如何在onPostExecute Asynctask中設置列表適配器？

Question

美好的一天大家，

我在這裏有一些問題。我在AsyncTask DoInBackground中進行Web服務調用。

，我想設置列表適配器，但我得到了錯誤

java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference 

現在怎麼設置列表適配器後執行什麼？

我的代碼

protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_profile); 
    progressBar = (ProgressBar)findViewById(R.id.prgLoading); 


    //Initialize the ListView 
    final ListView lvProf = (ListView)findViewById(R.id.lvProfile); 

    //call the asynctask cals and add item to the list. 
    new LoadDataForActivity().execute(); 

    //Set adapter , but i got error here 
    lvProf.setAdapter(new ListProfileAdapter(this,mItems)); 



} 

private class LoadDataForActivity extends AsyncTask<Void, Void, Void> { 
    @Override 
    protected void onPreExecute() { 
     getWindow().setFlags(WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE, 
       WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE); 
     progressBar.setVisibility(View.VISIBLE); 
     progressBar.setIndeterminate(false); 
     progressBar.setClickable(false); 
    } 
    @Override 
    protected Void doInBackground(Void... params) { 

     getAll(); 
     getTotalLeaveBalance(); 
     getMedicalBalance(); 
     return null; 
    } 

    @Override 
    protected void onPostExecute(Void result) { 
    //here is I add the item to my list (mitems) 
     try{ 
      ResponseServiceMedicalBalance = ResponseServiceMedicalBalance.replace("\\\"", "\""); 
      ResponseServiceMedicalBalance = ResponseServiceMedicalBalance.substring(1, ResponseServiceMedicalBalance.length() - 1); 

      JSONParser jsonParser = new JSONParser(); 
      JSONObject jsonObject = (JSONObject) jsonParser.parse(ResponseServiceMedicalBalance); 
      String Status = jsonObject.get("Status").toString(); 

      if (Status == "true") { 
       // JSONArray structure = (JSONArray) jsonObject.get("DataList"); 
       String dataku = jsonObject.get("DataList").toString(); 
       mItems = new ArrayList<ListProfileItem>(); 
       try { 
        dataku = ANGGACRYYPT.decrypt(Enc_Pass, dataku); 
       }catch (GeneralSecurityException e){ 
        //handle error - could be due to incorrect password or tampered encryptedMsg 
       } 

       JSONParser parser = new JSONParser(); 
       JSONArray structure = (JSONArray) parser.parse(dataku); 
       for (int i = 0; i < structure.size(); i++) { 
        JSONObject data = (JSONObject) structure.get(i); 
        item = new ListProfileItem(); 
        item.claimpostname = data.get("claim_post_name").toString(); 
        String claimamount = data.get("max_limit_per_year").toString(); 
        if (claimamount!=("0.0")) 
        { 
         Double amount = Double.parseDouble(claimamount); 
         DecimalFormat formatter = new DecimalFormat("#,###.00"); 
         String AmountFormatted = formatter.format(amount); 
         item.claimpostamount = AmountFormatted; 
        } 
        else 
        { 
         item.claimpostamount = data.get("max_limit_per_year").toString(); 
        } 
        mItems.add(item); 
       } 
       // initialize and set the list adapter 

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

} 

Answer 1

移動它的onCreate到onPostExecute（） 定義適配器的實例作爲全局變量，然後在doInBackground（）調用& setAdapter onPostExec添加項目。

//Set adapter , but i got error here >> move it to onPostExecute 
    lvProf.setAdapter(new ListProfileAdapter(this,mItems)); 

Answer 2

有解決這個，一個快速的幾種方式和最骯髒的是：

更改AsyncTaskActivity像這樣：

private class LoadDataForActivity extends AsyncTask<Void, Void, Void> { 


    private ListView listView; 

    private Context context; 

    public LoadDataForActivity(ListView listView,Context context){ 
    this. listView = listView; 
    this.context = context; 
    } 

    @Override 
    protected void onPreExecute() { 
     getWindow().setFlags(WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE, 
       WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE); 
     progressBar.setVisibility(View.VISIBLE); 
     progressBar.setIndeterminate(false); 
     progressBar.setClickable(false); 
    } 
    @Override 
    protected Void doInBackground(Void... params) { 

     getAll(); 
     getTotalLeaveBalance(); 
     getMedicalBalance(); 
     return null; 
    } 

    @Override 
    protected void onPostExecute(Void result) { 
    //here is I add the item to my list (mitems) 
     try{ 
      ResponseServiceMedicalBalance = ResponseServiceMedicalBalance.replace("\\\"", "\""); 
      ResponseServiceMedicalBalance = ResponseServiceMedicalBalance.substring(1, ResponseServiceMedicalBalance.length() - 1); 

      JSONParser jsonParser = new JSONParser(); 
      JSONObject jsonObject = (JSONObject) jsonParser.parse(ResponseServiceMedicalBalance); 
      String Status = jsonObject.get("Status").toString(); 

      if (Status == "true") { 
       // JSONArray structure = (JSONArray) jsonObject.get("DataList"); 
       String dataku = jsonObject.get("DataList").toString(); 
       mItems = new ArrayList<ListProfileItem>(); 
       try { 
        dataku = ANGGACRYYPT.decrypt(Enc_Pass, dataku); 
       }catch (GeneralSecurityException e){ 
        //handle error - could be due to incorrect password or tampered encryptedMsg 
       } 

       JSONParser parser = new JSONParser(); 
       JSONArray structure = (JSONArray) parser.parse(dataku); 
       for (int i = 0; i < structure.size(); i++) { 
        JSONObject data = (JSONObject) structure.get(i); 
        item = new ListProfileItem(); 
        item.claimpostname = data.get("claim_post_name").toString(); 
        String claimamount = data.get("max_limit_per_year").toString(); 
        if (claimamount!=("0.0")) 
        { 
         Double amount = Double.parseDouble(claimamount); 
         DecimalFormat formatter = new DecimalFormat("#,###.00"); 
         String AmountFormatted = formatter.format(amount); 
         item.claimpostamount = AmountFormatted; 
        } 
        else 
        { 
         item.claimpostamount = data.get("max_limit_per_year").toString(); 
        } 
        mItems.add(item); 
       } 

    listView.setAdapter(new ListProfileAdapter(context,mItems)); 


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

而且你可以調用的AsyncTask是這樣的：

new LoadDataForActivity(listView,this).execute(); 

Answer 3

初始化模塊爲

mItems = new ArrayList<>(); 

創建對象ListProfileAdapter

ListProfileAdapter adapter = new ListProfileAdapter(this,mItems); 
lvProf.setAdapter(adapter); 

添加項mItems

mItems.add(item); 

後的所有項目添加到列表通知適配器

adapter.notifyDataSetChanged(); 

Answer 4

我覺得下面的行應在設置您的適配器之前，

讓實例變量，

ListProfileAdapter adapter; 

而不是把在的AsyncTask。在完成的AsyncTask在onPostExecute還需要磨合，

adapter.notifyDatasetChanged();