轉(zhuǎn)載請注明出處：http://blog.csdn.net/guolin_blog/article/details/34093441
在上一篇文章當(dāng)中，我們學(xué)習(xí)了DiskLruCache的概念和基本用法，但僅僅是掌握理論知識顯然是不夠的，那么本篇文章我們就來繼續(xù)進階一下，看一看在實戰(zhàn)當(dāng)中應(yīng)該怎樣合理使用DiskLruCache。還不熟悉DiskLruCache用法的朋友可以先去參考我的上一篇文章?Android DiskLruCache完全解析，硬盤緩存的最佳方案?。
其實，在真正的項目實戰(zhàn)當(dāng)中如果僅僅是使用硬盤緩存的話，程序是有明顯短板的。而如果只使用內(nèi)存緩存的話，程序當(dāng)然也會有很大的缺陷。因此，一個優(yōu)秀的程序必然會將內(nèi)存緩存和硬盤緩存結(jié)合到一起使用，那么本篇文章我們就來看一看，如何才能將LruCache和DiskLruCache完美結(jié)合到一起。
在?Android照片墻應(yīng)用實現(xiàn)，再多的圖片也不怕崩潰?這篇文章當(dāng)中，我編寫了一個照片墻的應(yīng)用程序，但當(dāng)時只是單純使用到了內(nèi)存緩存而已，而今天我們就對這個例子進行擴展，制作一個完整版的照片墻。
那我們開始動手吧，新建一個Android項目，起名叫PhotoWallDemo，這里我使用的是Android 4.0的API。然后新建一個libcore.io包，并將DiskLruCache.Java文件拷貝到這個包下，這樣就把準備工作完成了。
接下來首先需要考慮的仍然是圖片源的問題，簡單起見，我仍然是吧所有圖片都上傳到了我的CSDN相冊當(dāng)中，然后新建一個Images類，將所有相冊中圖片的網(wǎng)址都配置進去，代碼如下所示：
[java]?view plaincopy
public?class?Images?{????????public?final?static?String[]?imageThumbUrls?=?new?String[]?{??????????"https://img-my.csdn.net/uploads/201407/26/1406383299_1976.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383291_6518.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383291_8239.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383290_9329.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383290_1042.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383275_3977.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383265_8550.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383264_3954.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383264_4787.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383264_8243.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383248_3693.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383243_5120.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383242_3127.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383242_9576.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383242_1721.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383219_5806.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383214_7794.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383213_4418.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383213_3557.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383210_8779.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383172_4577.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383166_3407.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383166_2224.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383166_7301.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383165_7197.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383150_8410.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383131_3736.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383130_5094.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383130_7393.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383129_8813.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383100_3554.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383093_7894.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383092_2432.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383092_3071.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383091_3119.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383059_6589.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383059_8814.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383059_2237.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383058_4330.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406383038_3602.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382942_3079.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382942_8125.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382942_4881.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382941_4559.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382941_3845.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382924_8955.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382923_2141.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382923_8437.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382922_6166.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382922_4843.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382905_5804.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382904_3362.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382904_2312.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382904_4960.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382900_2418.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382881_4490.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382881_5935.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382880_3865.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382880_4662.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382879_2553.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382862_5375.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382862_1748.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382861_7618.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382861_8606.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382861_8949.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382841_9821.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382840_6603.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382840_2405.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382840_6354.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382839_5779.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382810_7578.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382810_2436.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382809_3883.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382809_6269.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382808_4179.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382790_8326.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382789_7174.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382789_5170.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382789_4118.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382788_9532.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382767_3184.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382767_4772.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382766_4924.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382766_5762.jpg",??????????"https://img-my.csdn.net/uploads/201407/26/1406382765_7341.jpg"??????};??}?? 設(shè)置好了圖片源之后，我們需要一個GridView來展示照片墻上的每一張圖片。打開或修改activity_main.xml中的代碼，如下所示：
[html]?view plaincopy
<LinearLayout?xmlns:android="http://schemas.android.com/apk/res/android"??????xmlns:tools="http://schemas.android.com/tools"??????android:layout_width="match_parent"??????android:layout_height="match_parent"?>????????<GridView??????????android:id="@+id/photo_wall"??????????android:layout_width="match_parent"??????????android:layout_height="match_parent"??????????android:columnWidth="@dimen/image_thumbnail_size"??????????android:gravity="center"??????????android:horizontalSpacing="@dimen/image_thumbnail_spacing"??????????android:numColumns="auto_fit"??????????android:stretchMode="columnWidth"??????????android:verticalSpacing="@dimen/image_thumbnail_spacing"?>??????</GridView>????</LinearLayout>?? 很簡單，只是在LinearLayout中寫了一個GridView而已。接著我們要定義GridView中每一個子View的布局，新建一個photo_layout.xml布局，加入如下代碼：
[html]?view plaincopy
<RelativeLayout?xmlns:android="http://schemas.android.com/apk/res/android"??????xmlns:tools="http://schemas.android.com/tools"??????android:layout_width="wrap_content"??????android:layout_height="wrap_content"?>????????<ImageView???????????android:id="@+id/photo"??????????android:layout_width="match_parent"??????????android:layout_height="match_parent"??????????android:layout_centerInParent="true"??????????android:scaleType="fitXY"??????????/>????</RelativeLayout>?? 仍然很簡單，photo_layout.xml布局中只有一個ImageView控件，就是用它來顯示圖片的。這樣我們就把所有的布局文件都寫好了。
?
接下來新建PhotoWallAdapter做為GridView的適配器，代碼如下所示：
[java]?view plaincopy
public?class?PhotoWallAdapter?extends?ArrayAdapter<String>?{????????????private?Set<BitmapWorkerTask>?taskCollection;????????????private?LruCache<String,?Bitmap>?mMemoryCache;????????????private?DiskLruCache?mDiskLruCache;????????????private?GridView?mPhotoWall;????????????private?int?mItemHeight?=?0;????????public?PhotoWallAdapter(Context?context,?int?textViewResourceId,?String[]?objects,??????????????GridView?photoWall)?{??????????super(context,?textViewResourceId,?objects);??????????mPhotoWall?=?photoWall;??????????taskCollection?=?new?HashSet<BitmapWorkerTask>();??????????????????int?maxMemory?=?(int)?Runtime.getRuntime().maxMemory();??????????int?cacheSize?=?maxMemory?/?8;??????????????????mMemoryCache?=?new?LruCache<String,?Bitmap>(cacheSize)?{??????????????@Override??????????????protected?int?sizeOf(String?key,?Bitmap?bitmap)?{??????????????????return?bitmap.getByteCount();??????????????}??????????};??????????try?{??????????????????????????File?cacheDir?=?getDiskCacheDir(context,?"thumb");??????????????if?(!cacheDir.exists())?{??????????????????cacheDir.mkdirs();??????????????}??????????????????????????mDiskLruCache?=?DiskLruCache??????????????????????.open(cacheDir,?getAppVersion(context),?1,?10?*?1024?*?1024);??????????}?catch?(IOException?e)?{??????????????e.printStackTrace();??????????}??????}????????@Override??????public?View?getView(int?position,?View?convertView,?ViewGroup?parent)?{??????????final?String?url?=?getItem(position);??????????View?view;??????????if?(convertView?==?null)?{??????????????view?=?LayoutInflater.from(getContext()).inflate(R.layout.photo_layout,?null);??????????}?else?{??????????????view?=?convertView;??????????}??????????final?ImageView?imageView?=?(ImageView)?view.findViewById(R.id.photo);??????????if?(imageView.getLayoutParams().height?!=?mItemHeight)?{??????????????imageView.getLayoutParams().height?=?mItemHeight;??????????}??????????????????imageView.setTag(url);??????????imageView.setImageResource(R.drawable.empty_photo);??????????loadBitmaps(imageView,?url);??????????return?view;??????}????????????public?void?addBitmapToMemoryCache(String?key,?Bitmap?bitmap)?{??????????if?(getBitmapFromMemoryCache(key)?==?null)?{??????????????mMemoryCache.put(key,?bitmap);??????????}??????}????????????public?Bitmap?getBitmapFromMemoryCache(String?key)?{??????????return?mMemoryCache.get(key);??????}????????????public?void?loadBitmaps(ImageView?imageView,?String?imageUrl)?{??????????try?{??????????????Bitmap?bitmap?=?getBitmapFromMemoryCache(imageUrl);??????????????if?(bitmap?==?null)?{??????????????????BitmapWorkerTask?task?=?new?BitmapWorkerTask();??????????????????taskCollection.add(task);??????????????????task.execute(imageUrl);??????????????}?else?{??????????????????if?(imageView?!=?null?&&?bitmap?!=?null)?{??????????????????????imageView.setImageBitmap(bitmap);??????????????????}??????????????}??????????}?catch?(Exception?e)?{??????????????e.printStackTrace();??????????}??????}????????????public?void?cancelAllTasks()?{??????????if?(taskCollection?!=?null)?{??????????????for?(BitmapWorkerTask?task?:?taskCollection)?{??????????????????task.cancel(false);??????????????}??????????}??????}????????????public?File?getDiskCacheDir(Context?context,?String?uniqueName)?{??????????String?cachePath;??????????if?(Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())??????????????????||?!Environment.isExternalStorageRemovable())?{??????????????cachePath?=?context.getExternalCacheDir().getPath();??????????}?else?{??????????????cachePath?=?context.getCacheDir().getPath();??????????}??????????return?new?File(cachePath?+?File.separator?+?uniqueName);??????}????????????public?int?getAppVersion(Context?context)?{??????????try?{??????????????PackageInfo?info?=?context.getPackageManager().getPackageInfo(context.getPackageName(),??????????????????????0);??????????????return?info.versionCode;??????????}?catch?(NameNotFoundException?e)?{??????????????e.printStackTrace();??????????}??????????return?1;??????}????????????public?void?setItemHeight(int?height)?{??????????if?(height?==?mItemHeight)?{??????????????return;??????????}??????????mItemHeight?=?height;??????????notifyDataSetChanged();??????}????????????public?String?hashKeyForDisk(String?key)?{??????????String?cacheKey;??????????try?{??????????????final?MessageDigest?mDigest?=?MessageDigest.getInstance("MD5");??????????????mDigest.update(key.getBytes());??????????????cacheKey?=?bytesToHexString(mDigest.digest());??????????}?catch?(NoSuchAlgorithmException?e)?{??????????????cacheKey?=?String.valueOf(key.hashCode());??????????}??????????return?cacheKey;??????}????????????????public?void?fluchCache()?{??????????if?(mDiskLruCache?!=?null)?{??????????????try?{??????????????????mDiskLruCache.flush();??????????????}?catch?(IOException?e)?{??????????????????e.printStackTrace();??????????????}??????????}??????}????????private?String?bytesToHexString(byte[]?bytes)?{??????????StringBuilder?sb?=?new?StringBuilder();??????????for?(int?i?=?0;?i?<?bytes.length;?i++)?{??????????????String?hex?=?Integer.toHexString(0xFF?&?bytes[i]);??????????????if?(hex.length()?==?1)?{??????????????????sb.append('0');??????????????}??????????????sb.append(hex);??????????}??????????return?sb.toString();??????}????????????class?BitmapWorkerTask?extends?AsyncTask<String,?Void,?Bitmap>?{????????????????????private?String?imageUrl;????????????@Override??????????protected?Bitmap?doInBackground(String...?params)?{??????????????imageUrl?=?params[0];??????????????FileDescriptor?fileDescriptor?=?null;??????????????FileInputStream?fileInputStream?=?null;??????????????Snapshot?snapShot?=?null;??????????????try?{??????????????????????????????????final?String?key?=?hashKeyForDisk(imageUrl);??????????????????????????????????snapShot?=?mDiskLruCache.get(key);??????????????????if?(snapShot?==?null)?{??????????????????????????????????????????DiskLruCache.Editor?editor?=?mDiskLruCache.edit(key);??????????????????????if?(editor?!=?null)?{??????????????????????????OutputStream?outputStream?=?editor.newOutputStream(0);??????????????????????????if?(downloadUrlToStream(imageUrl,?outputStream))?{??????????????????????????????editor.commit();??????????????????????????}?else?{??????????????????????????????editor.abort();??????????????????????????}??????????????????????}??????????????????????????????????????????snapShot?=?mDiskLruCache.get(key);??????????????????}??????????????????if?(snapShot?!=?null)?{??????????????????????fileInputStream?=?(FileInputStream)?snapShot.getInputStream(0);??????????????????????fileDescriptor?=?fileInputStream.getFD();??????????????????}??????????????????????????????????Bitmap?bitmap?=?null;??????????????????if?(fileDescriptor?!=?null)?{??????????????????????bitmap?=?BitmapFactory.decodeFileDescriptor(fileDescriptor);??????????????????}??????????????????if?(bitmap?!=?null)?{??????????????????????????????????????????addBitmapToMemoryCache(params[0],?bitmap);??????????????????}??????????????????return?bitmap;??????????????}?catch?(IOException?e)?{??????????????????e.printStackTrace();??????????????}?finally?{??????????????????if?(fileDescriptor?==?null?&&?fileInputStream?!=?null)?{??????????????????????try?{??????????????????????????fileInputStream.close();??????????????????????}?catch?(IOException?e)?{??????????????????????}??????????????????}??????????????}??????????????return?null;??????????}????????????@Override??????????protected?void?onPostExecute(Bitmap?bitmap)?{??????????????super.onPostExecute(bitmap);??????????????????????????ImageView?imageView?=?(ImageView)?mPhotoWall.findViewWithTag(imageUrl);??????????????if?(imageView?!=?null?&&?bitmap?!=?null)?{??????????????????imageView.setImageBitmap(bitmap);??????????????}??????????????taskCollection.remove(this);??????????}????????????????????private?boolean?downloadUrlToStream(String?urlString,?OutputStream?outputStream)?{??????????????HttpURLConnection?urlConnection?=?null;??????????????BufferedOutputStream?out?=?null;??????????????BufferedInputStream?in?=?null;??????????????try?{??????????????????final?URL?url?=?new?URL(urlString);??????????????????urlConnection?=?(HttpURLConnection)?url.openConnection();??????????????????in?=?new?BufferedInputStream(urlConnection.getInputStream(),?8?*?1024);??????????????????out?=?new?BufferedOutputStream(outputStream,?8?*?1024);??????????????????int?b;??????????????????while?((b?=?in.read())?!=?-1)?{??????????????????????out.write(b);??????????????????}??????????????????return?true;??????????????}?catch?(final?IOException?e)?{??????????????????e.printStackTrace();??????????????}?finally?{??????????????????if?(urlConnection?!=?null)?{??????????????????????urlConnection.disconnect();??????????????????}??????????????????try?{??????????????????????if?(out?!=?null)?{??????????????????????????out.close();??????????????????????}??????????????????????if?(in?!=?null)?{??????????????????????????in.close();??????????????????????}??????????????????}?catch?(final?IOException?e)?{??????????????????????e.printStackTrace();??????????????????}??????????????}??????????????return?false;??????????}????????}????}?? 代碼有點長，我們一點點進行分析。首先在PhotoWallAdapter的構(gòu)造函數(shù)中，我們初始化了LruCache類，并設(shè)置了內(nèi)存緩存容量為程序最大可用內(nèi)存的1/8，緊接著調(diào)用了DiskLruCache的open()方法來創(chuàng)建實例，并設(shè)置了硬盤緩存容量為10M，這樣我們就把LruCache和DiskLruCache的初始化工作完成了。
接著在getView()方法中，我們?yōu)槊總€ImageView設(shè)置了一個唯一的Tag，這個Tag的作用是為了后面能夠準確地找回這個ImageView，不然異步加載圖片會出現(xiàn)亂序的情況。然后在getView()方法的最后調(diào)用了loadBitmaps()方法，加載圖片的具體邏輯也就是在這里執(zhí)行的了。
進入到loadBitmaps()方法中可以看到，實現(xiàn)是調(diào)用了getBitmapFromMemoryCache()方法來從內(nèi)存中獲取緩存，如果獲取到了則直接調(diào)用ImageView的setImageBitmap()方法將圖片顯示到界面上。如果內(nèi)存中沒有獲取到，則開啟一個BitmapWorkerTask任務(wù)（從內(nèi)存獲取不用多線程）來去異步加載圖片。
那么在BitmapWorkerTask的doInBackground()方法中，我們就靈活運用了上篇文章中學(xué)習(xí)的DiskLruCache的各種用法。首先根據(jù)圖片的URL生成對應(yīng)的MD5 key，然后調(diào)用DiskLruCache的get()方法來獲取硬盤緩存，如果沒有獲取到的話則從網(wǎng)絡(luò)上請求圖片并寫入硬盤緩存，接著將Bitmap對象解析出來并添加到內(nèi)存緩存當(dāng)中，最后將這個Bitmap對象顯示到界面上，這樣一個完整的流程就執(zhí)行完了。
那么我們再來分析一下上述流程，每次加載圖片的時候都優(yōu)先去內(nèi)存緩存當(dāng)中讀取，當(dāng)讀取不到的時候則回去硬盤緩存中讀取，而如果硬盤緩存仍然讀取不到的話，就從網(wǎng)絡(luò)上請求原始數(shù)據(jù)。不管是從硬盤緩存還是從網(wǎng)絡(luò)獲取，讀取到了數(shù)據(jù)之后都應(yīng)該添加到內(nèi)存緩存當(dāng)中，這樣的話我們下次再去讀取圖片的時候就能迅速從內(nèi)存當(dāng)中讀取到，而如果該圖片從內(nèi)存中被移除了的話，那就重復(fù)再執(zhí)行一遍上述流程就可以了。
這樣我們就把LruCache和DiskLruCache完美結(jié)合到一起了。接下來還需要編寫MainActivity的代碼，非常簡單，如下所示：
[java]?view plaincopy
public?class?MainActivity?extends?Activity?{????????????private?GridView?mPhotoWall;????????????private?PhotoWallAdapter?mAdapter;????????private?int?mImageThumbSize;??????private?int?mImageThumbSpacing;????????@Override??????protected?void?onCreate(Bundle?savedInstanceState)?{??????????super.onCreate(savedInstanceState);??????????setContentView(R.layout.activity_main);??????????mImageThumbSize?=?getResources().getDimensionPixelSize(??????????????????R.dimen.image_thumbnail_size);??????????mImageThumbSpacing?=?getResources().getDimensionPixelSize(??????????????????R.dimen.image_thumbnail_spacing);??????????mPhotoWall?=?(GridView)?findViewById(R.id.photo_wall);??????????mAdapter?=?new?PhotoWallAdapter(this,?0,?Images.imageThumbUrls,??????????????????mPhotoWall);??????????mPhotoWall.setAdapter(mAdapter);??????????mPhotoWall.getViewTreeObserver().addOnGlobalLayoutListener(??????????????????new?ViewTreeObserver.OnGlobalLayoutListener()?{????????????????????????????????????????????@Override??????????????????????public?void?onGlobalLayout()?{??????????????????????????final?int?numColumns?=?(int)?Math.floor(mPhotoWall??????????????????????????????????.getWidth()??????????????????????????????????/?(mImageThumbSize?+?mImageThumbSpacing));??????????????????????????if?(numColumns?>?0)?{??????????????????????????????int?columnWidth?=?(mPhotoWall.getWidth()?/?numColumns)??????????????????????????????????????-?mImageThumbSpacing;??????????????????????????????mAdapter.setItemHeight(columnWidth);??????????????????????????????mPhotoWall.getViewTreeObserver()??????????????????????????????????????.removeGlobalOnLayoutListener(this);??????????????????????????}??????????????????????}??????????????????});??????}????????????@Override??????protected?void?onPause()?{??????????super.onPause();??????????mAdapter.fluchCache();??????}????????@Override??????protected?void?onDestroy()?{??????????super.onDestroy();??????????????????mAdapter.cancelAllTasks();??????}????}?? 上述代碼中，我們通過getViewTreeObserver()的方式監(jiān)聽View的布局事件，當(dāng)布局完成以后，我們重新修改一下GridView中子View的高度，以保證子View的寬度和高度可以保持一致。
到這里還沒有結(jié)束，最后還需要配置一下AndroidManifest.xml文件，并加入相應(yīng)的權(quán)限，如下所示：
[html]?view plaincopy
<manifest?xmlns:android="http://schemas.android.com/apk/res/android"??????package="com.example.photoswalldemo"??????android:versionCode="1"??????android:versionName="1.0"?>????????<uses-sdk??????????android:minSdkVersion="14"??????????android:targetSdkVersion="17"?/>????????<uses-permission?android:name="android.permission.INTERNET"?/>??????<uses-permission?android:name="android.permission.WRITE_EXTERNAL_STORAGE"?/>????????<application??????????android:allowBackup="true"??????????android:icon="@drawable/ic_launcher"??????????android:label="@string/app_name"??????????android:theme="@style/AppTheme"?>??????????<activity??????????????android:name="com.example.photoswalldemo.MainActivity"??????????????android:label="@string/app_name"?>??????????????<intent-filter>??????????????????<action?android:name="android.intent.action.MAIN"?/>??????????????????<category?android:name="android.intent.category.LAUNCHER"?/>??????????????</intent-filter>??????????</activity>??????</application>????</manifest>?? 好了，全部代碼都在這兒了，讓我們來運行一下吧，效果如下圖所示：
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第一次從網(wǎng)絡(luò)上請求圖片的時候有點慢，但之后加載圖片就會非常快了，滑動起來也很流暢。
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那么我們最后再檢查一下這些圖片是不是已經(jīng)正確緩存在指定地址了，進入?/sdcard/Android/data/<application package>/cache/thumb 這個路徑，如下圖所示：
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可以看到，每張圖片的緩存以及journal文件都在這里了，說明我們的硬盤緩存已經(jīng)成功了。
好了，今天的講解就到這里，有疑問的朋友可以在下面留言。
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源碼下載，請點擊這里
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