Question

我在从mySQL检索数据后尝试设置TextView的文本时，我的适配器遇到问题， Doinbackground() + jsonParsing成功

当它进入onPostexecute时，我会尝试将价格文本设置为“任何事物”，并在那里显示null pointer exception。

如果我评论price.setText("anything");应用程序将正常运行，我从URL获取2个json对象实例并在我的listview中创建两个对象，但当然没有检索到的数据。

所有TextView s setText()也会发生这种情况。

代码在这里：

     public class Search extends Activity  {
 public static  String IP=Mysynch.IP;
static String url="http://"+IP+":80/senior/getStoreItemtoJson.php";
 String Scatid; 
String Sitemid;
String Suserid;
String Sdescription;
String Sprice;
String Squantity;
String Showmanyorders;
String Sprocessingtime;
String Sdeliverytime;
String Sdateadded;
String Sbrand;
String Ssale;
String Sbrandnew;
String Ssecondhand;
Activity activity;
List<Itemclass> list=new ArrayList<Itemclass>();
TextView  price;


TextView  desc;
TextView  quantity;


 ListView listview;
ViewGroup viewgroup;
Itemclass itemclass;Itemclass currentitem ;

    @Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    System.out.println(url);
    setContentView(R.layout.search);


        (new myAsynctask()).execute();

        System.out.println("Create");
       }



         public class myAsynctask extends AsyncTask<String, Void, Boolean>
      {
protected void onPreExecute()
{
    System.out.println("pre");
}

protected Boolean  doInBackground(final String... args) {
    System.out.println("Enter background");
    //this client handles the download and upload of the info
         DefaultHttpClient httpclient=new DefaultHttpClient(new BasicHttpParams());
         // Here we pass the url 
         HttpPost httppost=new HttpPost(url);
         httppost.setHeader("Content-type","application/json");
         InputStream inputstream=null;
         String result=null;

         try{
        HttpResponse response=httpclient.execute(httppost);  
        HttpEntity entity=response.getEntity();
        inputstream=entity.getContent();
        BufferedReader reader=new BufferedReader(new InputStreamReader(inputstream,"UTF-                 8"),8);
        StringBuilder Sbuilder=new StringBuilder();
        String line=null;
        while((line=reader.readLine())!=null){
            Sbuilder.append(line+'\n');
        }
             result=Sbuilder.toString();


         }

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

         }finally{
             try{if(inputstream !=null )
            inputstream.close();     

             }
             catch(Exception e){
                 e.printStackTrace();
             }
         };
         System.out.println("finish conx + json");

         JSONArray jsonArray;
         try{
             //jibit awal json object ili howi b2albo kil shi
             JSONObject jsonobj=new JSONObject(result); 
           // String s= jsonobj.getString("success");
             //System.out.println(s);
           //String e=  jsonobj.getString("error");
           //System.out.println(e);
           jsonArray=jsonobj.getJSONArray("item");
             //how to get all objects into a json array
            // query array fiya kil el names ta3on el quote object eli jibti fo2
            //create a list
            for(int i=0;i<jsonArray.length();i++){
                JSONObject jsonline=jsonArray.getJSONObject(i);
                Scatid=jsonline.getString("catid");
                Sitemid=jsonline.getString("itemid");
                Suserid=jsonline.getString("userid");
                Sdescription=jsonline.getString("description");
                Sprice=jsonline.getString("price");
                Squantity=jsonline.getString("quantity");
                Showmanyorders=jsonline.getString("howmanyorders");
                Sprocessingtime=jsonline.getString("processingtime");
                Sdeliverytime=jsonline.getString("deliverytime");
                Sdateadded=jsonline.getString("dateadded");
                Sbrand=jsonline.getString("brand");
                Ssale=jsonline.getString("sale");
                Sbrandnew=jsonline.getString("brandnew");
                Ssecondhand=jsonline.getString("secondhand");


            Itemclass item=new Itemclass(Scatid, Sitemid, Suserid, Sdescription, Sprice,      Squantity, Showmanyorders, 
                    Sprocessingtime, Sdeliverytime, Sdateadded, Sbrand, Ssale, Sbrandnew, Ssecondhand);
            list.add(item);
            System.out.println("*******"+Sprice);
            }

         }catch(JSONException e ){
             e.printStackTrace();
         }
         System.out.println("*****************************************");
    return true;

}

protected void onPostExecute(final Boolean success)
{


    System.out.print("enter post");
    if(success){
        System.out.print(" enter initialize list"); 
        listview=(ListView)findViewById(R.id.listView1);
        ArrayAdapter<Itemclass> adapter = new MyListAdapter();

        listview.setAdapter(adapter);
        System.out.print("initialize list");        }
}
    }

              private class MyListAdapter extends ArrayAdapter<Itemclass> {
public MyListAdapter() {
    super(Search.this, R.layout.searchlistitems, list);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    // Make sure we have a view to work with (may have been given null)
    View itemView = convertView;
    if (itemView == null) {


            itemView   =getLayoutInflater().inflate(R.layout.searchlistitems,
           parent, false);


         }

    currentitem = list.get(position);
    price=(TextView)findViewById(R.id.tvSearchprice);
    desc=(TextView)findViewById(R.id.tvsearchDescr);
    quantity=(TextView)findViewById(R.id.tvSearchquantity);

    System.out.println("position===>>>>"+position);
// price.setText("any thing");//<======== my problem is here


    // Fill the view
//ImageView imageView = (ImageView)itemView.findViewById(R.id.item_icon);
//imageView.setImageResource(currentCar.getIconID());





//desc.setText(currentitem.description);

    //      quantity.setText(currentitem.quantity);

           System.out.println("desc===>>>>"+currentitem.description);
    return itemView;
}               
     }


         }

Answer 1

当你用getView方法夸大布局时：

itemView = getLayoutInflater().inflate(R.layout.searchlistitems, parent, false);

您使用此膨胀视图检索您的子视图，如下所示：

price = (TextView) itemView.findViewById(R.id.tvSearchprice); // use itemView
desc = (TextView) itemView.findViewById(R.id.tvsearchDescr);
quantity = (TextView) itemView.findViewById(R.id.tvSearchquantity);

但是，我建议您使用ViewHolder模式为您的适配器提供更好的性能。这是一个很棒的主题：Performance Tips for Android’s ListView和一个简单的教程：Android ViewHolder Pattern Example。它将避免在ListView滚动期间频繁调用findViewById()。

在android中使用布局膨胀时出现空指针异常

1 个答案: