java - 使用 AsyncTask 检查列表

Question

当我从服务器获取列表时遇到问题，我想检查它是否有任何对象。如果有对象，出现在我的布局文本中:几秒钟后没有对象，它就会消失 并显示我的列表。

我想要如果有对象就会直接出现在我的布局中。 私有(private)类 RetrieveTask 扩展 AsyncTask> {

    @Override
    protected List<branch> doInBackground(String... params) {

        manager = new SessionManager(getActivity().getApplicationContext());
        manager.checkLogin();
        HashMap<String, String> user = manager.getUserID();
        String uid = user.get(SessionManager.KEY_uid);
       // Intent intent= getActivity().getIntent(); // gets the previously created intent
        //String type18 = intent.getStringExtra("key28");
        String strUrl = 

        HttpURLConnection connection = null;
        BufferedReader reader = null;

        try {
            URL url = new URL(strUrl);
            connection = (HttpURLConnection) url.openConnection();
            connection.connect();
            InputStream stream = connection.getInputStream();
            reader = new BufferedReader(new InputStreamReader(stream));
            StringBuffer buffer = new StringBuffer();
            String line = "";
            while ((line = reader.readLine()) != null) {
                buffer.append(line);
            }

            String finalJson = buffer.toString();

            JSONObject parentObject = new JSONObject(finalJson);
            JSONArray parentArray = parentObject.getJSONArray("markers");

            ////////////////////////////////////////
            List<branch> bList = new ArrayList<>();

            Gson gson = new Gson();
            for (int i = 0; i < parentArray.length(); i++) {
                JSONObject finalObject = parentArray.getJSONObject(i);

                /////////market object
                market mr = new market(Integer.valueOf(finalObject.getString("id")), finalObject.getString("mName")
                        , finalObject.getString("pic"));

                /////////location object
                location lo = new location(Float.valueOf(finalObject.getString("lat")), Float.valueOf(finalObject.getString("lng"))
                        , finalObject.getString("area"), finalObject.getString("city"));


                /////////(branch object) inside it (market object)
                branch it = new branch(Integer.valueOf(finalObject.getString("bid")), Integer.valueOf(finalObject.getString("phone"))
                        , finalObject.getString("ser"), Integer.valueOf(finalObject.getString("dis")), Integer.valueOf(finalObject.getString("brNo"))
                        , Float.valueOf(finalObject.getString("rating")), mr, lo,true);

                /*//////////add marker
                LatLng latlng = new LatLng(Double.valueOf(finalObject.getString("lat")), Double.valueOf(finalObject.getString("lng")));
                addMarker(latlng, Integer.valueOf(finalObject.getString("bid")));*/

                // adding the branch object in the list
                bList.add(it);
            }
            return bList;

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        } finally {
            if (connection != null) {
                connection.disconnect();
            }
            try {
                if (reader != null) {
                    reader.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        return null;

    }

这里是 postExcute

    @Override
    protected void onPostExecute(final List<branch> result) {
        super.onPostExecute(result);

        if (result != null) {

            final itemAdapter adapter = new itemAdapter(getActivity().getApplicationContext(), R.layout.row_favmarkets, result);
            lv.setAdapter(adapter);


        }
    }

}

这是我的布局 xml

  <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="4dp"
android:paddingLeft="4dp"
android:paddingRight="4dp"
android:paddingTop="4dp"
tools:context="com.gmplatform.gmp.favouriteitem">
<LinearLayout
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/textView28"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="40dp"
        android:layout_marginTop="250dp"
        android:text="There is no Markets in your Favourite List.."
        android:textSize="24sp"
        android:visibility="gone" />
</LinearLayout>

<ListView
    android:id="@+id/l20"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_centerHorizontal="true"
    android:layout_centerVertical="true"
    android:horizontalSpacing="3dp"
    android:numColumns="3"
    android:verticalSpacing="0dp" />
<Button
    android:text="Button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/button6"
    android:layout_marginLeft="400dp" />

Answer 1

建议的更改在执行请求时首先不会显示任何内容。完成后，如果列表为空，它将显示“您最喜欢的列表中没有市场..”，否则将显示该列表。

零件布局 XML:

<LinearLayout
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/linearLayout28">

    <TextView
        android:id="@+id/textView28"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="40dp"
        android:layout_marginTop="250dp"
        android:text="There is no Markets in your Favourite List.."
        android:textSize="24sp"
        android:visibility="gone" />
</LinearLayout>

初始化linearLayout28 :

LinearLayout linearLayout28 = findViewById(R.id.linearLayout28);

AsyncTask 的更改:

private class RetrieveTask extends AsyncTask<Void, Void, List<branch>> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        lv.setVisibility(View.GONE);
        linearLayout28.setVisibility(View.GONE);
    }

    @Override
    protected List<branch> doInBackground(String... params) {
        //Keep as your code
        ...
    }

    @Override
    protected void onPostExecute(final List<branch> result) {
        super.onPostExecute(result);

        if (result != null && result.size() != 0) {
            final itemAdapter adapter = new itemAdapter(
                getActivity().getApplicationContext(),
                R.layout.row_favmarkets, result);
            lv.setAdapter(adapter);
            lv.setVisibility(View.VISIBLE);
            linearLayout28.setVisibility(View.GONE);
        } else {
            lv.setVisibility(View.GONE);
            linearLayout28.setVisibility(View.VISIBLE);
        }
    }
}