一.LruCache的简单介绍
- Cache保存一个强引用来限制内容数量，每当Item被访问的时候，此Item就会移动到队列的头部。
- * 当cache已满的时候加入新的item时，在队列尾部的item会被回收。
- * 如果你cache的某个值需要明确释放，重写entryRemoved()
- * 如果key相对应的item丢掉啦，重写create().这简化了调用代码，即使丢失了也总会返回。
- * is limited to 4MiB of bitmaps: 默认cache大小是测量的item的数量，重写sizeof计算不同item的
- * 大小。
二.使用Lrucache来异步加载图片，防止阻塞（缓存图片）
下面是我的一个小程序，使用得到了Lrucache，总共有三个类，代码注释也是很详细的，很适合初学者学习。主要的功能就是形成一个像瀑布的图片墙。
在第三个类中有这个项目的设计思想。大家可以看看，共同进步，谢谢！！！
第一个类
1 package com.pangzaifei.falls;
2
3 import android.app.Activity;
4 import android.os.Bundle;
5
6 /**
7 * 瀑布流
8 *
9 */
10 public class Demo extends Activity {
11 @Override
12 protected void onCreate(Bundle savedInstanceState) {
13 super.onCreate(savedInstanceState);
14 setContentView(R.layout.activity_demo);
15
16 }
17 }
第二个类
1 package com.pangzaifei.falls;
2
3 import android.graphics.Bitmap;
4 import android.graphics.BitmapFactory;
5 import android.graphics.BitmapFactory.Options;
6 import android.support.v4.util.LruCache;
7
8 /**
9 * 图片资源 数据源类
10 *
11 */
12 public class Images {
13 private static Images images;
14 // Cache保存一个强引用来限制内容数量，每当Item被访问的时候，此Item就会移动到队列的头部。
15 // 当cache已满的时候加入新的item时，在队列尾部的item会被回收。
16 // 如果你cache的某个值需要明确释放，重写entryRemoved()
17 // 如果key相对应的item丢掉啦，重写create().这简化了调用代码，即使丢失了也总会返回。
18 // 默认cache大小是测量的item的数量，重写sizeof计算不同item的大小。
19 private LruCache<String, Bitmap> mMemoryCache;
20
21 public Images() {
22 initLrucache();// 初始化lrucache
23 }
24
25 public static Images getInstance() {
26 if (images == null) {
27 images = new Images();
28 }
29 return images;
30 }
31
32 /**
33 * 初始化lrucache
34 */
35 private void initLrucache() {
36 // 获取应用程序最大内存
37 long maxSize = Runtime.getRuntime().maxMemory();
38 // 设置图片缓存大小为程序最大可用内存的1/8.
39 int cacheSize = (int) (maxSize / 8);
40 mMemoryCache = new LruCache<String, Bitmap>(cacheSize);
41 }
42
43 /**
44 * 从LruCache中获取一张图片，如果不存在就返回null 从lrucache中获得key key LruCache的键，传入图片的url地址
45 * return 对应传入的bitmap对象，或者null
46 */
47 public Bitmap getMemoryCache(String key) {
48 if (mMemoryCache != null) {
49 Bitmap bitmap = mMemoryCache.get(key);
50 if (bitmap != null) {
51 return bitmap;
52 }
53 }
54 return null;
55 }
56
57 /**
58 * 将图片添加到lrucache中
59 *
60 * @param key
61 * LruCache的键，这里传入图片的URL地址
62 * @param bitmap
63 * 这里指的是从网络上下载的bitmap对象。
64 */
65 public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
66 if (getMemoryCache(key) == null) {
67 mMemoryCache.put(key, bitmap);
68 }
69 }
70
71 public static final String[] imageThumbs = new String[] {
72 "http://img.my.csdn.net/uploads/201309/01/1378037235_3453.jpg",
73 "http://img.my.csdn.net/uploads/201309/01/1378037235_7476.jpg",
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276 "http://img.my.csdn.net/uploads/201308/31/1377949454_6367.jpg" };
277
278 /**
279 * 将大图缩放
280 *
281 * @param path
282 * @param mClolumnWidth
283 */
284 public Bitmap decodeSimpleBitMapFromResource(String path, int mClolumnWidth) {
285 //第一次解析将inJustDecodeBounds设置为true，来获取图片的大小
286 final Options options = new Options();
287 options.inJustDecodeBounds = true;
288 Bitmap bitmap = BitmapFactory.decodeFile(path, options);
289 //调用方法计算insampleSize的值
290 options.inSampleSize = decodeSimpleSize(options, mClolumnWidth);
291 //使用获取到的inSampleSize的值
292 options.inJustDecodeBounds = false;
293 return BitmapFactory.decodeFile(path, options);
294
295 }
296
297 /**
298 * 获得simpleSize
299 *
300 * @param options
301 * @return
302 */
303 private int decodeSimpleSize(Options options, int reqwidth) {
304 //源图片的宽度
305 int width = options.outWidth;
306 int simplesize = 1;
307 if (width > reqwidth) {
308 //计算出实际宽度和目标宽度的比率
309 simplesize = Math.round(width / reqwidth);
310 }
311 return simplesize;
312 }
313 }
第三个类
1 package com.pangzaifei.falls;
2
3 import java.io.BufferedInputStream;
4 import java.io.BufferedOutputStream;
5 import java.io.File;
6 import java.io.FileOutputStream;
7 import java.io.IOException;
8 import java.io.InputStream;
9 import java.net.HttpURLConnection;
10 import java.net.URL;
11 import java.util.ArrayList;
12 import java.util.HashSet;
13 import java.util.List;
14 import java.util.Set;
15
16 import android.content.Context;
17 import android.graphics.Bitmap;
18 import android.graphics.BitmapFactory;
19 import android.os.AsyncTask;
20 import android.os.Environment;
21 import android.os.Handler;
22 import android.os.Message;
23 import android.util.AttributeSet;
24 import android.view.MotionEvent;
25 import android.view.View;
26 import android.view.View.OnTouchListener;
27 import android.widget.ImageView;
28 import android.widget.ImageView.ScaleType;
29 import android.widget.LinearLayout;
30 import android.widget.ScrollView;
31 import android.widget.Toast;
32
33 /**
34 * 瀑布流类 <主要用到了LruCache类，缓存图片 >
35 *
36 * 原理: 1：创建3个linearlayout，设置他们的宽度，将获得的图片压缩成和3个linearlayout一样的宽度，
37 * 然后根据3个linearlayout的高度来判断，将bitmap添加到哪一个linearlayout中
38 * 2：翻页处理，根据手势抬起的位置和滑动的末尾处来进行翻页
39 *
40 */
41 /*
42 ScrollView原理
43 视图的滚动过程，其实是在不断修改原点坐标。当手指触摸后，ScrollView会暂时拦截触摸事件，
44 使用一个计时器。假如在计时器到点后没有发生手指移动事件，那么ScrollView发送tracking events到被点击的subView；
45 若是在计时器到点后发生了移动事件，那么ScrollView取消tracking自己促发滚动。
46 */
47 /*首先还是讲一下实现原理，瀑布流的布局方式虽然看起来好像排列的很随意，其实它是有很科学的排列规则的。
48 * 整个界面会根据屏幕的宽度划分成等宽的若干列，由于手机的屏幕不是很大，这里我们就分成三列。每当需要添加一张图片时，
49 * 会将这张图片的宽度压缩成和列一样宽，再按照同样的压缩比例对图片的高度进行压缩，然后在这三列中找出当前高度最小的一列，
50 * 将图片添加到这一列中。之后每当需要添加一张新图片时，都去重复上面的操作，就会形成瀑布流格局的照片墙
51 */
52 public class PhotoFallScrollView extends ScrollView implements OnTouchListener {
53 /**
54 * 记录当前已加载到第几页
55 */
56 private static int page;
57 /**
58 * 每页显示多少张图片的数量
59 */
60 private static final int PAGE_SIZE = 8;
61 private Context mContext;
62 /**
63 * 数据源图片
64 */
65 private Images mImagesThoumb;
66 /**
67 * task请求集合
68 */
69 private Set<DownLoadTask> mTasks;
70 //判断是否是第一次进入
71 boolean isFirstEntr = true;
72
73 /**三列布局
74 *
75 */
76 private LinearLayout mFirstColumn;
77 private LinearLayout mSecondColumn;
78 private LinearLayout mThirdColumn;
79 //当前第一列，第二列，第三列的高度
80 private int mFirstColumnHeight;
81 private int mSecondColumnHeight;
82 private int mThirdColumnHeight;
83 /**
84 * 每一列的宽度
85 */
86 private int mClolumnWidth;
87
88 private long mDelay = 5;
89 /**
90 * 上次滑动的最后位置
91 */
92 private static int lastScrollY = -1;
93
94 /**
95 * 是否已加载过一次layout，这里onLayout中的初始化只需加载一次
96 */
97 private boolean loadOnce;
98 /**
99 * 存放图片的集合
100 */
101 private List<ImageView> mImageViewList = new ArrayList<ImageView>();
102
103 public PhotoFallScrollView(Context context, AttributeSet attrs, int defStyle) {
104 super(context, attrs, defStyle);
105 this.mContext = context;
106 init();
107 }
108
109 public PhotoFallScrollView(Context context, AttributeSet attrs) {
110 super(context, attrs);
111 this.mContext = context;
112 init();
113 }
114
115 public PhotoFallScrollView(Context context) {
116 super(context);
117 this.mContext = context;
118 init();
119 }
120
121 /**
122 * 初始化
123 */
124 private void init() {
125 mImagesThoumb = Images.getInstance();
126 mTasks = new HashSet<DownLoadTask>();
127 setOnTouchListener(this);
128 }
129
130 /**
131 * 进行一些关键性的初始化操作，获取MyScrollView的高度以及得到第一列的宽度值。
132 * 并在这里开始加载第一页的图片。
133 *
134 */
135 @Override
136 protected void onLayout(boolean changed, int l, int t, int r, int b) {
137 super.onLayout(changed, l, t, r, b);
138
139 // 第一次进入就加载第一页的图片
140 if (changed && !loadOnce) {
141 mScrollViewHeight = this.getHeight();
142 mScrollLayout = this.getChildAt(0);//从id的值为0处开始获取
143 mFirstColumn = (LinearLayout) findViewById(R.id.first_column);
144 mSecondColumn = (LinearLayout) findViewById(R.id.second_column);
145 mThirdColumn = (LinearLayout) findViewById(R.id.third_column);
146 //获取每一列的宽度
147 mClolumnWidth = mFirstColumn.getWidth();
148 loadOnce = true;
149 //开始加载下一页的图片
150 loadMoreImages();
151 }
152 }
153
154 /**开始加载下一页的图片，每张图片都会开启一个异步线程去下载。
155 * 加载图片
156 */
157 private void loadMoreImages() {
158 if (hashSdcard()) {
159
160 // 根据页数加载图片
161 int startIndex = page * PAGE_SIZE;
162 int endIndex = page * PAGE_SIZE + PAGE_SIZE;
163
164 if (startIndex < mImagesThoumb.imageThumbs.length) {
165 if (endIndex > mImagesThoumb.imageThumbs.length) {
166 endIndex = mImagesThoumb.imageThumbs.length;
167 }
168 for (int i = startIndex; i < endIndex; i++) {
169 String imageUrl = mImagesThoumb.imageThumbs[i].toString();
170 if (imageUrl != null && !"".equals(imageUrl)) {
171 //开始下载图片
172 downLoadData(imageUrl);
173 }
174 }
175 page++;
176 } else {
177 Toast.makeText(mContext, "没有更多图片了", 0).show();
178 }
179 } else {
180 Toast.makeText(mContext, "无sdcard", 0).show();
181 }
182 }
183
184 /**
185 * 下载
186 *
187 * @param imageUrl
188 */
189 private void downLoadData(String imageUrl) {
190 DownLoadTask task = new DownLoadTask();
191 mTasks.add(task);
192 //执行
193 task.execute(imageUrl);
194 }
195
196 /**
197 *异步下载图片
198 */
199 public class DownLoadTask extends AsyncTask<String, String, Bitmap> {
200 /**
201 * 图片的URL地址
202 */
203 private String mImageUrl;
204
205 @Override
206 protected Bitmap doInBackground(String... params) {
207 try {
208 mImageUrl = params[0];
209 Bitmap bitmapFromMemory = mImagesThoumb
210 .getMemoryCache(mImageUrl);
211 if (bitmapFromMemory != null) {
212 return bitmapFromMemory;
213 }
214 if (hashSdcard()) {
215 Bitmap bitmap = loadImage(mImageUrl);
216 return bitmap;
217 } else {
218 Toast.makeText(mContext, "无sdcard,无法获取图片", 0).show();
219 }
220
221 } catch (Exception e) {
222 e.printStackTrace();
223 }
224 return null;
225 }
226
227 @Override
228 protected void onPostExecute(Bitmap bitmap) {
229 super.onPostExecute(bitmap);
230 // 展示图片
231 if (bitmap != null) {
232 // 1.缩放图片
233 // 2.新建ImageView
234 // 3.找到需要的linerlayout添加imageView
235 float width = bitmap.getWidth();
236 float radio = width / mFirstColumn.getWidth();
237 float scaleHeight = bitmap.getHeight() / radio;
238 addImage(bitmap, mFirstColumn.getWidth(), scaleHeight);
239 }
240 mTasks.remove(this);
241 }
242
243 /**
244 * 向ImageView中添加一张图片
245 *
246 * @param bitmap
247 * 待添加的图片
248 * @param width
249 * 图片的宽度
250 * @param scaleHeight
251 * 图片的高度
252 */
253 public void addImage(Bitmap bitmap, float width, float scaleHeight) {
254 // 生成缩放的iv
255 ImageView iv = new ImageView(mContext);
256 android.view.ViewGroup.LayoutParams params = new LayoutParams(
257 (int) width, (int) scaleHeight);
258 iv.setLayoutParams(params);
259 if (bitmap != null) {
260 // 解决默认图片有大有小的问题
261 iv.setScaleType(ScaleType.FIT_XY);
262 iv.setPadding(5, 5, 5, 5);
263
264 iv.setImageBitmap(bitmap);
265 iv.setTag(R.string.iamgurl, mImageUrl);
266 findColumnToAdd(iv, (int) scaleHeight).addView(iv);
267 mImageViewList.add(iv);
268 }
269 }
270
271 }
272
273 /**将图片下载到SD卡缓存起来。
274 * @param imageUrl 图片的URL地址。
275 * @return
276 * @throws IOException
277 */
278 private Bitmap downLoad(String imageUrl) throws IOException {
279 BufferedInputStream bis = null;
280 FileOutputStream fos = null;
281 BufferedOutputStream bos = null;
282 HttpURLConnection conn = null;
283 File imageFile = null;
284 try {
285 URL url = new URL(imageUrl);
286 conn = (HttpURLConnection) url.openConnection();
287 conn.setReadTimeout(10000);
288 conn.setConnectTimeout(5000);
289 conn.setDoInput(true);
290 conn.setDoOutput(true);
291 InputStream is = conn.getInputStream();
292 imageFile = new File(getImagePath(imageUrl));
293 bis = new BufferedInputStream(is);
294 fos = new FileOutputStream(imageFile);
295 bos = new BufferedOutputStream(fos);
296 int len = 0;
297 byte[] buffer = new byte[1024];
298 while ((len = bis.read(buffer)) != -1) {
299 bos.write(buffer, 0, len);
300 bos.flush();
301 }
302 } catch (Exception e) {
303 e.printStackTrace();
304 } finally {
305 if (bis != null) {
306 bis.close();
307 }
308 if (bos != null) {
309 bos.close();
310 }
311 if (conn != null) {
312 conn.disconnect();
313 }
314 }
315 // 如果imageFile不为null，将图片添加到memory中
316 if (imageFile != null) {
317 Bitmap bitmap = BitmapFactory.decodeFile(imageFile.getPath());
318 mImagesThoumb.addBitmapToMemoryCache(imageUrl, bitmap);
319 return bitmap;
320 }
321 return null;
322
323 }
324
325
326 /**
327 * 根据传入的URL，对图片进行加载。如果这张图片已经存在于SD卡中，则直接从SD卡里读取，否则就从网络上下载。
328 *
329 * @param imageUrl
330 * 图片的URL地址
331 * @return 加载到内存的图片。
332 * 判断图片sdcard是否有图片,如果有就用，没有就下载
333 */
334 public Bitmap loadImage(String mImageUrl) throws Exception {
335 File file = new File(getImagePath(mImageUrl));
336 if (!file.exists()) {
337 downLoad(mImageUrl);
338 }
339
340 if (mImageUrl != null) {
341 // 处理本地图片，设置大小防止oom
342 Bitmap bitmap = mImagesThoumb.decodeSimpleBitMapFromResource(
343 file.getPath(), mClolumnWidth);
344 // Bitmap bitmap = BitmapFactory.decodeFile(file.getPath());
345 if (bitmap != null) {
346 mImagesThoumb.addBitmapToMemoryCache(mImageUrl, bitmap);
347 return bitmap;
348 }
349 }
350 return null;
351 }
352
353 /**
354 * 找到此时应该添加图片的一列。原则就是对三列的高度进行判断，当前高度最小的一列就是应该添加的一列。
355 *
356 * @param iv
357 * @param imageHeight
358 * @return 应该添加图片的一列
359 */
360 private LinearLayout findColumnToAdd(ImageView iv, int imageHeight) {
361 if (mFirstColumnHeight <= mSecondColumnHeight) {
362 if (mFirstColumnHeight <= mThirdColumnHeight) {
363 iv.setTag(R.string.border_top, mFirstColumnHeight);
364 mFirstColumnHeight += imageHeight;
365 iv.setTag(R.string.border_bottom, mFirstColumnHeight);
366 return mFirstColumn;
367 }
368 iv.setTag(R.string.border_top, mThirdColumnHeight);
369 mThirdColumnHeight += imageHeight;
370 iv.setTag(R.string.border_bottom, mThirdColumnHeight);
371 return mThirdColumn;
372
373 } else {
374 if (mSecondColumnHeight <= mThirdColumnHeight) {
375 iv.setTag(R.string.border_top, mSecondColumnHeight);
376 mSecondColumnHeight += imageHeight;
377 iv.setTag(R.string.border_bottom, mSecondColumnHeight);
378 return mSecondColumn;
379 }
380 iv.setTag(R.string.border_top, mThirdColumnHeight);
381 mThirdColumnHeight += imageHeight;
382 iv.setTag(R.string.border_bottom, mThirdColumnHeight);
383 return mThirdColumn;
384 }
385 }
386
387 /**获取图片的本地存储路径。
388 * 获得file地址
389 *
390 * @param imageUrl 图片的URL地址。
391 * @return 图片的本地存储路径。
392 */
393 private String getImagePath(String imageUrl) {
394 int lastIndexOf = imageUrl.lastIndexOf("/");
395 String imageName = imageUrl.substring(lastIndexOf + 1);
396 String imageDir = Environment.getExternalStorageDirectory().getPath()
397 + "/pangzaifei/";
398 File file = new File(imageDir);
399 if (!file.exists()) {
400 file.mkdir();
401 }
402 String imagePath = imageDir + imageName;
403 return imagePath;
404 }
405
406 /**判断手机是否有sd卡
407 * 获得图片的名字
408 *
409 * @param imageUrl
410 */
411
412 private boolean hashSdcard() {
413 if (Environment.getExternalStorageState().equals(
414 Environment.MEDIA_MOUNTED)) {
415 return true;
416 }
417 return false;
418 }
419
420 @Override
421 /**
422 * 当手势抬起时，开始每个5毫秒计算位置
423 * 监听用户的触屏事件，如果用户手指离开屏幕则开始进行滚动检测。
424 */
425 public boolean onTouch(View v, MotionEvent event) {
426 if (event.getAction() == MotionEvent.ACTION_UP) {
427 // 发送handler
428 Message msg = mHandler.obtainMessage();
429 msg.obj = this;
430 mHandler.sendMessageDelayed(msg, mDelay);
431 }
432 return false;
433 }
434
435 /**
436 * 在Handler中进行图片可见性检测的判断，以及加载更多图片的操作
437 */
438 private Handler mHandler = new Handler() {
439
440 @Override
441 public void handleMessage(Message msg) {
442 super.handleMessage(msg);
443 // 判断是否已经滑到了最低处，如果滑到了最低处，则加载更多页面，否则继续发送handler扫描
444 PhotoFallScrollView scrollView = (PhotoFallScrollView) msg.obj;
445 int scrollY = scrollView.getScrollY();
446 //如果当前的滚动位置和上次相同，表示已停止滚动
447 if (scrollY == lastScrollY) {
448 // 当滚动的最底部，并且当前没有正在下载的任务时，开始加载下一页的图片
449 if (mScrollViewHeight + scrollY >= mScrollLayout.getHeight()
450 && mTasks.isEmpty()) {
451 scrollView.loadMoreImages();
452 }
453 scrollView.checkVisibile();
454 } else {
455 lastScrollY = scrollY;
456 Message message = new Message();
457 message.obj = scrollView;
458 //5毫秒后在对滚动位置进行判断
459 mHandler.sendMessageDelayed(message, mDelay);
460 }
461 }
462
463 };
464 /**
465 * MyScrollView布局的高度。
466 */
467 private int mScrollViewHeight;
468 /**
469 * MyScrollView下的直接子布局。
470 */
471 private View mScrollLayout;
472
473 /**
474 * 遍历imageview中的每一张图片，对图片的可见性进行检测，如果图片已经离开屏幕可见范围，
475 * 则将图片替换成一张空图
476 * 想不可见的变为空图片
477 */
478 protected void checkVisibile() {
479 if (mImageViewList != null && mImageViewList.size() > 0) {
480 for (int i = 0; i < mImageViewList.size(); i++) {
481 ImageView iv = mImageViewList.get(i);
482 int borderTop = (Integer) iv.getTag(R.string.border_top);
483 int borderBottom = (Integer) iv.getTag(R.string.border_bottom);
484 if (borderBottom > getScrollY()
485 && borderTop < getScrollY() + mScrollViewHeight) {
486 String imageUrl = (String) iv.getTag(R.string.iamgurl);
487 if (imageUrl != null && !"".equals(imageUrl)) {
488 Bitmap bitmap = mImagesThoumb.getMemoryCache(imageUrl);
489 if (bitmap != null) {
490 iv.setImageBitmap(bitmap);
491 } else {
492 downLoadData(imageUrl);
493 }
494 }
495 } else {
496 //离开屏幕加载空图
497 iv.setImageResource(R.drawable.empty_photo);
498 }
499
500 }
501 }
502 }
503 }
时间： 2024-10-10 06:24:06