[android] 练习使用ListView（二）

主要练习异步任务和LruCache缓存

package com.android.test;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

import com.nostra13.universalimageloader.core.ImageLoader;
import com.nostra13.universalimageloader.core.ImageLoaderConfiguration;
import com.nostra13.universalimageloader.core.assist.FailReason;
import com.nostra13.universalimageloader.core.listener.ImageLoadingListener;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.BitmapDrawable;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.util.LruCache;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;

public class MainActivity extends Activity {
    private ListView lv_images;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        lv_images = (ListView) findViewById(R.id.lv_images);
        
        ImageLoaderConfiguration configuration=ImageLoaderConfiguration.createDefault(this);
        ImageLoader.getInstance().init(configuration);
        
        ListAdapter adapter = new ImageAdapter();
        lv_images.setAdapter(adapter);
    }
    /**
     * 适配器
     * @author taoshihan
     *
     */
    class ImageAdapter extends BaseAdapter {
        private LruCache<String, BitmapDrawable> mImageCache;
        public ImageAdapter() {
            int maxSize=(int) (Runtime.getRuntime().maxMemory()/8);
            mImageCache=new LruCache<String, BitmapDrawable>(maxSize){
                protected int sizeOf(String key, BitmapDrawable drawable) {
                    return drawable.getBitmap().getByteCount(); 
                };
            };
        }
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            String url=(String) getItem(position);
            View view;
            if(convertView!=null){
                view=convertView;
            }else{
                view=View.inflate(getApplicationContext(), R.layout.image_item, null);
            }
            ImageView imageView=(ImageView) view.findViewById(R.id.tv_image);
            
            BitmapDrawable bitmapDrawable=getBitmapFromMemoryCache(url);
            if(bitmapDrawable!=null){
                //读取缓存图片
                imageView.setImageDrawable(bitmapDrawable);
            }else{
                //读取网络图片
                ImageWorkerTask task=new ImageWorkerTask(imageView);
                task.execute(url);
            }
            return view;
        }
        /**
         * 从缓存中读取图片
         * @param key
         * @return 
         */
        public BitmapDrawable getBitmapFromMemoryCache(String key) {
            if(mImageCache.get(key)!=null){
                return mImageCache.get(key);
            }
            return null;
        }
        public void addBitmapToMemoryCache(String key,BitmapDrawable drawable){
            if(getBitmapFromMemoryCache(key)==null){
                mImageCache.put(key, drawable);
            }
        }
        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return Images.IMAGE_URLS.length;
        }

        @Override
        public Object getItem(int position) {
            return Images.IMAGE_URLS[position];
        }

        @Override
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            return position;
        }
        /**
         * 异步任务
         * @author taoshihan
         *
         */
        class ImageWorkerTask extends AsyncTask<String, Void, BitmapDrawable>{
            private ImageView imageView;
            public ImageWorkerTask(ImageView imageView) {
                this.imageView=imageView;
            }
            @Override
            protected BitmapDrawable doInBackground(String... params) {
                String imageUrl=params[0];
                Bitmap bitmap=downLoadBitmap(imageUrl);
                BitmapDrawable drawable=new BitmapDrawable(getApplicationContext().getResources(),bitmap);
                addBitmapToMemoryCache(imageUrl, drawable);
                return drawable;
            }
            //下载图片
            private Bitmap downLoadBitmap(String imageUrl) {
                Bitmap bitmap=null;
                try {
                    URL url=new URL(imageUrl);
                    HttpURLConnection conn=(HttpURLConnection) url.openConnection();
                    conn.setConnectTimeout(10000);
                    InputStream is=conn.getInputStream();
                    bitmap=BitmapFactory.decodeStream(is);
                } catch (Exception e) {
                }
                return bitmap;
            }
            //下载完成的
            @Override
            protected void onPostExecute(BitmapDrawable result) {
                if(imageView!=null&&result!=null){
                    imageView.setImageDrawable(result);
                }
            }
            
        }

    }
    static class Images{
        public final static String[] IMAGE_URLS = new String[]{
            "http://img.my.csdn.net/uploads/201508/05/1438760758_3497.jpg",    
            "http://img.my.csdn.net/uploads/201508/05/1438760758_6667.jpg",  
            "http://img.my.csdn.net/uploads/201508/05/1438760757_3588.jpg",  
            "http://img.my.csdn.net/uploads/201508/05/1438760756_3304.jpg",  
            "http://img.my.csdn.net/uploads/201508/05/1438760755_6715.jpeg",  
            "http://img.my.csdn.net/uploads/201508/05/1438760726_5120.jpg",  
            "http://img.my.csdn.net/uploads/201508/05/1438760726_8364.jpg",  
            "http://img.my.csdn.net/uploads/201508/05/1438760725_4031.jpg",  
            "http://img.my.csdn.net/uploads/201508/05/1438760724_9463.jpg",  
            "http://img.my.csdn.net/uploads/201508/05/1438760724_2371.jpg",  
            "http://img.my.csdn.net/uploads/201508/05/1438760707_4653.jpg"
        };
    }
}