java - 看不懂android asyncTask

Question

我有一个应该获得 JSON 响应的方法。在这里:

public  HttpResponse getJson() {
        HttpResponse response = null;
        try {        
                HttpClient client = new DefaultHttpClient();
                HttpGet request = new HttpGet();
                request.setURI(new URI("https://mysite.com/android/showJson.php"));
                response = client.execute(request);
            } catch (URISyntaxException e) {
                e.printStackTrace();
            } catch (ClientProtocolException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }   
            return response;
        }

showJson.php 返回:["item 1","item 2"]

我面临的问题是我无法在 onCreate 中调用 getJson，因为它会抛出错误:android.os.NetworkOnMainThreadException

我注意到我的方法应该在一个单独的类中，以便在 onCreate 中调用它，但我无法管理它。真的要哭了，我看不懂asyncTask的语法!我知道我遗漏了一些小东西，但作为初学者我无法发现它。

这是 onCreate 方法:

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_top_jokes);    

        getJson();
        String[] myStringArray = {"a","b","c","a","b","c","a","b","c","a","b","c","a","b","c","a","b","c"};

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, 
                android.R.layout.simple_list_item_1, myStringArray);

        ListView listView = (ListView) findViewById(R.id.topJokesList);
        listView.setAdapter(adapter);

        listView.setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                // When clicked, show a toast with the TextView text
                Toast.makeText(getApplicationContext(),
                ((TextView) view).getText(), Toast.LENGTH_SHORT).show();
            }
        });

    }

我正在用一些测试值填充一个数组并将它们传递给 listView，但现在我需要用 getJson 的项目填充它。

Answer 1

你需要一个 AsyncTask ，您可以在 doInBackground 方法中执行请求。
收到响应后，您需要使用 onPostExecute 方法通知您的主线程 (ui)。

private class JsonTaskTask extends AsyncTask<Void, Void, Void> {
 private HttpResponse response;
 protected Long doInBackground(Void... params) {
     reponse = getJson();
     return null;
 }

 protected void onPostExecute(Void params) {
     //Show Your Listview
 }

 public  HttpResponse getJson() {
    HttpResponse response = null;
    try {        
            HttpClient client = new DefaultHttpClient();
            HttpGet request = new HttpGet();
            request.setURI(new URI("https://mysite.com/android/showJson.php"));
            response = client.execute(request);
        } catch (URISyntaxException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }   
        return response;
    }
  }

通过

调用你的AsyncTask

new JsonTaskTask().execute(void, void, void);

要通知您的 UI 并更新您的 ListView，您可以使用监听器界面。例如就像我在 this 中展示的那样回答。