如果在Android中獲取空值，如何從JSON解析中吐出“找不到數據”

Question

我從URL解析JSON值（如果我得到null值），所以我想Toast “找不到數據”
我的代碼在這里

    @Override
    protected List<Details> doInBackground(String... params) {
        List<Details> result = new ArrayList<Details>();
        ServiceHandler serviceHandler=new ServiceHandler(TrainshwstnActivity.this);
            String u = new String(params[0]);
            String JsonStr=serviceHandler.makeServiceCall(u, ServiceHandler.GET);
            Log.d("Response: ", "> " + JsonStr);
               if (JsonStr != null) {
                    try {                       
                    JSONArray arr = new JSONArray(JsonStr);
                    for (int i=0; i < arr.length(); i++) {
                        result.add(convertContact(arr.getJSONObject(i)));
                    }

                    return result;
                }
                catch(Throwable t) {
                    t.printStackTrace();
                }
                return null;
            }
        return result;
        }

Answer 1

在doInbackground代碼之后添加代碼：

protected void onPostExecute(String result) {
     if(result == null){
     Toast.makeText(getApplicationContext(),"No data found", Toast.LENGTH_LONG).show();
     }
 }