java - Android 异步 Http 响应处理程序中的返回值

Question

我正在尝试在 Android 应用程序中从 MySQL 查询数据并将数据作为 ArrayList 返回。然而，当我得到它的大小时，ArrayList 是空的，就在 return 语句之上。下面是到目前为止我的代码。

public List<Application> getData(final Context cntx, final long startHere, String url) {
        final List<Application> apps = new ArrayList<Application>();
        AsyncHttpClient client = new AsyncHttpClient();

        RequestParams params = new RequestParams();
        params.put("startHere", startHere);
        client.post(url,
                params, new AsyncHttpResponseHandler() {

                    @Override
                    public void onFailure(int a0, Header[] a1, byte[] a2, Throwable a3) {
                      Toast.makeText(cntx,"Some Err", Toast.LENGTH_LONG).show();
                    }
                    @Override
                    public void onSuccess(int statusCode, Header[] header,
                            byte[] response) {
                        String s = new String(response);

                        try {
                        JSONArray aJson = new JSONArray(s);

                        for(int i=0; i<aJson.length(); i++) {
                            JSONObject json = aJson.getJSONObject(i);
                            Application app = new Application();
                            app.setTitle(json.getString("app_title")); 
                            app.setIcon(json.getString("icon"));

                            // works here as expected, returns values > 0
                            Log.i("Debug 1", apps.size()+"");
                            apps.add(app);
                        }

                        Toast.makeText(cntx, apps.size()+"", Toast.LENGTH_LONG).show();

                    } catch (JSONException e) {
                        Toast.makeText(cntx, "Invalid JSON", Toast.LENGTH_LONG).show();
                    }  
                    }

                });
        //Does not work at this point, returns a value of 0!
        Log.i("Debug 2", apps.size()+"");
        return apps;
    }

Answer 1

试试这个:

public class HomeFragment extends Fragment {
private ListView mListView;
private ListViewNewsAdapter listViewNewsAdapter;
private ArrayList<ListViewNewsItem> listViewNewsItems;
private ImageView Right ;
private ImageView Left ;
private  String NewsBody[] ;
private TimerTask mTimerTask;
private Timer timer = new Timer();
private boolean Switch = true ;





private final Handler timerHandler = new Handler();


private JSONParser jsonParser = new JSONParser();

private String READNEWS_URL =
        "YOUR WEBSITE";



public HomeFragment() {
    // Required empty public constructor
}

@TargetApi(Build.VERSION_CODES.JELLY_BEAN)
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.fragment_home, container, false);
    mListView = (ListView) rootView.findViewById(R.id.mlv);
    Right = (ImageView) rootView.findViewById(R.id.adv_right) ;
    Left = (ImageView) rootView.findViewById(R.id.adv_left) ;
    Animation LeftSideAnimation = AnimationUtils.loadAnimation(getActivity(), R.anim.blink);
    Right.startAnimation(LeftSideAnimation);
    Left.startAnimation(LeftSideAnimation);
    Left.setBackground(getResources().getDrawable(R.drawable.facebook_icon));
    Right.setBackground(getResources().getDrawable(R.drawable.home_icon));


    new GetNewsTask().execute();
    mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position,
                                long id) {
            Show_News_Body Show_News_Body = new Show_News_Body(getActivity(), NewsBody[position]);
            Show_News_Body.show();


        }
    });


    return rootView;
}

private class GetNewsTask extends AsyncTask<Void, Void, Boolean>
{
    private ProgressDialog mProgressDialog;

    private JSONObject jsonObjectResult = null;

    private String error;

    @Override
    protected void onPreExecute()
    {
        super.onPreExecute();
        listViewNewsItems = new ArrayList<ListViewNewsItem>();
        mProgressDialog = ProgressDialog.show(getActivity(),
                "Processing...", "Get last news", false, false);
    }

    @Override
    protected Boolean doInBackground(Void... params)
    {
        jsonObjectResult = jsonParser.makeHttpRequest(READNEWS_URL, null);

        if (jsonObjectResult == null)
        {
            error = "Error in the connection";
            return false;
        }

        try
        {
            if (jsonObjectResult.getInt("success") == 1)
            {
                JSONArray jsonArray = jsonObjectResult.getJSONArray("posts");
                NewsBody = new String[jsonArray.length()];
                for (int i = 0; i < jsonArray.length(); i++)
                {
                    JSONObject news = jsonArray.getJSONObject(i);
                    ListViewNewsItem listViewNewsItem = new ListViewNewsItem
                            (
                                    news.getString("title"),
                                    news.getString("type"),
                                    news.getString("image_link"),
                                    news.getString("news_body")
                            );
                    listViewNewsItems.add(listViewNewsItem);
                    NewsBody[i]= listViewNewsItem.getNews_body();

                }
                return true;
            }
            else
                error = jsonObjectResult.getString("message");

        }
        catch (Exception ex)
        {

        }

        return false;
    }

    @Override
    protected void onPostExecute(Boolean aBoolean)
    {
        super.onPostExecute(aBoolean);
        mProgressDialog.dismiss();
        if (aBoolean)
        {
            listViewNewsAdapter = new ListViewNewsAdapter(getActivity(),
                    listViewNewsItems);
            mListView.setAdapter(listViewNewsAdapter);
        }
        else
            Toast.makeText(getActivity(), error, Toast.LENGTH_LONG).show();
    }
}

}

这是我的布局包含一个像这样的 ListView :

<ListView
    android:layout_marginTop="2dp"
    android:layout_below="@+id/line_adv"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background = "@android:color/transparent"
    android:padding="3dp"
    android:dividerHeight="1dp"
    android:id="@+id/mlv"></ListView>

还有另外两个类:

public class ListViewNewsAdapter extends ArrayAdapter<ListViewNewsItem> {

private Context mContext;
private ArrayList<ListViewNewsItem> mData;

public ListViewNewsAdapter (Context mContext, ArrayList<ListViewNewsItem> mData) {
    super(mContext, R.layout.data_shape, mData);
    this.mContext = mContext;
    this.mData = mData;
}

@Override
public int getCount() {
    return mData.size();
}

@Override
public long getItemId(int position) {
    return position;
}

@Override
public View getView(final int position, View convertView, ViewGroup parent)
{
    if (convertView == null)
    {
        LayoutInflater mInflater = (LayoutInflater)
                mContext.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
        convertView = mInflater.inflate(R.layout.data_shape, null);
    }
    TextView m_title = (TextView) convertView.findViewById(R.id.m_title);
    m_title.setText(mData.get(position).getM_title());


    TextView m_type = (TextView) convertView.findViewById(R.id.m_type);
    m_type.setText(mData.get(position).getM_type());

    UrlImageViewHelper.setUrlDrawable((ImageView) convertView.findViewById(R.id.NewsImage),
            mData.get(position).getImage_link()
            , R.drawable.ic_launcher, 60000);

    return convertView;
}

还有这个:

public class ListViewNewsItem {


private String m_title ;
private String m_type;
private String image_link ;
private String news_body ;


public ListViewNewsItem( String m_title, String m_type,String image_link, String news_body ) {
    this.m_title = m_title;
    this.m_type = m_type ;
    this.image_link = image_link ;
    this.news_body = news_body ;
}

public String getNews_body() {
    return news_body;
}

public void setNews_body(String news_body) {
    this.news_body = news_body;
}

public String getImage_link() {
    return image_link;
}

public void setImage_link(String image_link) {
    this.image_link = image_link;
}

public void setM_title(String m_title) {
    this.m_title = m_title;
}

public String getM_title() {
    return m_title;
}

public void setM_type(String m_type) {
    this.m_type = m_type;
}

public String getM_type() {
    return m_type;
}
 }

Data_Shape 布局如下:

<?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_margin="5dp"
android:paddingTop="10dp"
android:layout_height="match_parent">

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">
    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="2"
        android:orientation="vertical">
        <TextView
            android:layout_margin="5dp"
            android:layout_width="match_parent"
            android:layout_weight="1"
            android:layout_height="0dp"
            android:text="The Title Is Here"
            android:textDirection="rtl"
            android:textColor="#173966"
            android:textSize="15dp"
            android:id="@+id/m_title"/>
        <TextView

            android:layout_height="wrap_content"
            android:id="@+id/m_type"
            android:layout_marginLeft="5dp"
            android:textSize="10dp"
            android:layout_width="match_parent"
            android:text="HERE IS THE TEXT"
            android:textColor="@android:color/black"/>

    </LinearLayout>
    <ImageView
        android:layout_width="70dp"
        android:layout_height="70dp"
        android:id="@+id/NewsImage"/>




   </LinearLayout>

 </LinearLayout>

请注意，您的 MYSQL 表应包含以下列:标题、类型、图像链接和正文。