java - 从 AsyncTask 添加数据的 Android Listview 问题

Question

我正在使用带有 lazyadapter 的 android listview 在列表中显示图像和 TextView 。

当用户滚动到底部时，我正在使用 AsyncTask 添加更多内容，但是当我执行 AsyncTask 时，它会终止进程。

这是我的代码。主要 Activity

import java.util.ArrayList;
import java.util.HashMap;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import org.w3c.dom.NodeList;



import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.sax.Element;
import android.view.View;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.Button;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.TextView;

public class AndroidJSONParsingActivity extends Activity {

    // url to make request


    // JSON Node names
    static final String TAG_CONTACTS = "comics";
    static final String TAG_ID = "id";
    static final String TAG_NAME = "title";
    static final String TAG_EMAIL = "id";
    static final String TAG_PHONE_MOBILE = "image";

    // contacts JSONArray
    JSONArray contacts = null;
    ListView list;
    LazyAdapter adapter;
    static int counter = 0;
    ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>();
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    list=(ListView)findViewById(R.id.list);
                    // call the function
    LoadData();

}

public void LoadData(){


      String url = "http://myurl?start=" + counter;


            // Creating JSON Parser instance
            JSONParser jParser = new JSONParser();

            // getting JSON string from URL
            JSONObject json = jParser.getJSONFromUrl(url);

            try {
                // Getting Array of Contacts
                contacts = json.getJSONArray(TAG_CONTACTS);

                // looping through All Contacts
                for(int i = 0; i < contacts.length(); i++){
                    JSONObject c = contacts.getJSONObject(i);

                    // Storing each json item in variable
                    String id = c.getString(TAG_ID);
                    String name = c.getString(TAG_NAME);
                    String email = c.getString(TAG_EMAIL);
                    String mobile = "http://www.funnydash.com/uploads/s/" + c.getString(TAG_PHONE_MOBILE);
                    // Phone number is agin JSON Object

                    // creating new HashMap
                    HashMap<String, String> map = new HashMap<String, String>();

                    // adding each child node to HashMap key => value
                    map.put(TAG_ID, id);
                    map.put(TAG_NAME, name);
                    map.put(TAG_EMAIL, email);
                    map.put(TAG_PHONE_MOBILE, mobile);

                    // adding HashList to ArrayList
                    contactList.add(map);
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }


            /**
             * Updating parsed JSON data into ListView
             * */

            // Getting adapter by passing xml data ArrayList
            adapter=new LazyAdapter(this, contactList);        
            list.setAdapter(adapter);



            list.setOnScrollListener(new EndlessScrollListener());

}

public class BackgroundLoadMore extends AsyncTask<Void, Void, Void> {

      @Override
        protected void onPreExecute() {
            // Showing progress dialog before sending http request


        }

    protected Void doInBackground(Void... unused) {
        LoadData();

        return (null);


    }

    protected void onPostExecute(Void unused) {
        // On completing background task
        // closing progress dialog etc,.
        list.setOnScrollListener(new EndlessScrollListener());

        }

}

      public class EndlessScrollListener implements OnScrollListener {

            private int visibleThreshold = 0;
            private int currentPage = 0;
        private int previousTotal = 0;
        private boolean loading = true;

        public EndlessScrollListener() {
        }
        public EndlessScrollListener(int visibleThreshold) {
            this.visibleThreshold = visibleThreshold;
        }

        @Override
        public void onScroll(AbsListView view, int firstVisibleItem,
                int visibleItemCount, int totalItemCount) {
            if (loading) {
                if (totalItemCount > previousTotal) {
                    loading = false;
                    previousTotal = totalItemCount;
                    counter +=12;
                }
            }
            if (!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)) {
                // I load the next page of gigs using a background task,
                // but you can call any function here.
                new BackgroundLoadMore().execute();
                loading = true;
            }
        }

        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {
        }
    }

Lazyadapter.java

import java.util.ArrayList;
import java.util.HashMap;

import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class LazyAdapter extends BaseAdapter {

    private Activity activity;
    private ArrayList<HashMap<String, String>> data;

    private static LayoutInflater inflater=null;
    public ImageLoader imageLoader; 



    public LazyAdapter(Activity a, ArrayList<HashMap<String, String>> d) {
        activity = a;
        data=d;
        inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        imageLoader=new ImageLoader(activity.getApplicationContext());
    }

    public int getCount() {
        return data.size();
    }

    public Object getItem(int position) {
        return position;
    }

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


    public View getView(int position, View convertView, ViewGroup parent) {
        View vi=convertView;
        if(convertView==null)
            vi = inflater.inflate(R.layout.list_row, null);

        TextView title = (TextView)vi.findViewById(R.id.title); // title
        TextView artist = (TextView)vi.findViewById(R.id.artist); // artist name

        ImageView thumb_image=(ImageView)vi.findViewById(R.id.list_image); // thumb image

        HashMap<String, String> song = new HashMap<String, String>();
        song = data.get(position);



        // Setting all values in listview

    title.setText(song.get(AndroidJSONParsingActivity.TAG_NAME));
    artist.setText(song.get(AndroidJSONParsingActivity.TAG_ID));

    imageLoader.DisplayImage(song.get(AndroidJSONParsingActivity.TAG_PHONE_MOBILE), thumb_image);
    return vi;
}

和this是我在我的 logcat 中得到的

Answer 1

问题是因为您试图从 UI 线程外部在您的列表中设置一个适配器。 Android 中的 View 不能在后台线程中修改，在这种情况下，这意味着您不能从 doInBackground 修改 UI AsyncTask 的方法.所以，你的方法 LoadData()不能调用以下内容:

adapter=new LazyAdapter(this, contactList);        
list.setAdapter(adapter);
list.setOnScrollListener(new EndlessScrollListener());

您需要从 contactList 返回一些数据(可能是 doInBackground() )方法，然后将有问题的代码移至 onPostExecute()方法，它是在 UI 线程上运行。

堆栈跟踪中记录的关键问题是:

CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.