android Gallery實現非同步載入網狀圖片

之前在網上找了很多都沒有這方面的資料，大概的效果是當Gallery滑動時不下載圖片，當Gallery滑動停止時載入當前頁面圖片，自己花了一點時間大概的實現了，如果各位有更好的意見歡迎說出來大家一起學習。
先看看效果：
這圖是在載入圖片時顯示的預設圖片，當圖片載入完成則替換。

圖片載入完成

1. 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>(); //圖片緩衝    private Gallery images_ga;    public static ImageAdapter imageAdapter;    private int num=0;    List<String> urls = new ArrayList<String>(); //所有圖片地址List    List<String> url = new ArrayList<String>(); //需要下載圖片的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);       //設定緩衝中預設的圖片        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       }  });    }            @Overridepublic void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {     Log.i("GOLF", "第"+arg2+"個被點擊了");}        /**     * 判斷Gallery滾動是否停止,如果停止則載入當前頁面的圖片     */    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();}        // 載入圖片的非同步任務  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); //這裡是自己寫的工具類，判斷本機快取是否已經下載過圖片    if (isExists == false) {//如果不存在就去下載圖片     Net net = new Net();     byte[] data = net.downloadResource(MyActivity.this, url);     bitmap = BitmapFactory       .decodeByteArray(data, 0, data.length);     imagesCache.put(url, bitmap); // 把下載好的圖片儲存到緩衝中     Files.saveImage(url, data);    } else {//如果存在直接讀取緩衝圖片     byte[] data = Files.readImage(url);     bitmap = BitmapFactory       .decodeByteArray(data, 0, data.length);     imagesCache.put(url, bitmap); // 把下載好的圖片儲存到緩衝中    }    Message m = new Message();//圖片載入完成通知重新載入    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();//非同步載入圖片       task.execute(url.get(i));       Log.i("mahua", url.get(i));      }      url.clear();     }    }    super.handleMessage(msg);   } catch (Exception e) {    e.printStackTrace();   }  }};@Overridepublic 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; // 圖片地址listprivate 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>定義 的Gallery屬性.// */TypedArray a = context.obtainStyledAttributes(R.styleable.Gallery1);/* 取得Gallery屬性的Index id */mGalleryItemBackground = a.getResourceId(R.styleable.Gallery1_android_galleryItemBackground, 0);/* 讓對象的styleable屬效能夠反覆使用 */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));// 從緩衝中讀取圖片if (image == null) {image = MyActivity.imagesCache.get("background_non_load");}// 設定所有圖片的資源地址view.setImageBitmap(image);view.setScaleType(ImageView.ScaleType.FIT_XY);view.setLayoutParams(new Gallery.LayoutParams(240, 320));view.setBackgroundResource(mGalleryItemBackground);/* 設定Gallery背景圖 */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 themein 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>

主要的結構就這樣了，下載檔案和檔案儲存自己隨便寫寫就行了。如有更好的建議歡迎提出了，大家一起分享學習。