Android Studio中AsyncTask获取JSON，onPostExecute不执行问题求助

尝试从Pastebin的JSON文件获取数据并加载到ListView时，调用execute后onPreExecute正常执行，但onPostExecute完全没触发。

点击事件代码 #

public void onClick(View view) {
    ExtragereJSON extragereJSON = new ExtragereJSON() {
        ProgressDialog progressDialog;
      
        @Override
        protected void onPreExecute() {
            progressDialog = new ProgressDialog(Proba_Practica_Petrescu_Rares_Mihnea.this);
            progressDialog.setMessage("Please wait...");
            progressDialog.show();
        }

        @Override
        protected void onPostExecute(String s) {
            //progressDialog.setMessage("Done...");
            //progressDialog.show();
            progressDialog.cancel();
            if (s != null) {
                listaInregistrari.addAll(this.listaRestaurante);
                // CustomAdapter adaptorNou = new CustomAdapter(getApplicationContext(), R.layout.listviewrestaurante_layout,
                // getLayoutInflater(), listaInregistrari);
                Log.d("AsyncTask", "onPostExecute: JSON extraction successful");
            } else {
                // Handle the case where the JSON extraction failed
                // Log or display an error message
                Log.e("AsyncTask", "onPostExecute: Failed to extract JSON");
            }
        }

    };
    try {
        extragereJSON.execute(new URL("https://pastebin.com/raw/vVBcgK7H"));
    } catch (MalformedURLException e) {
        Log.e("URLValidationError", "Malformed URL: " + e.getMessage());
        e.printStackTrace();
    } catch (Exception e) {
        // Log or display a general error message
        Log.e("ExtractionError", "Failed to extract JSON: " + e.getMessage());
        e.printStackTrace();
    }
}

ExtragereJSON类实现 #

public class ExtragereJSON extends AsyncTask<URL,Void,String> {

    public List<InregistrareRestaurant> listaRestaurante=new ArrayList<>();
    @Override
    protected String doInBackground(URL... urls) {

        try {
            HttpURLConnection connection=(HttpURLConnection) urls[0].openConnection();
            connection.setRequestMethod("GET");
            InputStream inputStream=connection.getInputStream();

            InputStreamReader isr=new InputStreamReader(inputStream);
            BufferedReader br=new BufferedReader(isr);
            String line=null;
            String rezultat="";
            while((line=br.readLine())!=null)
                rezultat+=line;
            parsareJSON(rezultat);

            return rezultat;
        } catch (IOException e) {
            Log.e("AsyncTask", "Exception in doInBackground: " + e.getMessage());
            return null; // Return null or an error message
        }
    }
    private void parsareJSON(String result){

        if(result!=null){
            try{
                JSONObject obiect=new JSONObject(result);

                    JSONArray restaurante = obiect.getJSONArray("restaurante");
                    for (int i = 0; i < restaurante.length(); i++) {
                        JSONObject restaurant = restaurante.getJSONObject(i);
                        int codRestaurant = restaurant.getInt("codRestaurant");
                        String numeRestaurant = restaurant.getString("numerestaurant");
                        int capacitate = restaurant.getInt("capacitate");
                        float venituri = (float) restaurant.getDouble("venituri");
                        String tipRestaurant = restaurant.getString("tipRestaurant");
                        InregistrareRestaurant ir = new InregistrareRestaurant(codRestaurant, numeRestaurant, capacitate, venituri, tipRestaurant);
                        listaRestaurante.add(ir);

                }
            } catch (Exception e) {
                throw new RuntimeException(e);
            }

        }
        else
        {
            Log.e("parsareJSON","JSON este null");
        }
    }

}

问题原因分析 #

核心问题出在parsareJSON方法的异常处理：当JSON解析过程中出现任何异常时，代码直接抛出RuntimeException，而这个异常没有在doInBackground中被捕获。AsyncTask的后台任务一旦遇到未捕获的异常，会直接终止，不会执行return语句，也就不会触发onPostExecute，而是会调用onCancelled方法（如果有重写的话）。

另外，网络请求的资源（HttpURLConnection、InputStream、BufferedReader）没有关闭，可能导致资源泄漏，但这不是onPostExecute不触发的直接原因。

解决步骤 #

1. 修复JSON解析的异常处理
   不要抛出RuntimeException，而是捕获异常后记录日志，确保doInBackground能正常返回结果：

   private void parsareJSON(String result){
       if(result!=null){
           try{
               JSONObject obiect=new JSONObject(result);
               JSONArray restaurante = obiect.getJSONArray("restaurante");
               for (int i = 0; i < restaurante.length(); i++) {
                   JSONObject restaurant = restaurante.getJSONObject(i);
                   int codRestaurant = restaurant.getInt("codRestaurant");
                   String numeRestaurant = restaurant.getString("numerestaurant");
                   int capacitate = restaurant.getInt("capacitate");
                   float venituri = (float) restaurant.getDouble("venituri");
                   String tipRestaurant = restaurant.getString("tipRestaurant");
                   InregistrareRestaurant ir = new InregistrareRestaurant(codRestaurant, numeRestaurant, capacitate, venituri, tipRestaurant);
                   listaRestaurante.add(ir);
               }
           } catch (Exception e) {
               Log.e("parsareJSON", "JSON解析失败: " + e.getMessage());
               e.printStackTrace();
               // 可以选择清空列表，避免添加无效数据
               listaRestaurante.clear();
           }
       } else {
           Log.e("parsareJSON","JSON内容为空");
       }
   }
   

2. 添加资源关闭逻辑
   在doInBackground中使用try-with-resources或者手动关闭网络连接和流，防止资源泄漏：

   @Override
   protected String doInBackground(URL... urls) {
       HttpURLConnection connection = null;
       BufferedReader br = null;
       try {
           connection=(HttpURLConnection) urls[0].openConnection();
           connection.setRequestMethod("GET");
           InputStream inputStream=connection.getInputStream();
           InputStreamReader isr=new InputStreamReader(inputStream);
           br=new BufferedReader(isr);
           String line=null;
           StringBuilder rezultat=new StringBuilder(); // 用StringBuilder代替字符串拼接，更高效
           while((line=br.readLine())!=null)
               rezultat.append(line);
           parsareJSON(rezultat.toString());
           return rezultat.toString();
       } catch (IOException e) {
           Log.e("AsyncTask", "网络请求异常: " + e.getMessage());
           e.printStackTrace();
           return null;
       } finally {
           // 关闭资源
           if (br != null) {
               try {
                   br.close();
               } catch (IOException e) {
                   e.printStackTrace();
               }
           }
           if (connection != null) {
               connection.disconnect();
           }
       }
   }
   

3. 重写onCancelled方法（可选但推荐）
   重写该方法可以处理任务崩溃或被取消的情况，避免ProgressDialog一直显示：

   @Override
   protected void onCancelled() {
       super.onCancelled();
       if (progressDialog != null && progressDialog.isShowing()) {
           progressDialog.cancel();
       }
       Log.e("AsyncTask", "任务被取消/崩溃");
   }
   

4. 检查JSON数据结构
   确认Pastebin返回的JSON结构与解析逻辑匹配，比如键名是否正确（比如numerestaurant是否确实是JSON中的字段名），避免因字段不存在导致解析异常。

内容的提问来源于stack exchange，提问作者Rares Petrescu