【Android】加载网络图片-------转自1

转自：http://www.apkbus.com/android-51646-1-1.html 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); } } 复制代码 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; } } 复制代码 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> 复制代码 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。 最后应要求附上源码。  GallerySync.rar (172.86 KB, 下载次数: 391)