Question

我在活动中有以下代码：

ListView lv = (ListView) findViewById(R.id.listViewPizza2);
    try {
        URL url = new URL("http://api.androidhive.info/pizza/?format=xml");
        HttpURLConnection http = (HttpURLConnection)url.openConnection();
        http.setDoInput(true);
        http.connect();
        InputStream in = http.getInputStream();
        XmlPullParserPizza2 parser_Pizza = new XmlPullParserPizza2();
        pizzaList = parser_Pizza.parse(in);
        BinderDataPizza bd_Pizza = new BinderDataPizza(this, pizzaHashmap);
        lv.setAdapter(bd_Pizza);
    }
    catch (Exception e) {
        e.printStackTrace();
    }

如何使用AsyncTask HttpURLConnection来完成这项工作？

Answer 1

将要执行的代码放在doInBackground的后台。但是，您应该在UI线程上保留UI更新代码，因此请在onPostExecute（在您调用execute()的同一线程上安排）中调用它。

以下是转换代码的简单方法：

final ListView lv = (ListView) findViewById(R.id.listViewPizza2);
new AsyncTask<Void, Void, BinderDataPizza>() {
  @Override
  protected BinderDataPizza doInBackground(Void... params) {
    try {
      URL url = new URL("http://api.androidhive.info/pizza/?format=xml");
      HttpURLConnection http = (HttpURLConnection)url.openConnection();
      http.setDoInput(true);
      http.connect();
      InputStream in = http.getInputStream();
      XmlPullParserPizza2 parser_Pizza = new XmlPullParserPizza2();
      pizzaList = parser_Pizza.parse(in);
      BinderDataPizza bd_Pizza = new BinderDataPizza(this, pizzaHashmap);
      return bd_Pizza;
    } catch (Exception e) {
      Log.e("MyApp", "error while fetching", e);
    }
    return null;
  }
  @Override
  protected void onPostExecute(BinderDataPizza bd_Pizza) {
    if (bd_Pizza != null)
      lv.setAdapter(bd_Pizza);
  }
}.execute();

Answer 2

<强> 1。创建异步任务

class GetDataAsyncTask extends AsyncTask<Void, Void, Void> {


    List<Pizza> pizzaList = new ArrayList<>();

    Context context;
    ListView lv;
    public GetDataAsyncTask(Context context, ListView lv) {
        this.lv = lv;
        this.context = context;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected Void doInBackground(Void... arg0) {

        try {
            URL url = new URL("http://api.androidhive.info/pizza/?format=xml");
            HttpURLConnection http = (HttpURLConnection)url.openConnection();
            http.setDoInput(true);
            http.connect();
            InputStream in = http.getInputStream();
            XmlPullParserPizza2 parser_Pizza = new XmlPullParserPizza2();
            pizzaList = parser_Pizza.parse(in);
            }
        catch (Exception e) {
            e.printStackTrace();
        }

        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);
        BinderDataPizza bd_Pizza = new BinderDataPizza(this, pizzaList);
        lv.setAdapter(bd_Pizza);

    }
}

<强> 2。执行异步任务

ListView lv = (ListView) findViewById(R.id.listViewPizza2);

new GetDataAsyncTask(context, lv).execute(); 
//Use following code if you want to run multiple async tasks in parallel
new GetDataAsyncTask(context, lv).executeOnExecutors(AsyncTask.THREAD_POOL_EXECUTOR)

Answer 3

您可以创建私人自定义类。

 private class GetData extends AsyncTask<Void, Void, Void> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            // Showing progress dialog


        }

        @Override
        protected Void doInBackground(Void... arg0) {

            // Making a request to url and getting response
            String jsonStr = makeServiceCall(your_url);//**call your http request in this method**


    JSONArray contacts = null;
            Log.d("Response: ", "> " + jsonStr);

            if (jsonStr != null) {
                try {
                    JSONObject jsonObj = new JSONObject(jsonStr);

                    // Getting JSON Array node
                    contacts = jsonObj.getJSONArray(YOUR_JSON_ARRAY_TAG);

                    // looping through All Contacts
                    for (int i = 0; i < contacts.length(); i++) {
                        //parse ur json object and save values in your model class
                    }
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            } else {
                Log.e("ServiceHandler", "Couldn't get any data from the url");
            }

            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            // Dismiss the progress dialog

             * Updating parsed JSON data in your UI
             * */

        }

    }

您可以通过以下方式致电：

 // Calling async task to get json
    new GetData ().execute();

Answer 4

private class PrefetchData extends AsyncTask<Void, Void, InputStream> {


    @Override
    protected void onPreExecute() {
        super.onPreExecute();

    }

    @Override
    protected String doInBackground(Void... arg0) {
    InputStream in = null;
     try {
     URL url = new URL("http://api.androidhive.info/pizza/?format=xml");
    HttpURLConnection http = (HttpURLConnection)url.openConnection();
    http.setDoInput(true);
    http.connect();
    InputStream in = http.getInputStream();
     }
    catch (Exception e) {
        e.printStackTrace();
     }
        return in;
    }

    @Override
    public void onPostExecute(InputStream result) {
        super.onPostExecute(result);
        XmlPullParserPizza2 parser_Pizza = new XmlPullParserPizza2();
    pizzaList = parser_Pizza.parse(in);
    BinderDataPizza bd_Pizza = new BinderDataPizza(this, pizzaHashmap);
    lv.setAdapter(bd_Pizza);
    }
}

并以这种方式召唤它！

new PrefetchData().execute();

Android将代码更改为AsyncTask

4 个答案: