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[操作系统][android] 练习使用ListView(三)


解决OOM和图片乱序问题

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 ListView mListView;    private LruCache<String, BitmapDrawable> mImageCache;    public ImageAdapter() {      int maxSize=(int) (Runtime.getRuntime().maxMemory()/1024)/8;      mImageCache=new LruCache<String, BitmapDrawable>(maxSize){        protected int sizeOf(String key, BitmapDrawable drawable) {          return drawable.getBitmap().getByteCount()/1024;         };      };    }    @Override    public View getView(int position, View convertView, ViewGroup parent) {      //第三个参数就是ListView      if(mListView==null){        mListView=(ListView) 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);      //给ImageView设置标签      imageView.setTag(url);      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(mListView,url);        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(ListView parent,String imageUrl) {        //在ListView中通过标签找到ImageView控件        this.imageView=(ImageView) parent.findViewWithTag(imageUrl);      }      @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"    };  }}