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实现二级缓存加载图片的功能,在使用DiskLruCache时,需先在工程中添加名为libcore.io的包,并将DiskLruCache.Java文件放进去。DiskLruCache直接百度下载即可。
在GridView的适配器中,为ImageView添加图片时,先从内存缓存中加载,内存中无缓存的话则在磁盘缓存中加载,磁盘缓存也没有的话开启线程下载,然后将下载的图片缓存到磁盘,内存中。下载的图片最好先进行压缩,文章最后给出了压缩代码,但本例中并未实现压缩。
/*二级缓存实现图片墙功能,先在内存中加载缓存,内存中无缓存的话到磁盘缓存中加载,仍然没有的话开启线程下载图片,下载后缓存到磁盘中,然后缓存到内存中*/
public class ErJiHuanCun extends ArrayAdapter<String> { /** * 记录所有正在下载或等待下载的任务。 */ private Set<BitmapWorkerTask> taskCollection; /** * 图片缓存技术的核心类,用于缓存所有下载好的图片,在程序内存达到设定值时会将最少最近使用的图片移除掉。 */ private LruCache<String, Bitmap> mMemoryCache; /** * 图片硬盘缓存核心类。 */ private DiskLruCache mDiskLruCache; /** * GridView的实例 */ private GridView mPhotoWall; /** * 记录每个子项的高度。 */ private int mItemHeight = 0; public ErJiHuanCun(Context context, int textViewResourceId, String[] objects, GridView photoWall) { super(context, textViewResourceId, objects); mPhotoWall = photoWall; taskCollection = new HashSet<BitmapWorkerTask>(); // 获取应用程序最大可用内存 int maxMemory = (int) Runtime.getRuntime().maxMemory(); int cacheSize = maxMemory / 8; // 设置图片缓存大小为程序最大可用内存的1/8 mMemoryCache = new LruCache<String, Bitmap>(cacheSize) { @Override protected int sizeOf(String key, Bitmap bitmap) { return bitmap.getByteCount(); } }; try { // 获取图片缓存路径 File cacheDir = getDiskCacheDir(context, "thumb"); if (!cacheDir.exists()) { cacheDir.mkdirs(); } // 创建DiskLruCache实例,初始化缓存数据 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; } // 给ImageView设置一个Tag,保证异步加载图片时不会乱序 imageView.setTag(url); imageView.setImageResource(R.drawable.ic_launcher); loadBitmaps(imageView, url); return view; } /** * 将一张图片存储到LruCache中。 * * @param key * LruCache的键,这里传入图片的URL地址。 * @param bitmap * LruCache的键,这里传入从网络上下载的Bitmap对象。 */ public void addBitmapToMemoryCache(String key, Bitmap bitmap) { if (getBitmapFromMemoryCache(key) == null) { mMemoryCache.put(key, bitmap); } } /** * 从LruCache中获取一张图片,如果不存在就返回null。 * * @param key * LruCache的键,这里传入图片的URL地址。 * @return 对应传入键的Bitmap对象,或者null。 */ public Bitmap getBitmapFromMemoryCache(String key) { return mMemoryCache.get(key); } /** * 加载Bitmap对象。此方法会在LruCache中检查所有屏幕中可见的ImageView的Bitmap对象, * 如果发现任何一个ImageView的Bitmap对象不在缓存中,就会开启异步线程去下载图片。 */ 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(); } } /** * 取消所有正在下载或等待下载的任务。 */ public void cancelAllTasks() { if (taskCollection != null) { for (BitmapWorkerTask task : taskCollection) { task.cancel(false); } } } /** * 根据传入的uniqueName获取硬盘缓存的路径地址。 */ 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); } /** * 获取当前应用程序的版本号。 */ public int getAppVersion(Context context) { try { PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 0); return info.versionCode; } catch (NameNotFoundException e) { e.printStackTrace(); } return 1; } /** * 设置item子项的高度。 */ public void setItemHeight(int height) { if (height == mItemHeight) { return; } mItemHeight = height; notifyDataSetChanged(); } /** * 使用MD5算法对传入的key进行加密并返回。 */ 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; } /** * 将缓存记录同步到journal文件中。 */ public void flushCache() { 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(); } /** * 异步下载图片的任务。 * * */ class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> { /** * 图片的URL地址 */ private String imageUrl; @Override protected Bitmap doInBackground(String... params) { imageUrl = params[0]; FileDescriptor fileDescriptor = null; FileInputStream fileInputStream = null; Snapshot snapShot = null; try { // 生成图片URL对应的key final String key = hashKeyForDisk(imageUrl); // 查找key对应的缓存 snapShot = mDiskLruCache.get(key); if (snapShot == null) { // 如果没有找到对应的缓存,则准备从网络上请求数据,并写入缓存 DiskLruCache.Editor editor = mDiskLruCache.edit(key); if (editor != null) { OutputStream outputStream = editor.newOutputStream(0); if (downloadUrlToStream(imageUrl, outputStream)) { editor.commit(); } else { editor.abort(); } } // 缓存被写入后,再次查找key对应的缓存 snapShot = mDiskLruCache.get(key); } if (snapShot != null) { fileInputStream = (FileInputStream) snapShot.getInputStream(0); fileDescriptor = fileInputStream.getFD(); } // 将缓存数据解析成Bitmap对象 Bitmap bitmap = null; if (fileDescriptor != null) { // bitmap = BitmapFactory.decodeFileDescriptor(fileDescriptor); WindowManager wm= (WindowManager)getContext().getSystemService(Context.WINDOW_SERVICE); int width=wm.getDefaultDisplay().getWidth(); bitmap= ImageResizer.decodeSampleBithmapFromFileDescriptor(fileDescriptor,width/3,width/3); } if (bitmap != null) { // 将Bitmap对象添加到内存缓存当中 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); // 根据Tag找到相应的ImageView控件,将下载好的图片显示出来。 ImageView imageView = (ImageView) mPhotoWall.findViewWithTag(imageUrl); if (imageView != null && bitmap != null) { imageView.setImageBitmap(bitmap); } taskCollection.remove(this); } /** * 建立HTTP请求,并获取Bitmap对象。 * * @param imageUrl * 图片的URL地址 * @return 解析后的Bitmap对象 */ 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; } } }
MainActivity
/** * 照片墙主活动,使用GridView展示照片墙。 * * */ public class MainActivity extends Activity { /** * 用于展示照片墙的GridView */ private GridView mPhotoWall; /** * GridView的适配器 */ private ErJiHuanCun 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 ErJiHuanCun(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(); //将缓存记录同步到journal文件中 mAdapter.flushCache(); } @Override protected void onDestroy() { super.onDestroy(); // // 退出程序时结束所有的下载任务 mAdapter.cancelAllTasks(); } }
/** * 自定义正方形的ImageView * */ public class MyImageView extends ImageView { public MyImageView(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); // TODO Auto-generated constructor stub } public MyImageView(Context context, AttributeSet attrs) { super(context, attrs); // TODO Auto-generated constructor stub } public MyImageView(Context context) { super(context); // TODO Auto-generated constructor stub } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { // TODO Auto-generated method stub //将高度信息改成宽度即可 super.onMeasure(widthMeasureSpec, widthMeasureSpec); } }
主Activity的layout
<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" android:orientation="vertical" android:padding="5dp" > <GridView android:id="@+id/photo_wall" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center" android:horizontalSpacing="5dp" android:verticalSpacing="5dp" android:numColumns="3" android:stretchMode="columnWidth" /> </LinearLayout>
GridView中的Item ImageView
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" > <com.example.imageloader.MyImageView android:layout_width="match_parent" android:layout_height="0dp" android:id="@+id/photo" /> </LinearLayout>
图片压缩实现
public class ImageResizer { private static final String TAG="ImageResizer"; public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId,int reqWidth,int reqHeight){ final BitmapFactory.Options options=new BitmapFactory.Options(); options.inJustDecodeBounds=true; BitmapFactory.decodeResource(res,resId,options); options.inSampleSize=calculateInSampleSize(options,reqWidth,reqHeight); options.inJustDecodeBounds=false; return BitmapFactory.decodeResource(res, resId, options); } public static Bitmap decodeSampleBithmapFromFileDescriptor(FileDescriptor fd, int reqWidth,int reqHeight){ final BitmapFactory.Options options=new BitmapFactory.Options(); options.inJustDecodeBounds=true; BitmapFactory.decodeFileDescriptor(fd, null,options); options.inSampleSize=calculateInSampleSize(options,reqWidth,reqHeight); options.inJustDecodeBounds=false; return BitmapFactory.decodeFileDescriptor(fd, null,options); } public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth,int reqHeight){ if(reqWidth==0||reqHeight==0) return 1; final int width=options.outWidth; final int height=options.outHeight; int inSampleSize=1; if(height>reqHeight||width>reqWidth ){ final int halfHeight=height/2; final int halfWidth=width/2; //尽最大限度的压缩图片,不能让图片的宽高比ImageView的宽高小,否则在将 //图片显示到ImageView时,图片会放大导致图片失真 while(halfHeight/inSampleSize>reqHeight&&halfWidth/inSampleSize>reqWidth){ inSampleSize*=2; } } return inSampleSize; } }
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持亿速云。
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