首页 > 代码库 > ★android开发--ListView+Json+异步网络图片加载+滚动翻页的例子（图片能缓存，图片不错乱）

★android开发--ListView+Json+异步网络图片加载+滚动翻页的例子（图片能缓存，图片不错乱）

2024-07-18 12:18:42   219人阅读

例子中用于解析Json的Gson请自己Google下载

主Activity：

package COM.Example.Main;

import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

import COM.Example.Main.R;
import COM.Example.Main.stringGetJson.User;
import android.app.Activity;
import android.app.ListActivity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.TextView;

public class stringListActivity extends ListActivity {

    private MyAdapter mMyAdapter;
    private LinkedList<User> users = null;
    // 当前Activity中的ListView
    ListView listView = null;
    int lastItem = 0;
    LinearLayout loadingLayout = null;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.foodlistactivity);

        listView = getListView();
        setLoadingLayout();
        new readTask().execute(null);
    }

    private final class MyAdapter extends ArrayAdapter<User> {
        public MyAdapter(Activity activity, List<User> newsList) {
            super(activity, 0, newsList);
        }

        private Map<Integer, View> viewMap = new HashMap<Integer, View>();

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            ViewHolder holder;

            View rowView = this.viewMap.get(position);

            if (rowView == null) {
                User user = users.get(position);
                LayoutInflater inflater = ((Activity) this.getContext())
                        .getLayoutInflater();
                holder = new ViewHolder();
                rowView = inflater
                        .inflate(R.layout.foodlistactivity_item, null);
                holder.mNameText = (TextView) rowView
                        .findViewById(R.id.foodItemUsername);
                holder.mPhoto = (ImageView) rowView
                        .findViewById(R.id.foodItemPic);
                rowView.setTag(holder);

                holder.mNameText.setText(user.Name);

                if (!holder.mPhoto.isDrawingCacheEnabled()) {
                    holder.mPhoto.setTag(user.Pic);
                    new downImageTask().execute(holder.mPhoto);
                    holder.mPhoto.setDrawingCacheEnabled(true);
                }
                viewMap.put(position, rowView);
            } else {
                holder = (ViewHolder) rowView.getTag();
            }

            return rowView;
        }

        public class ViewHolder {
            public TextView mNameText;
            public ImageView mPhoto;
        }

    }

    public void setLoadingLayout() {
        LinearLayout layout = new LinearLayout(this);
        layout.setOrientation(LinearLayout.HORIZONTAL);
        ProgressBar progressBar = new ProgressBar(this);        progressBar.setPadding(0, 0, 15, 0);        layout.addView(progressBar);        TextView textView = new TextView(this);        textView.setText("加载中...");        textView.setGravity(Gravity.CENTER_VERTICAL);        layout.addView(textView);        layout.setGravity(Gravity.CENTER);        loadingLayout = new LinearLayout(this);        loadingLayout.addView(layout);        loadingLayout.setGravity(Gravity.CENTER);    }        private class scrollListener implements OnScrollListener {        @Override        public void onScroll(AbsListView view, int firstVisibleItem,                int visibleItemCount, int totalItemCount) {            // 当listView中没有数据，或者数据超过100条，或者不是10的整数倍（即数据不足）时隐藏“更多”并取消onScroll事件的绑定            if (mMyAdapter.getCount() >= 100 || mMyAdapter.getCount() % 10 > 0                    || mMyAdapter.getCount() == 0) {                listView.removeFooterView(loadingLayout);                listView.setOnScrollListener(null);            }            lastItem = firstVisibleItem + visibleItemCount - 1;// 这里减一是因为有FootView        }        @Override        public void onScrollStateChanged(AbsListView view, int scrollState) {            if (lastItem == mMyAdapter.getCount()                    && scrollState == OnScrollListener.SCROLL_STATE_IDLE) {                // 进行翻页操作                new scrollTask().execute(null);            }        }    }        public class readTask extends AsyncTask<Object, Void, Void> {            @Override        protected Void doInBackground(Object... arg0) {            users = new stringGetJson().getJson();            return null;        }        @Override        protected void onPostExecute(Void result) {            listView.addFooterView(loadingLayout);                        mMyAdapter = new MyAdapter(stringListActivity.this, users);            setListAdapter(mMyAdapter);            listView.setOnScrollListener(new scrollListener());        }    }    public class scrollTask extends AsyncTask<Object, Void, Void> {                @Override        protected Void doInBackground(Object... arg0) {            for (Iterator iterator = new stringGetJson().getJson()                    .iterator(); iterator.hasNext();) {                User user = (User) iterator.next();                users.add(user);            }            return null;        }        @Override        protected void onPostExecute(Void result) {            mMyAdapter.notifyDataSetChanged();        }    }}


Json数据来源（这里的例子中把json字符串直接写在代码中了，实际项目中需要改成从网络读取，例子中已经使用了多线程）：

package COM.Example.Main;

import java.lang.reflect.Type;
import java.util.Iterator;
import java.util.LinkedList;

import android.database.MatrixCursor;
import android.widget.ListView;
import android.widget.TextView;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
public class stringGetJson {
    
    // 设置临时ID，在项目中将被现实的id取代
    private int id = 0;
    
    public stringGetJson() {
        super();
    }

    //通过getJson方法从Json字符串获取User的列表
    public LinkedList<User> getJson() {
        String jsonData = "[{\"Name\":\"xinuxForJson1\",\"Pic\":\"http://www.qqjay.com/uploads/110414/1_234626_5.jpg\"},{\"Name\":\"xinuxForJson2\",\"Pic\":\"http://www.qqjay.com/uploads/110414/1_234626_3.jpg\"},{\"Name\":\"xinuxForJson3\",\"Pic\":\"http://www.qqjay.com/uploads/110414/1_234626_4.jpg\"},{\"Name\":\"xinuxForJson4\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian1/8.jpg\"},{\"Name\":\"xinuxForJson5\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian1/10.jpg\"},{\"Name\":\"xinuxForJson6\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian1/7.jpg\"},{\"Name\":\"xinuxForJson7\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian1/11.jpg\"},{\"Name\":\"xinuxForJson8\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian1/12.jpg\"},{\"Name\":\"xinuxForJson9\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian1/9.jpg\"},{\"Name\":\"xinuxForJson10\",\"Pic\":\"http://sucai.qqjay.com/fengmian/201104/tupian/7.jpg\"}]";
        Type listType = new TypeToken<LinkedList<User>>() {}.getType();
        Gson gson = new Gson();
        LinkedList<User> users = gson.fromJson(jsonData, listType);
        return users;
    }

    //为getJson提供了数据实体类
    final static class User {
        public String Name;
        public String Pic;
    }
}

图片下载AsyncTask

 

package COM.Example.Main;

import COM.Example.FunctionUtility.Download;
import android.graphics.Bitmap;
import android.os.AsyncTask;
import android.widget.ImageView;

public class downImageTask extends AsyncTask<ImageView, Void, Bitmap> {
    
    ImageView gView = null;
    @Override
    protected Bitmap doInBackground(ImageView... arg0) {
        gView = (ImageView)arg0[0];
        return Download.getBitmapFromUrl(gView.getTag().toString());
    }

    @Override
    protected void onPostExecute(Bitmap result) {
        if(result != null){
        this.gView.setImageBitmap(result);
        }
        this.gView = null;
    }
}

网络图片下载类：

 

package COM.Example.FunctionUtility;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

public class Download {
    public static Bitmap getBitmapFromUrl(String imgUrl) {
        URL url;
        Bitmap bitmap = null;
        try {
            url = new URL(imgUrl);
            InputStream is = url.openConnection().getInputStream();
            BufferedInputStream bis = new BufferedInputStream(is);
            bitmap = BitmapFactory.decodeStream(bis);
            bis.close();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return bitmap;
    }
}
转自：http://www.cnblogs.com/yeagen/archive/2011/04/19/2020985.html


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