無法在setOnClickListener中執行Asynctask

Question

我在這行有錯誤 - > new GetHttpResponse（this）.execute（）;

它好好嘗試一下有錯誤時，它被放在按鈕

我從http://www.android-examples.com/create-dynamic-listview-using-json-parsing-php-mysql/得到這個代碼，我剛纔添加的按鈕，以便它可以在更新數據庫被刷新外

public class MainActivity extends Activity { 

    ListView listCollege; 
    ProgressBar proCollageList; 
    Button bton; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) 
{ 
    super.onCreate(savedInstanceState); 
    requestWindowFeature(Window.FEATURE_NO_TITLE); 
    setContentView(R.layout.activity_main); 
    bton = (Button) findViewById(R.id.button); 
    listCollege = (ListView)findViewById(R.id.listCollege); 
    proCollageList = (ProgressBar)findViewById(R.id.proCollageList); 
    new GetHttpResponse(this).execute(); 

    bton.setOnClickListener(new OnClickListener() { 
     @Override 
     public void onClick(View view) { 
      Toast.makeText(MainActivity.this, "List is refreshed", Toast.LENGTH_SHORT).show(); 
      new GetHttpResponse(this).execute(); 
     }}); 
} 



    private class GetHttpResponse extends AsyncTask<Void, Void, Void> 
    { 
     private Context context; 
     String result; 
     List<benedict.com.listviewpractice.cources> collegeList; 
     public GetHttpResponse(Context context) 
     { 
      this.context = context; 
     } 

     @Override 
     protected void onPreExecute() 
     { 
      super.onPreExecute(); 
     } 

     @Override 
     protected Void doInBackground(Void... arg0) 
     { 
      HttpService httpService = new HttpService("http://10.0.2.2/courses.php"); 
      try 
      { 
       httpService.ExecutePostRequest(); 

       if(httpService.getResponseCode() == 200) 
       { 
        result = httpService.getResponse(); 
        Log.d("Result", result); 
        if(result != null) 
        { 
         JSONArray jsonArray = null; 
         try { 
          jsonArray = new JSONArray(result); 

          JSONObject object; 
          JSONArray array; 
          benedict.com.listviewpractice.cources college; 
          collegeList = new ArrayList<benedict.com.listviewpractice.cources>(); 
          for(int i=0; i<jsonArray.length(); i++) 
          { 
           college = new benedict.com.listviewpractice.cources(); 
           object = jsonArray.getJSONObject(i); 

           college.cources_name = object.getString("cource_name"); 
           college.cources_description = object.getString("cources_description"); 

           collegeList.add(college); 
          } 
         } 
         catch (JSONException e) { 
          // TODO Auto-generated catch block 
          e.printStackTrace(); 
         } 
        } 
       } 
       else 
       { 
        Toast.makeText(context, httpService.getErrorMessage(), Toast.LENGTH_SHORT).show(); 
       } 
      } 
      catch (Exception e) 
      { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 
      return null; 
     } 

     @Override 
     protected void onPostExecute(Void result) 

     { 
      proCollageList.setVisibility(View.GONE); 
      listCollege.setVisibility(View.VISIBLE); 
      if(collegeList != null) 
      { 
      ListAdapter adapter = new ListAdapter(collegeList, context); 
      listCollege.setAdapter(adapter); 
      } 
     } 
    } 
} 

Answer 1

內OnClickListener，this表示OnClickListener的實例，而不是您期望的上下文對象，因此this應該是MainActivity.this。

new GetHttpResponse(MainActivity.this).execute();