.countrycode =(TextView)convertview.findViewById(R.id.countrycode);  
        holder.wikipedia =(TextView)convertview.findViewById(R.id.wikipedia);  
        holder.population =(TextView)convertview.findViewById(R.id.population);

        convertview.setTag(holder);
    } else {
        holder=(ViewHolder)convertview.getTag();
    }

    if(r!= null) {
     holder.toponymName.setText(r.toponymName);
     holder.countrycode.setText(r.countrycode);
     holder.wikipedia.setText(r.wikipedia);
     holder.population.setText(r.population);
    }

    return convertview;
 }
}

static class ViewHolder{

  TextView toponymName;
  TextView countrycode;
  TextView wikipedia;
  TextView population;

}

在初始化适配器时，根据使用的构造函数执行以下操作。

ad = new Adapter(this, R.layout.row, actlist)
OR
ad = new Adapter(this, R.layout.row)

基于新评论的更新
首先是错误
1）我观察到您正在做的一件事是启动 asynctask 并将适配器设置为列表，而在 onCreate 方法中不获取或不获取数据保证，因此您的列表可能为空……您可以这样做，但是您需要更新适配器中的列表并通知适配器更改的数据集
2）其次，我在您的代码中观察到许多列表对象，这有点令人困惑。此外，您还使用了很多静态的东西...原因我不知道； 但我觉得这是多余的。 像GET(String url) [---它应该被命名为 get(String url)]和convertInputStreamToString(InputStream inputStream)可以在 HttpAsyncTask bcoz 中创建，它仅供该线程使用。
3）你也没有使用任何东西来表明数据正在从服务器加载

如前所述，我将在适配器更改中添加更多更改。
1）为ListView制作实例变量如下，并在onCreate方法中更改也为setAdapter创建方法

Adapter ad = null;
ListView listView;

 protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ListView mylistview = (ListView)findViewById(R.id.mylistview);

    new HttpAsyncTask().execute("http://api.geonames.org/citiesJSON?           north=44.1&south=-9.9&east=-22.4&west=55.2&lang=de&username=demo");
}

public void setListAdapter(){
  if(ad == null){
    ad = new Adapter(this, R.layout.row)
    mylistview.setAdapter(ad);
  } else {
    ad.notifydatasetchanged();
  }
}

然后在 postExecute 你需要调用这个 setListAdapter 方法....

@Override
protected void onPostExecute(String result) {
 //your code
 try{
   //your code
   setListAdapter()
 }catch (JSONException e) {e.printStackTrace();//use log i.e Log.e(TAG,msg)}  
}

2) 在您的应用程序中使用ProgressBar view来通知用户加载正在进行中。 您可以使其可见并在 PreExecute 中启动并在 PostExecute 中停止和可见性消失