按条件从doinBackground中途退出异步任务

Question

我正在从异步任务中加载数据。在doinBackground()中，我想检查返回的JSON字符串是否包含错误，如果是，我想停止asynctask并显示文本视图，如果没有错误，我想继续执行异步任务。这是我的密码。

protected String doInBackground(String... args) {
            // Building Parameters
            HttpClient client = new DefaultHttpClient();
            HttpPost post = new HttpPost(url_all_open_bets);
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            post.setHeader("User-Agent","Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/43.0.2357.81 Safari/537.36");
            params.add(new BasicNameValuePair("email", name));
            params.add(new BasicNameValuePair("User-Agent","Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/43.0.2357.81 Safari/537.36"));
            try {
                post.setEntity(new UrlEncodedFormEntity(params));
            } catch (IOException ioe) {
                ioe.printStackTrace();
            }
            try {
                HttpResponse response = client.execute(post);
                Log.d("Http Post Response:", response.toString());
                HttpEntity httpEntity = response.getEntity();
                InputStream is = httpEntity.getContent();
                JSONObject jObj = null;
                String json = "";
                try {
                    BufferedReader reader = new BufferedReader(new InputStreamReader(
                            is, "iso-8859-1"), 8);
                    StringBuilder sb = new StringBuilder();
                    String line = null;
                    while ((line = reader.readLine()) != null) {

                        if (!line.startsWith("<", 0)) {
                            if (!line.startsWith("(", 0)) {
                                sb.append(line + "\n");
                            }
                        }
                    }

                    is.close();
                    json = sb.toString();
                    json = json.substring(json.indexOf('{'));
                    if (json.contains("error")) {
                        TextView textView = (TextView) findViewById(R.id.nobetstxtbox);
                        textView.setVisibility(View.VISIBLE);
                    }
                    Log.d("sb", json);

                } catch (Exception e) {
                    Log.e("Buffer Error", "Error converting result " + e.toString());
                }

                // try parse the string to a JSON object
                try {
                    jObj = new JSONObject(json);
                } catch (JSONException e) {
                    Log.e("JSON Parser", "Error parsing data " + e.toString());
                }

                // return JSON String
                Log.d("json", jObj.toString());
                try {
                    allgames = jObj.getJSONArray(TAG_BET);
                    Log.d("allgames", allgames.toString());
                    ArrayList<BetDatabaseSaver> listofbets = new ArrayList<>();
                    // looping through All Products
                    for (int i = 0; i < allgames.length(); i++) {
                        JSONObject c = allgames.getJSONObject(i);

                        // Storing each json item in variable
                        String id = c.getString(TAG_ID);
                        String user = c.getString(TAG_USER);
                        String returns = c.getString(TAG_RETURNS);
                        String stake = c.getString(TAG_STAKE);
                        String status = c.getString(TAG_STATUS);
                        String Teams = c.getString(TAG_TEAMS);
                        Log.d("id", id);
                        Log.d("user", user);
                        Log.d("returns", returns);
                        Log.d("stake", stake);
                        Log.d("status", status);
                        Log.d("teams", Teams);


                        // creating new HashMap
                        HashMap<String, String> map = new HashMap<String, String>();

                        // adding each child node to HashMap key => value
                        map.put(TAG_ID, id);
                        map.put(TAG_TEAMS, Teams);
                        map.put(TAG_USER, user);
                        map.put(TAG_RETURNS, returns);
                        map.put(TAG_STAKE, stake);
                        map.put(TAG_STATUS, status);
                        useroutcomes.put(id.substring(0, 10), Teams);
                        boolean contains = false;
                        for (int a = 0; a < listwriter.size(); a++) {
                            if (listwriter.get(a).getId().equals(id)) {
                                listwriter.add(a, new BetDisplayer(user, id, Integer.parseInt(stake), Integer.parseInt(returns), status, "", "", Teams));
                                contains = true;
                            }
                        }
                        if (!(contains)) {
                            listwriter.add(i, new BetDisplayer(user, id, Integer.parseInt(stake), Integer.parseInt(returns), status, "", "", Teams));
                        }


                        // adding HashList to ArrayList
                        bet.add(map);
                    }


                } catch (JSONException e) {
                    e.printStackTrace();
                }
            } catch (IOException ioe) {
                ioe.printStackTrace();
            }


            return "";
        }

我添加了这个片段

` if (json.contains("error")) {
     TextView textView = (TextView) findViewById(R.id.nobetstxtbox);
     textView.setVisibility(View.VISIBLE);
            }`

以检查错误，但我不确定此时如何退出异步任务，如果错误为真，并且在此语句之后不执行任何代码。使用doesn将无法工作，因为它会干扰try catch语句，而使用catch也不起作用。

Answer 1

您可以在if条件下调用cancel()方法，在doInBackground()中调用cancel()将取消AsyncTask，而onCancelled()将被调用而不是onPostExecute()。

如下所示：

 if (json.contains("error")) {
       cancel(true);
       return "";  
 }

Answer 2

你可以在你的doInBackground()中做这样的事情

if (json.contains("error")) {
    return "error";
}

在你的onPostExecute()里

void onPostExecute(String message)
{
    if(message.equals("error"))
    {
         //You cannot access UI thread in doInBackground(). So, you need to do all the UI related tasks over here.
         TextView textView = (TextView) findViewById(R.id.nobetstxtbox);
         textView.setVisibility(View.VISIBLE);
    }

    else
    {
        //your code for the positive results
    }
}

Answer 3

您只需在条件中放置一个返回语句，它将以与退出任何方法相同的方式退出该方法(在本例中，它将退出到onPostExecute()方法)。