android Gallery实现异步加载网络图片 并只加载当前停止页面图

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

1. import java.util.ArrayList;
   
2. import java.util.HashMap;
   
3. import java.util.List;
   
4. import android.app.Activity;
   
5. import android.graphics.Bitmap;
   
6. import android.graphics.BitmapFactory;
   
7. import android.os.AsyncTask;
   
8. import android.os.Bundle;
   
9. import android.os.Handler;
   
10. import android.os.Message;
    
11. import android.util.Log;
    
12. import android.view.KeyEvent;
    
13. import android.view.View;
    
14. import android.widget.AdapterView;
    
15. import android.widget.AdapterView.OnItemClickListener;
    
16. import android.widget.AdapterView.OnItemSelectedListener;
    
17. import android.widget.Gallery;
    
18. public class MyActivity extends Activity implements OnItemClickListener{
    
19. public static HashMap<String,Bitmap> imagesCache=new HashMap<String, Bitmap>(); //图片缓存
    
20. private Gallery images_ga;
    
21. public static ImageAdapter imageAdapter;
    
22. private int num=0;
    
23. List<String> urls = new ArrayList<String>(); //所有图片地址List
    
24. List<String> url = new ArrayList<String>(); //需要下载图片的url地址
    
25. 
    
26. @Override
    
27. protected void onCreate(Bundle savedInstanceState) {
    
28. 
    
29. super.onCreate(savedInstanceState);
    
30. setContentView(R.layout.gallery_1);
    
31. Files.mkdir(this);
    
32. init();
    
33. }
    
34. private void init(){
    
35. Bitmap image= BitmapFactory.decodeResource(getResources(),R.drawable.default_movie_post);
    
36. imagesCache.put("background_non_load",image); //设置缓存中默认的图片
    
37. images_ga = (Gallery) findViewById(R.id.gallery);
    
38. urls.add("http://hiphotos.baidu.com/baidu/pic/item/f603918fa0ec08fabf7a641659ee3d6d55fbda0d.jpg");
    
39. urls.add("http://hiphotos.baidu.com/baidu/pic/item/43a7d933c895d143d011bf9273f082025aaf071f.jpg");
    
40. urls.add("http://hiphotos.baidu.com/baidu/pic/item/63d0f703918fa0ec2ebf584b269759ee3d6ddb7f.jpg");
    
41. urls.add("http://hiphotos.baidu.com/baidu/pic/item/5ab5c9ea15ce36d31ed8387f3af33a87e850b1a5.jpg");
    
42. urls.add("http://hiphotos.baidu.com/baidu/pic/item/8601a18b87d6277f6e46217628381f30e924fc2c.jpg");
    
43. urls.add("http://hiphotos.baidu.com/baidu/pic/item/b48f8c54acf9964c3a29350e.jpg");
    
44. urls.add("http://hiphotos.baidu.com/baidu/pic/item/bd3eb13533fa828b48da6aabfd1f4134960a5af9.jpg");
    
45. urls.add("http://hiphotos.baidu.com/baidu/pic/item/29381f30e924b899da3ce5706e061d950a7bf672.jpg");
    
46. urls.add("http://hiphotos.baidu.com/baidu/pic/item/bd3eb13533fa828b48da6aabfd1f4134960a5af9.jpg");
    
47. urls.add("http://hiphotos.baidu.com/baidu/pic/item/4bed2e738bd4b31cd73d63fd87d6277f9e2ff877.jpg");
    
48. urls.add("http://hiphotos.baidu.com/baidu/pic/item/caef76094b36acaf92b619b87cd98d1001e99c24.jpg");
    
49. urls.add("http://hiphotos.baidu.com/baidu/pic/item/8435e5dde71190efd6154d95ce1b9d16fcfa608a.jpg");
    
50. urls.add("http://hiphotos.baidu.com/baidu/pic/item/b3de9c824ba1d4cd6d81190f.jpg");
    
51. urls.add("http://hiphotos.baidu.com/baidu/pic/item/e0fe9925cc2c683834a80f11.jpg");
    
52. urls.add("http://hiphotos.baidu.com/baidu/pic/item/0bd162d9f2d3572c65911a988a13632762d0c307.jpg");
    
53. urls.add("http://hiphotos.baidu.com/baidu/pic/item/ac6eddc451da81cb2ac1708a5266d01609243155.jpg");
    
54. 
    
55. urls.add("http://hiphotos.baidu.com/baidu/pic/item/1bd5ad6e8416d98080cb4a48.jpg");
    
56. urls.add("http://hiphotos.baidu.com/baidu/pic/item/3c6d55fbb2fb43169d0508ca20a4462309f7d36c.jpg");
    
57. urls.add("http://hiphotos.baidu.com/baidu/pic/item/faedab64034f78f0daf3664a79310a55b2191c8a.jpg");
    
58. urls.add("http://hiphotos.baidu.com/baidu/pic/item/2fdda3cc7cd98d10b05af088213fb80e7aec90f9.jpg");
    
59. urls.add("http://hiphotos.baidu.com/baidu/pic/item/b8014a90f603738d9536f39bb31bb051f819ec0f.jpg");
    
60. urls.add("http://hiphotos.baidu.com/baidu/pic/item/2fdda3cc7cd98d10b05af088213fb80e7aec90f9.jpg");
    
61. imageAdapter = new ImageAdapter(urls, this);
    
62. images_ga.setAdapter(imageAdapter);
    
63. images_ga.setOnItemClickListener(this);
    
64. images_ga.setOnItemSelectedListener(new OnItemSelectedListener() {
    
65. @Override
    
66. public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
    
67. num=arg2;
    
68. Log.i("mahua", "ItemSelected=="+arg2);
    
69. GalleryWhetherStop();
    
70. }
    
71. @Override
    
72. public void onNothingSelected(AdapterView<?> arg0) {
    
73. // TODO Auto-generated method stub
    
74. 
    
75. }
    
76. });
    
77. }
    
78. 
    
79. 
    
80. @Override
    
81. public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
    
82. Log.i("GOLF", "第"+arg2+"个被点击了");
    
83. }
    
84. 
    
85. /**
    
86. * 判断Gallery滚动是否停止,如果停止则加载当前页面的图片
    
87. */
    
88. private void GalleryWhetherStop() {
    
89. Runnable runnable = new Runnable() {
    
90. public void run() {
    
91. try {
    
92. int index =0;
    
93. index = num;
    
94. Thread.sleep(1000);
    
95. if (index == num) {
    
96. url.add(urls.get(num));
    
97. if(num!=0 && urls.get(num-1)!=null) {
    
98. url.add(urls.get(num-1));
    
99. }
    
100. if(num!=urls.size()-1 && urls.get(num+1)!=null) {
     
101. url.add(urls.get(num+1));
     
102. }
     
103. Message m = new Message();
     
104. m.what = 1;
     
105. mHandler.sendMessage(m);
     
106. }
     
107. } catch (Exception e) {
     
108. e.printStackTrace();
     
109. }
     
110. }
     
111. };
     
112. new Thread(runnable).start();
     
113. }
     
114. 
     
115. 
     
116. // 加载图片的异步任务
     
117. class LoadImageTask extends AsyncTask<String, Void, Bitmap> {
     
118. @Override 
     
119. protected void onCancelled() { 
     
120. // TODO Auto-generated method stub 
     
121. super.onCancelled(); 
     
122. } 
     
123. @Override 
     
124. protected void onPostExecute(Bitmap result) { 
     
125. // TODO Auto-generated method stub 
     
126. super.onPostExecute(result); 
     
127. } 
     
128. 
     
129. @Override
     
130. protected Bitmap doInBackground(String... params) {
     
131. Bitmap bitmap = null;
     
132. try {
     
133. String url = params[0];
     
134. 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
     
135. if (isExists == false) {//如果不存在就去下载图片
     
136. Net net = new Net();
     
137. byte[] data = net.downloadResource(MyActivity.this, url);
     
138. bitmap = BitmapFactory
     
139. .decodeByteArray(data, 0, data.length);
     
140. imagesCache.put(url, bitmap); // 把下载好的图片保存到缓存中
     
141. Files.saveImage(url, data);
     
142. } else {//如果存在直接读取缓存图片
     
143. byte[] data = Files.readImage(url);
     
144. bitmap = BitmapFactory
     
145. .decodeByteArray(data, 0, data.length);
     
146. imagesCache.put(url, bitmap); // 把下载好的图片保存到缓存中
     
147. }
     
148. Message m = new Message();//图片加载完成通知重新加载
     
149. m.what = 0;
     
150. mHandler.sendMessage(m);
     
151. } catch (Exception e) {
     
152. e.printStackTrace();
     
153. }
     
154. return bitmap;
     
155. }
     
156. 
     
157. }
     
158. 
     
159. 
     
160. private Handler mHandler = new Handler() {
     
161. public void handleMessage(Message msg) {
     
162. try {
     
163. switch (msg.what) {
     
164. case 0: {
     
165. imageAdapter.notifyDataSetChanged();
     
166. break;
     
167. }
     
168. case 1: {
     
169. for(int i=0; i<url.size(); i++) {
     
170. LoadImageTask task = new LoadImageTask();//异步加载图片
     
171. task.execute(url.get(i));
     
172. Log.i("mahua", url.get(i));
     
173. }
     
174. url.clear();
     
175. }
     
176. }
     
177. super.handleMessage(msg);
     
178. } catch (Exception e) {
     
179. e.printStackTrace();
     
180. }
     
181. }
     
182. };
     
183. @Override
     
184. public boolean onKeyDown(int keyCode, KeyEvent event) {
     
185. if(keyCode==KeyEvent.KEYCODE_BACK){
     
186. System.exit(0);
     
187. }
     
188. return super.onKeyDown(keyCode, event);
     
189. }
     
190. }

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1. import java.util.List;
   
2. import android.content.Context;
   
3. import android.content.res.AssetManager;
   
4. import android.content.res.TypedArray;
   
5. import android.graphics.Bitmap;
   
6. import android.view.View;
   
7. import android.view.ViewGroup;
   
8. import android.widget.BaseAdapter;
   
9. import android.widget.Gallery;
   
10. import android.widget.ImageView;
    
11. 
    
12. public class ImageAdapter extends BaseAdapter {
    
13. public static final BaseAdapter Adapter = null;
    
14. private List<String> imageUrls; // 图片地址list
    
15. private Context context;
    
16. int mGalleryItemBackground;
    
17. 
    
18. public ImageAdapter(List<String> imageUrls, Context context) {
    
19. this.imageUrls = imageUrls;
    
20. this.context = context;
    
21. // /*
    
22. // * 使用在res/values/attrs.xml中的<declare-styleable>定义 的Gallery属性.
    
23. // */
    
24. TypedArray a = context.obtainStyledAttributes(R.styleable.Gallery1);
    
25. /* 取得Gallery属性的Index id */
    
26. mGalleryItemBackground = a.getResourceId(
    
27. R.styleable.Gallery1_android_galleryItemBackground, 0);
    
28. /* 让对象的styleable属性能够反复使用 */
    
29. a.recycle();
    
30. }
    
31. public int getCount() {
    
32. return imageUrls.size();
    
33. }
    
34. public Object getItem(int position) {
    
35. return imageUrls.get(position);
    
36. }
    
37. public long getItemId(int position) {
    
38. return position;
    
39. }
    
40. public View getView(int position, View convertView, ViewGroup parent) {
    
41. Bitmap image;
    
42. ImageView view = new ImageView(context);
    
43. image = MyActivity.imagesCache.get(imageUrls.get(position));
    
44. // 从缓存中读取图片
    
45. if (image == null) {
    
46. image = MyActivity.imagesCache.get("background_non_load");
    
47. }
    
48. // 设置所有图片的资源地址
    
49. view.setImageBitmap(image);
    
50. view.setScaleType(ImageView.ScaleType.FIT_XY);
    
51. view.setLayoutParams(new Gallery.LayoutParams(240, 320));
    
52. view.setBackgroundResource(mGalleryItemBackground);
    
53. /* 设置Gallery背景图 */
    
54. return view;
    
55. }
    
56. }

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attrs.xml

1. <?xml version="1.0" encoding="utf-8"?>
   
2. <resources>
   
3. <declare-styleable name="TogglePrefAttrs">
   
4. <attr name="android:preferenceLayoutChild" />
   
5. </declare-styleable>
   
6. 
   
7. <!-- These are the attributes that we want to retrieve from the theme
   
8. in view/Gallery1.java -->
   
9. <declare-styleable name="Gallery1">
   
10. <attr name="android:galleryItemBackground" />
    
11. </declare-styleable>
    
12. 
    
13. <declare-styleable name="LabelView">
    
14. <attr name="text" format="string" />
    
15. <attr name="textColor" format="color" />
    
16. <attr name="textSize" format="dimension" />
    
17. </declare-styleable>
    
18. </resources>

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