如何在 pojoclass 的幫助下將 JSon 數組轉換為 Arraylist？

Question

我無法從我的代碼中得到任何結果。請為我的問題提出解決方案，這是我的代碼，並提前致謝

代碼：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);
    }
    } 
    }

有時也會收到此錯誤：

{"status":{"message":"已超過每日 30000 積分的演示限制。請使用應用程序專用帳戶。請勿將演示帳戶用於您的應用程序。","value":18}}

請告訴我這是什么錯誤

Answer 1

我仍然不知道你為什么在這里使用這個 pojo 概念。

無論如何，我只能建議你在課堂上添加一些 getter/setter。 喜歡

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;
    }


    }

它將幫助您從 JSON 字符串設置和獲取特定數據。

就像是：

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

當你想設置它時::就去做

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

Answer 2

我想你應該檢查這個庫Ion Library 。 它將幫助您異步獲取 JSON 並輕松將其轉換為 POJO 的ArrayList 。

Answer 3

List<PojoClass> pojoClassList;

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

建議你閱讀 Gson 或 Jakson 庫。

Answer 4

將您的視圖持有者模式更改為實現，如下所示。 並且還將 Adapter 的構造函數更改為如下所示的任一實現。

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;

}

在初始化適配器時，根據使用的構造函數執行以下操作。

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

基於新評論的更新
首先是錯誤
1）我觀察到您正在做的一件事是啟動 asynctask 並將適配器設置為列表，而在 onCreate 方法中不獲取或不獲取數據保證，因此您的列表可能為空……您可以這樣做，但是您需要更新適配器中的列表並通知適配器更改的數據集
2）其次，我在您的代碼中觀察到許多列表對象，這有點令人困惑。此外，您還使用了很多靜態的東西...原因我不知道； 但我覺得這是多余的。 像GET(String url) [---它應該被命名為 get(String url)]和convertInputStreamToString(InputStream inputStream)可以在 HttpAsyncTask bcoz 中創建，它僅供該線程使用。
3）你也沒有使用任何東西來表明數據正在從服務器加載

如前所述，我將在適配器更改中添加更多更改。
1）為ListView制作實例變量如下，並在onCreate方法中更改也為setAdapter創建方法

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 你需要調用這個 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) 在您的應用程序中使用ProgressBar view來通知用戶加載正在進行中。 您可以使其可見並在 PreExecute 中啟動並在 PostExecute 中停止和可見性消失