Android 利用 AsyncTask 异步读取网络图片

1.新建Android工程AsyncLoadPicture

新建布局文件activity_main.xml主界面为一个GridView，还有其子项布局文件gridview_item.xml

2.功能主界面MainActivity.java,主代码如下

package com.example.asyncloadpicture;

import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.GridView;

/**
 * @author ymw
 * @data 2014-12-03
 */
public class MainActivity extends Activity {

    private GridView gridViewImg;
    private ArrayList<ImageEntity> imageList = new ArrayList<ImageEntity>();

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

        gridViewImg = (GridView) findViewById(R.id.gridViewImg);
        initData();
    }

    private void initData() {
        for (int i = 0; i < 15; i++) {
            ImageEntity b = new ImageEntity();
            b.setImage(BitmapFactory.decodeResource(getResources(),
                    R.drawable.nopicture));

            imageList.add(b);
        }

        ImageAdapter adapter = new ImageAdapter(getApplicationContext(),
                imageList);
        gridViewImg.setAdapter(adapter);
        String[] params = {
                "https://images0.cnblogs.com/i/169207/201408/112229149526951.png",
                "p2" };
        new ImageLoadTask(getApplicationContext(), adapter).execute(params);
    }

    /** 图片异步加载类 */
    public class ImageLoadTask extends AsyncTask<String, Void, Void> {
        private ImageAdapter adapter;

        public ImageLoadTask(Context context, ImageAdapter adapter) {
            this.adapter = adapter;
        }

        @Override
        protected Void doInBackground(String... params) {
            String url = params[0];// 获取传来的参数，图片uri地址
            String p2 = params[1];
            for (int i = 0; i < adapter.getCount(); i++) {
                ImageEntity bean = (ImageEntity) adapter.getItem(i);
                Bitmap bitmap = BitmapFactory.decodeStream(Request
                        .HandlerData(url));
                bean.setImage(bitmap);
                publishProgress(); // 通知去更新UI
            }

            return null;
        }

        public void onProgressUpdate(Void... voids) {
            if (isCancelled())
                return;
            // 更新UI
            adapter.notifyDataSetChanged();
        }
    }

    /** 图片实体 */
    public class ImageEntity {
        private Bitmap image;

        public Bitmap getImage() {
            return image;
        }

        public void setImage(Bitmap image) {
            this.image = image;
        }

    }
}

3.GridView列表图片适配器代码ImageAdapter.java

package com.example.asyncloadpicture;

import java.util.ArrayList;

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 com.example.asyncloadpicture.MainActivity.ImageEntity;

/**
 * 
 * @author ymw
 * @data 2014-12-03 图片适配器
 */
public class ImageAdapter extends BaseAdapter {

    private Context _context;
    private ArrayList<ImageEntity> _list;

    public ImageAdapter(Context context, ArrayList<ImageEntity> imageList) {
        this._context = context;
        this._list = imageList;
    }

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

    @Override
    public Object getItem(int position) {
        return _list.get(position);
    }

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = LayoutInflater.from(_context);
        convertView = inflater.inflate(R.layout.gridview_item, null);

        ImageView imgView = (ImageView) convertView.findViewById(R.id.imgView);
        ImageEntity b = _list.get(position);
        // 如果有图片则读取，没有则跳过
        if (b.getImage() != null) {
            imgView.setImageBitmap(b.getImage());
        }
        return convertView;
    }
}

4.请求网络读取图片的类Request.java

package com.example.asyncloadpicture;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;

import android.graphics.drawable.Drawable;
import android.util.Log;

/**
 * 工具类，主要根据url读取图片返回流的方法
 * 
 * @author ymw
 * 
 */
public class Request {
    public static InputStream HandlerData(String url) {
        InputStream inStream = null;

        try {
            URL feedUrl = new URL(url);
            URLConnection conn = feedUrl.openConnection();
            conn.setConnectTimeout(10 * 1000);
            inStream = conn.getInputStream();
        } catch (Exception e) {
            e.printStackTrace();
        }

        return inStream;
    }

    /** 直接返回Drawable对象设置图片 */
    public static Drawable loadImageFromNetwork(String imageUrl) {
        Drawable drawable = null;
        try {
            // 可以在这里通过文件名来判断，是否本地有此图片
            drawable = Drawable.createFromStream(
                    new URL(imageUrl).openStream(), "image.jpg");
        } catch (IOException e) {
            Log.d("test", e.getMessage());
        }
        if (drawable == null) {
            Log.d("test", "null drawable");
        } else {
            Log.d("test", "not null drawable");
        }

        return drawable;
    }
}

5.代码实例如下链接：

http://files.cnblogs.com/_ymw/AsyncLoadPicture_%E5%8D%9A%E5%AE%A2%E9%99%84%E4%BB%B6.rar