Question

我正在尝试从InBackground方法获取返回值，该方法是第一次获取，然后返回正确，但是返回NULL后，我的逻辑如下：在onPostExecute方法中，我调用另一个函数来设置变量的值，但是由于某种原因，该变量在正确接收数据后变为NULL。这是我的代码：

if (TextUtils.isEmpty(firstname))
{
    Toast.makeText(Signup.this, "Enter your first name.", Toast.LENGTH_LONG).show();
} else if (TextUtils.isEmpty(lastname))
{
    Toast.makeText(Signup.this, "Enter your last name.", Toast.LENGTH_LONG).show();
} else if (TextUtils.isEmpty(email))
{
    Toast.makeText(Signup.this, "Enter your valid email address.", Toast.LENGTH_LONG).show();
}else if (TextUtils.isEmpty(password))
{
    Toast.makeText(Signup.this, "Enter your password.", Toast.LENGTH_LONG).show();
} else if (TextUtils.isEmpty(confirmpass)) {
    Toast.makeText(Signup.this, "Please write your password again.", Toast.LENGTH_LONG).show();
}else if (password != confirmpass)
{
    Toast.makeText(Signup.this, "Password do not match", Toast.LENGTH_LONG).show();
}

Answer 1

我认为，将结果提供回调用代码的更好方法是使用接口，例如：

interface RequestListener {
   public onResultSuccess(JSONArray array);
   public onResultFail(String error);
}

private class MyTask extends AsyncTask<String, Void, JSONArray>
{
    RequestListener listener = null;

    MyTask(RequestListener listener) {
       this.listener = listener
    }

    @Override
    protected JSONArray doInBackground(String... urls)
    {
        try{
            URL url = new URL(urls[0]);
            HttpURLConnection myConnection =
                    (HttpURLConnection) url.openConnection();

            if (myConnection.getResponseCode() == 200) {
                InputStream responseBody = myConnection.getInputStream();

                InputStreamReader responseBodyReader =
                        new InputStreamReader(responseBody, "UTF-8");

                BufferedReader streamReader = new BufferedReader(new InputStreamReader(responseBody, "UTF-8"));
                StringBuilder responseStrBuilder = new StringBuilder();

                String inputStr;
                while ((inputStr = streamReader.readLine()) != null)
                    responseStrBuilder.append(inputStr);

                JSONArray jsonArray = new JSONArray(responseStrBuilder.toString());

                //myConnection.disconnect();
                return jsonArray;
            } else {
                return null;
            }
        }catch (Exception e){
            return null;
        }

    }

    @Override
    protected void onPostExecute(JSONArray jsonArray)
    {
        if (listener != null) {
           if (jsonArray != null) {
              listener.onResultSuccess(jsonArray);
           } else {
              listener.onResultFail(your-message);
           }
        } 
    }
}

然后，当您实例化RequestListener对象（可能在MyTask内）时，您当然必须提供onCreate接口的实例

从AsyncTask获得回报

1 个答案: