android Gallery实现异步加载网络图片

最新推荐文章于 2022-04-02 14:11:12 发布

iteye_264

最新推荐文章于 2022-04-02 14:11:12 发布

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文章标签：移动开发 java

本文介绍了一个实现动态图片加载与缓存优化的方法，通过在Gallery滑动时仅加载当前页面图片，并利用缓存减少加载次数，提高用户体验。

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之前在网上找了很多都没有这方面的资料，大概的效果是当Gallery滑动时不下载图片，当Gallery滑动停止时加载当前页面图片，自己花了一点时间大概的实现了，如果各位有更好的意见欢迎说出来大家一起学习。
先上图看看效果：
这图是在加载图片时显示的默认图片，当图片加载完成则替换。

图片加载完成效果图

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.KeyEvent;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.Gallery;
public class MyActivity extends Activity implements OnItemClickListener{
    public static HashMap<String,Bitmap> imagesCache=new HashMap<String, Bitmap>(); //图片缓存
    private Gallery images_ga;
    public static ImageAdapter imageAdapter;
    private int num=0;
    List<String> urls = new ArrayList<String>(); //所有图片地址List
    List<String> url = new ArrayList<String>(); //需要下载图片的url地址
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.gallery_1);
        Files.mkdir(this);
        init();
    }
    private void init(){
        Bitmap image= BitmapFactory.decodeResource(getResources(),R.drawable.default_movie_post);
        imagesCache.put("background_non_load",image);       //设置缓存中默认的图片
        images_ga = (Gallery) findViewById(R.id.gallery);
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/f603918fa0ec08fabf7a641659ee3d6d55fbda0d.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/43a7d933c895d143d011bf9273f082025aaf071f.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/63d0f703918fa0ec2ebf584b269759ee3d6ddb7f.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/5ab5c9ea15ce36d31ed8387f3af33a87e850b1a5.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/8601a18b87d6277f6e46217628381f30e924fc2c.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/b48f8c54acf9964c3a29350e.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/bd3eb13533fa828b48da6aabfd1f4134960a5af9.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/29381f30e924b899da3ce5706e061d950a7bf672.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/bd3eb13533fa828b48da6aabfd1f4134960a5af9.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/4bed2e738bd4b31cd73d63fd87d6277f9e2ff877.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/caef76094b36acaf92b619b87cd98d1001e99c24.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/8435e5dde71190efd6154d95ce1b9d16fcfa608a.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/b3de9c824ba1d4cd6d81190f.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/e0fe9925cc2c683834a80f11.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/0bd162d9f2d3572c65911a988a13632762d0c307.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/ac6eddc451da81cb2ac1708a5266d01609243155.jpg");
        
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/1bd5ad6e8416d98080cb4a48.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/3c6d55fbb2fb43169d0508ca20a4462309f7d36c.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/faedab64034f78f0daf3664a79310a55b2191c8a.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/2fdda3cc7cd98d10b05af088213fb80e7aec90f9.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/b8014a90f603738d9536f39bb31bb051f819ec0f.jpg");
        urls.add("http://hiphotos.baidu.com/baidu/pic/item/2fdda3cc7cd98d10b05af088213fb80e7aec90f9.jpg");
        imageAdapter = new ImageAdapter(urls, this);
        images_ga.setAdapter(imageAdapter);
        images_ga.setOnItemClickListener(this);
        images_ga.setOnItemSelectedListener(new OnItemSelectedListener() {
   @Override
   public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
    num=arg2;
    Log.i("mahua", "ItemSelected=="+arg2);
    GalleryWhetherStop();
   }
   @Override
   public void onNothingSelected(AdapterView<?> arg0) {
    // TODO Auto-generated method stub
    
   }
  });
    }
    
    
    @Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
     Log.i("GOLF", "第"+arg2+"个被点击了");
}
    
    /**
     * 判断Gallery滚动是否停止,如果停止则加载当前页面的图片
     */
    private void GalleryWhetherStop() {
  Runnable runnable = new Runnable() {
   public void run() {
    try {
     int index =0;
      index = num;
      Thread.sleep(1000);
      if (index == num) {
       url.add(urls.get(num));
       if(num!=0 && urls.get(num-1)!=null) {
        url.add(urls.get(num-1));
       }
       if(num!=urls.size()-1 && urls.get(num+1)!=null) {
        url.add(urls.get(num+1));
       }
       Message m = new Message();
       m.what = 1;
       mHandler.sendMessage(m);
      }
    } catch (Exception e) {
     e.printStackTrace();
    }
   }
  };
  new Thread(runnable).start();
}
    
    
// 加载图片的异步任务
  class LoadImageTask extends AsyncTask<String, Void, Bitmap> {
   @Override  
        protected void onCancelled() {  
            // TODO Auto-generated method stub  
            super.onCancelled();  
        }  
    @Override  
         protected void onPostExecute(Bitmap result) {  
             // TODO Auto-generated method stub        
             super.onPostExecute(result);  
         }  
   
  @Override
  protected Bitmap doInBackground(String... params) {
   Bitmap bitmap = null;
   try {
    String url = params[0];
    boolean isExists = Files.compare(url); //这里是自己写的工具类，判断本地缓存是否已经下载过图片
    if (isExists == false) {//如果不存在就去下载图片
     Net net = new Net();
     byte[] data = net.downloadResource(MyActivity.this, url);
     bitmap = BitmapFactory
       .decodeByteArray(data, 0, data.length);
     imagesCache.put(url, bitmap); // 把下载好的图片保存到缓存中
     Files.saveImage(url, data);
    } else {//如果存在直接读取缓存图片
     byte[] data = Files.readImage(url);
     bitmap = BitmapFactory
       .decodeByteArray(data, 0, data.length);
     imagesCache.put(url, bitmap); // 把下载好的图片保存到缓存中
    }
    Message m = new Message();//图片加载完成通知重新加载
    m.what = 0;
    mHandler.sendMessage(m);
   } catch (Exception e) {
    e.printStackTrace();
   }
   return bitmap;
  }
   
  }
    
    
  private Handler mHandler = new Handler() {
  public void handleMessage(Message msg) {
   try {
    switch (msg.what) {
     case 0: {
      imageAdapter.notifyDataSetChanged();
      break;
     }
     case 1: {
      for(int i=0; i<url.size(); i++) {
       LoadImageTask task = new LoadImageTask();//异步加载图片
       task.execute(url.get(i));
       Log.i("mahua", url.get(i));
      }
      url.clear();
     }
    }
    super.handleMessage(msg);
   } catch (Exception e) {
    e.printStackTrace();
   }
  }
};
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
  if(keyCode==KeyEvent.KEYCODE_BACK){
   System.exit(0);
  }
  return super.onKeyDown(keyCode, event);
}
}


import java.util.List;
import android.content.Context;
import android.content.res.AssetManager;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;

public class ImageAdapter extends BaseAdapter {
public static final BaseAdapter Adapter = null;
private List<String> imageUrls; // 图片地址list
private Context context;
int mGalleryItemBackground;

public ImageAdapter(List<String> imageUrls, Context context) {
this.imageUrls = imageUrls;
this.context = context;
// /*
// * 使用在res/values/attrs.xml中的<declare-styleable>定义 的Gallery属性.
// */
TypedArray a = context.obtainStyledAttributes(R.styleable.Gallery1);
/* 取得Gallery属性的Index id */
mGalleryItemBackground = a.getResourceId(
R.styleable.Gallery1_android_galleryItemBackground, 0);
/* 让对象的styleable属性能够反复使用 */
a.recycle();
}
public int getCount() {
return imageUrls.size();
}
public Object getItem(int position) {
return imageUrls.get(position);
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
Bitmap image;
ImageView view = new ImageView(context);
image = MyActivity.imagesCache.get(imageUrls.get(position));
// 从缓存中读取图片
if (image == null) {
image = MyActivity.imagesCache.get("background_non_load");
}
// 设置所有图片的资源地址
view.setImageBitmap(image);
view.setScaleType(ImageView.ScaleType.FIT_XY);
view.setLayoutParams(new Gallery.LayoutParams(240, 320));
view.setBackgroundResource(mGalleryItemBackground);
/* 设置Gallery背景图 */
return view;
}
}


attrs.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="TogglePrefAttrs">
<attr name="android:preferenceLayoutChild" />
</declare-styleable>

<!-- These are the attributes that we want to retrieve from the theme
in view/Gallery1.java -->
<declare-styleable name="Gallery1">
<attr name="android:galleryItemBackground" />
</declare-styleable>

<declare-styleable name="LabelView">
<attr name="text" format="string" />
<attr name="textColor" format="color" />
<attr name="textSize" format="dimension" />
</declare-styleable>
</resources>

主要的结构就这样了，下载文件和文件保存自己随便写写就行了。如有更好的建议欢迎提出了，大家一起分享学习。