动态刷新后如何在listview中保留旧项目？

Question

我有listview，其子项来自服务器。我已经设法在每个平滑滚动后获得10个列表项但我的问题是在添加新项目之后，之前的数据被清除。我也想要旧儿童用品。我也使用了MyListAdapter().notifyDataSetChanged();但没有获得理想的结果。 伙计们请帮帮我。先感谢您。   这是我的代码片段：

Get_list.java：

private class getbride extends AsyncTask<String, String, String>{
    ProgressDialog pDialog;
     @Override
     protected void onPreExecute(){
        pDialog = new ProgressDialog(User_list.this);
        pDialog.setMessage("Loading...");
        pDialog.show();
     }                      
    @Override
    protected String doInBackground(String... params) {
        // TODO Auto-generated method stub

        try{
            String link = "http://Webservice.php";          

            HttpClient client = new DefaultHttpClient();
            HttpPost request = new HttpPost();
            request.setURI(new URI(link));

            List<NameValuePair> postParameters = new ArrayList<NameValuePair>();

            String lazy=String.valueOf(lcnt);
            postParameters.add(new BasicNameValuePair("lazy_cnt", lazy));

            UrlEncodedFormEntity form = new UrlEncodedFormEntity(postParameters);
            request.setEntity(form);

            HttpResponse response = client.execute(request); 
            HttpEntity entity = response.getEntity();

            result=EntityUtils.toString(entity);
            result1 = result;
            System.out.println("Result: "+result);

            SharedPreferences pref1 = getSharedPreferences("ActivityPREF", Context.MODE_PRIVATE);
            Editor ed = pref1.edit();
            ed.putString("search_res", result);
            ed.commit();

        }catch (URISyntaxException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;            
    }
     @Override
        protected void onPostExecute(String result) {
         pDialog.dismiss();
        lv=(ListView)findViewById(R.id.listreq15);  

        try {     
              if(User_list.result!=null){
                jArray=new JSONArray(User_list.result);  

                prgmNameList =new ArrayList<String>();
                prgmImages=new ArrayList<String>();
                if(jArray.length()>0)
                {
                    for(int j=0;j<jArray.length();j++){
                        prgmNameList.add(new JSONObject(jArray.getString(j)).get("name")+"");   
                        prgmImages.add(new JSONObject(jArray.getString(j)).get("education")+"");
                       }        
                    System.out.println("#########"+prgmNameList);
        CustomAdapter cadapt = new CustomAdapter(c, prgmNameList, prgmImages);

                    flag_loading=false; 

                    lv.setAdapter(cadapt);
                    lv.invalidateViews();
                    cadapt.notifyDataSetChanged();

                    int count=lv.getAdapter().getCount();
                    String cnt_bride=String.valueOf(count);
                    TextView list_cnt=(TextView)findViewById(R.id.cnt);
                    list_cnt.setText(cnt_bride);

                    lv.setOnScrollListener(new OnScrollListener() {
                        @Override
                        public void onScroll(AbsListView view, int firstVisibleItem,
                                int visibleItemCount, int totalItemCount) {
                            // TODO Auto-generated method stub
                            if(firstVisibleItem+visibleItemCount == totalItemCount && totalItemCount!=0)
                            {
                                if(flag_loading == false)
                                {
                                    flag_loading = true;
                                    new getbride().execute("param1","param2","param3");
                                    lcnt++;

                                    int count=lv.getAdapter().getCount();
                                    String cnt_bride=String.valueOf(count);
                                    TextView list_cnt=(TextView)findViewById(R.id.cnt);
                                    list_cnt.setText(cnt_bride);
                                }
                            }                               
                        }
                        @Override
                        public void onScrollStateChanged(AbsListView arg0,
                                int arg1) {
                            // TODO Auto-generated method stub

                        }
                    });
                }
              }else{
                  Toast.makeText(getApplicationContext(),"No internet connection...", Toast.LENGTH_SHORT).show();
              }
            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
}

Activity.java：

public class User_list extends Activity {
ListView lv;
JSONArray jArray;
Context c;
public static int cnt,lcnt;
public static String result,result1,partial,u_id,result2,edu,f_name;
int age,ht;
boolean flag_loading;
public static List<String> prgmImages;
public static List<String> prgmNameList;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_user_list);

    Intent i = getIntent();
    String call=i.getStringExtra("call_for");
    if(call==null){
        try {
            search();
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    else if(call.equalsIgnoreCase("br")){
    new getbride().execute("param1","param2","param3");
    lcnt=0;
    }

    else{
        new getgroom().execute("param1","param2","param3");
        lcnt=0;
    }
    c=this;  }

Answer 1

声明并设置CustomAdapter，并初始化ArrayLists中的Activity：

public class User_list extends Activity {
ListView lv;
JSONArray jArray;
Context c;
public static int cnt,lcnt;
public static String result,result1,partial,u_id,result2,edu,f_name;
int age,ht;
boolean flag_loading;
public static List<String> prgmImages;
public static List<String> prgmNameList;
CustomAdapter cadapt; //Added declaration here
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_user_list);


     lv=(ListView)findViewById(R.id.listreq15); //added
     prgmNameList =new ArrayList<String>(); //added
     prgmImages=new ArrayList<String>(); //added
     cadapt = new CustomAdapter(c, prgmNameList, prgmImages); //initialize this here
     lv.setAdapter(cadapt); //added


    Intent i = getIntent();
    String call=i.getStringExtra("call_for");
    if(call==null){
        try {
            search();
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    else if(call.equalsIgnoreCase("br")){
    new getbride().execute("param1","param2","param3");
    lcnt=0;
    }

    else{
        new getgroom().execute("param1","param2","param3");
        lcnt=0;
    }
    c=this;
}

然后在您的AsyncTask中，只需在数据集中添加新值后调用notifyDataSetChanged()：

       @Override
        protected void onPostExecute(String result) {
         pDialog.dismiss();
        //lv=(ListView)findViewById(R.id.listreq15);  //remove

        try {     
              if(User_list.result!=null){
                jArray=new JSONArray(User_list.result);  

                //prgmNameList =new ArrayList<String>(); //remove
                //prgmImages=new ArrayList<String>(); //remove
                if(jArray.length()>0)
                {
                    for(int j=0;j<jArray.length();j++){
                        prgmNameList.add(new JSONObject(jArray.getString(j)).get("name")+"");   
                        prgmImages.add(new JSONObject(jArray.getString(j)).get("education")+"");
                       }        
                    System.out.println("#########"+prgmNameList);
                   //CustomAdapter cadapt = new CustomAdapter(c, prgmNameList, prgmImages); //remove

                    flag_loading=false; 

                    //lv.setAdapter(cadapt); //remove
                    //lv.invalidateViews(); //don't think this is needed
                    cadapt.notifyDataSetChanged(); //This is needed!

                    int count=lv.getAdapter().getCount();
                    String cnt_bride=String.valueOf(count);
                    TextView list_cnt=(TextView)findViewById(R.id.cnt);
                    list_cnt.setText(cnt_bride);

                    lv.setOnScrollListener(new OnScrollListener() {
                        @Override
                        public void onScroll(AbsListView view, int firstVisibleItem,
                                int visibleItemCount, int totalItemCount) {
                            // TODO Auto-generated method stub
                            if(firstVisibleItem+visibleItemCount == totalItemCount && totalItemCount!=0)
                            {
                                if(flag_loading == false)
                                {
                                    flag_loading = true;
                                    new getbride().execute("param1","param2","param3");
                                    lcnt++;

                                    int count=lv.getAdapter().getCount();
                                    String cnt_bride=String.valueOf(count);
                                    TextView list_cnt=(TextView)findViewById(R.id.cnt);
                                    list_cnt.setText(cnt_bride);
                                }
                            }                               
                        }
                        @Override
                        public void onScrollStateChanged(AbsListView arg0,
                                int arg1) {
                            // TODO Auto-generated method stub

                        }
                    });
                }
              }else{
                  Toast.makeText(getApplicationContext(),"No internet connection...", Toast.LENGTH_SHORT).show();
              }
            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

请注意，我不认为此处需要调用invalidateViews()。 请参阅此帖子：Is there any difference between `ListView.invalidateViews()` and 'Adapter.notifyDataSetChanged()'?