java - 安卓异步任务 : How to handle the return type

Question

我正在开发一个执行 http POST 请求 的 Android 应用程序，我遵循的教程导致了 android.os.NetworkOnMainThreadException

原始代码是这样的。

public class JSONParser {

static InputStream is = null;
static JSONObject jObj = null;
static String json = "";

// constructor
public JSONParser() {

}

public JSONObject getJSONFromUrl(String url, List<NameValuePair> params) {

    // Making HTTP request
    try {
        // defaultHttpClient
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);
        httpPost.setEntity(new UrlEncodedFormEntity(params));

        HttpResponse httpResponse = httpClient.execute(httpPost);
        HttpEntity httpEntity = httpResponse.getEntity();
        is = httpEntity.getContent();

    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        json = sb.toString();
        Log.e("JSON", 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
    return jObj;

}
}

并且用这一行调用了这个类。

JSONObject json = jsonParser.getJSONFromUrl(loginURL, params);

将其更改为 AsyncTask 类后，代码如下所示。

class JSONParser extends AsyncTask<String, Void, JSONObject>{

static InputStream is = null;
static JSONObject jObj = null;
static String json = "";

// variables passed in:
String url;
List<NameValuePair> params;

// constructor
public JSONParser(String url, List<NameValuePair> params) {
    this.url = url;
    this.params = params;
}

@Override
protected JSONObject doInBackground(String... args) {
    // Making HTTP request
        try {
            // defaultHttpClient
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);
            httpPost.setEntity(new UrlEncodedFormEntity(params));

            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();


        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }


        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();
            Log.e("JSON", 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
        return jObj;
}

@Override
protected void onPostExecute(JSONObject jObj) {
    return;
}       
}

我的问题是，如何从这个新的 AsyncTask 类返回一个 JSONObject？我可以看到 jObj 在 doInBackground()，但我不确定它返回到哪里。

我需要修改什么或者我需要如何调用我的新 JSONParser 类以便它返回 JSONObject？

Answer 1

看看这段代码，它可能会让您深入了解如何处理 JSON 对象的解析。我现在只是发布 onPostExecute 函数，因为您似乎已经正确计算了所有其他函数。

至于您对 doInBackground 中的数据对象返回位置的疑问，它会自动发送到 onPostExecute，您可以在其中进一步解析它。

            @Override
    protected void onPostExecute(JSONObject result)
    {
        try
        {   
            JSONObject data = result.getJSONObject("data");
                      // whatever your JSON tag may be, in this case its data.

            if (data.isNull("data"))
            {
                      // action to handle null JSON object.
            }               
            else
            {
                JSONArray jarray = data.getJSONArray("data");   
                int len=jarray.length();
                for (int i = 0; i < jarray.length(); i++)
                {
                JSONObject obj = (JSONObject) jarray.get(i);

             String instanceName = obj.getString("instanceName");   
                        //extract data by whatever tag names you require, in this case instanceName.    
           } 
         }
} 
        catch (JSONException je)
        {
            je.printStackTrace();
            Log.d(TAG, "Error: " + je.getMessage());
        }       
    }
}