在没有外部SD卡的情况下缓存位图
没有外部SD卡，图像不会在内部存储器上缓存并在设备上崩溃。 我尝试过我所知道的，没有任何效果。 这是ImageCache.java
package com.minecraftpix.android.bitmapfun.util; import com.minecraftpix.BuildConfig; import android.annotation.TargetApi; import android.content.Context; import android.graphics.Bitmap; import android.graphics.Bitmap.CompressFormat; import android.graphics.BitmapFactory; import android.graphics.drawable.BitmapDrawable; import android.os.Bundle; import android.os.Environment; import android.os.StatFs; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.util.LruCache; import android.util.Log; import java.io.File; import java.io.FileDescriptor; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.lang.ref.SoftReference; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import java.util.HashSet; import java.util.Iterator; public class ImageCache { private static final String TAG = "ImageCache"; // Default memory cache size in kilobytes private static final int DEFAULT_MEM_CACHE_SIZE = 1024 * 5; // 5MB // Default disk cache size in bytes private static final int DEFAULT_DISK_CACHE_SIZE = 1024 * 1024 * 10; // 10MB // Compression settings when writing images to disk cache private static final CompressFormat DEFAULT_COMPRESS_FORMAT = CompressFormat.JPEG; private static final int DEFAULT_COMPRESS_QUALITY = 70; private static final int DISK_CACHE_INDEX = 0; // Constants to easily toggle various caches private static final boolean DEFAULT_MEM_CACHE_ENABLED = true; private static final boolean DEFAULT_DISK_CACHE_ENABLED = true; private static final boolean DEFAULT_INIT_DISK_CACHE_ON_CREATE = false; private DiskLruCache mDiskLruCache; private LruCache mMemoryCache; private ImageCacheParams mCacheParams; private final Object mDiskCacheLock = new Object(); private boolean mDiskCacheStarting = true; private HashSet<SoftReference> mReusableBitmaps; /** * Create a new ImageCache object using the specified parameters. This should not be * called directly by other classes, instead use * {@link ImageCache#getInstance(FragmentManager, ImageCacheParams)} to fetch an ImageCache * instance. * * @param cacheParams The cache parameters to use to initialize the cache */ private ImageCache(ImageCacheParams cacheParams) { init(cacheParams); } /** * Return an {@link ImageCache} instance. A {@link RetainFragment} is used to retain the * ImageCache object across configuration changes such as a change in device orientation. * * @param fragmentManager The fragment manager to use when dealing with the retained fragment. * @param cacheParams The cache parameters to use if the ImageCache needs instantiation. * @return An existing retained ImageCache object or a new one if one did not exist */ public static ImageCache getInstance( FragmentManager fragmentManager, ImageCacheParams cacheParams) { // Search for, or create an instance of the non-UI RetainFragment final RetainFragment mRetainFragment = findOrCreateRetainFragment(fragmentManager); // See if we already have an ImageCache stored in RetainFragment ImageCache imageCache = (ImageCache) mRetainFragment.getObject(); // No existing ImageCache, create one and store it in RetainFragment if (imageCache == null) { imageCache = new ImageCache(cacheParams); mRetainFragment.setObject(imageCache); } return imageCache; } /** * Initialize the cache, providing all parameters. * * @param cacheParams The cache parameters to initialize the cache */ private void init(ImageCacheParams cacheParams) { mCacheParams = cacheParams; // Set up memory cache if (mCacheParams.memoryCacheEnabled) { if (BuildConfig.DEBUG) { Log.d(TAG, "Memory cache created (size = " + mCacheParams.memCacheSize + ")"); } // If we're running on Honeycomb or newer, then if (Utils.hasHoneycomb()) { mReusableBitmaps = new HashSet<SoftReference>(); } mMemoryCache = new LruCache(mCacheParams.memCacheSize) { /** * Notify the removed entry that is no longer being cached */ @Override protected void entryRemoved(boolean evicted, String key, BitmapDrawable oldValue, BitmapDrawable newValue) { if (RecyclingBitmapDrawable.class.isInstance(oldValue)) { // The removed entry is a recycling drawable, so notify it // that it has been removed from the memory cache ((RecyclingBitmapDrawable) oldValue).setIsCached(false); } else { // The removed entry is a standard BitmapDrawable if (Utils.hasHoneycomb()) { // We're running on Honeycomb or later, so add the bitmap // to a SoftRefrence set for possible use with inBitmap later mReusableBitmaps.add(new SoftReference(oldValue.getBitmap())); } } } /** * Measure item size in kilobytes rather than units which is more practical * for a bitmap cache */ @Override protected int sizeOf(String key, BitmapDrawable value) { final int bitmapSize = getBitmapSize(value) / 1024; return bitmapSize == 0 ? 1 : bitmapSize; } }; } // By default the disk cache is not initialized here as it should be initialized // on a separate thread due to disk access. if (cacheParams.initDiskCacheOnCreate) { // Set up disk cache initDiskCache(); } } /** * Initializes the disk cache. Note that this includes disk access so this should not be * executed on the main/UI thread. By default an ImageCache does not initialize the disk * cache when it is created, instead you should call initDiskCache() to initialize it on a * background thread. */ public void initDiskCache() { // Set up disk cache synchronized (mDiskCacheLock) { if (mDiskLruCache == null || mDiskLruCache.isClosed()) { File diskCacheDir = mCacheParams.diskCacheDir; if (mCacheParams.diskCacheEnabled && diskCacheDir != null) { if (!diskCacheDir.exists()) { diskCacheDir.mkdirs(); } if (getUsableSpace(diskCacheDir) > mCacheParams.diskCacheSize) { try { mDiskLruCache = DiskLruCache.open( diskCacheDir, 1, 1, mCacheParams.diskCacheSize); if (BuildConfig.DEBUG) { Log.d(TAG, "Disk cache initialized"); } } catch (final IOException e) { mCacheParams.diskCacheDir = null; Log.e(TAG, "initDiskCache - " + e); } } } } mDiskCacheStarting = false; mDiskCacheLock.notifyAll(); } } /** * Adds a bitmap to both memory and disk cache. * @param data Unique identifier for the bitmap to store * @param value The bitmap drawable to store */ public void addBitmapToCache(String data, BitmapDrawable value) { if (data == null || value == null) { return; } // Add to memory cache if (mMemoryCache != null) { if (RecyclingBitmapDrawable.class.isInstance(value)) { // The removed entry is a recycling drawable, so notify it // that it has been added into the memory cache ((RecyclingBitmapDrawable) value).setIsCached(true); } mMemoryCache.put(data, value); } synchronized (mDiskCacheLock) { // Add to disk cache if (mDiskLruCache != null) { final String key = hashKeyForDisk(data); OutputStream out = null; try { DiskLruCache.Snapshot snapshot = mDiskLruCache.get(key); if (snapshot == null) { final DiskLruCache.Editor editor = mDiskLruCache.edit(key); if (editor != null) { out = editor.newOutputStream(DISK_CACHE_INDEX); value.getBitmap().compress( mCacheParams.compressFormat, mCacheParams.compressQuality, out); editor.commit(); out.close(); } } else { snapshot.getInputStream(DISK_CACHE_INDEX).close(); } } catch (final IOException e) { Log.e(TAG, "addBitmapToCache - " + e); } catch (Exception e) { Log.e(TAG, "addBitmapToCache - " + e); } finally { try { if (out != null) { out.close(); } } catch (IOException e) {} } } } } /** * Get from memory cache. * * @param data Unique identifier for which item to get * @return The bitmap drawable if found in cache, null otherwise */ public BitmapDrawable getBitmapFromMemCache(String data) { BitmapDrawable memValue = null; if (mMemoryCache != null) { memValue = mMemoryCache.get(data); } if (BuildConfig.DEBUG && memValue != null) { Log.d(TAG, "Memory cache hit"); } return memValue; } /** * Get from disk cache. * * @param data Unique identifier for which item to get * @return The bitmap if found in cache, null otherwise */ public Bitmap getBitmapFromDiskCache(String data) { final String key = hashKeyForDisk(data); Bitmap bitmap = null; synchronized (mDiskCacheLock) { while (mDiskCacheStarting) { try { mDiskCacheLock.wait(); } catch (InterruptedException e) {} } if (mDiskLruCache != null) { InputStream inputStream = null; try { final DiskLruCache.Snapshot snapshot = mDiskLruCache.get(key); if (snapshot != null) { if (BuildConfig.DEBUG) { Log.d(TAG, "Disk cache hit"); } inputStream = snapshot.getInputStream(DISK_CACHE_INDEX); if (inputStream != null) { FileDescriptor fd = ((FileInputStream) inputStream).getFD(); // Decode bitmap, but we don't want to sample so give // MAX_VALUE as the target dimensions bitmap = ImageResizer.decodeSampledBitmapFromDescriptor( fd, Integer.MAX_VALUE, Integer.MAX_VALUE, this); } } } catch (final IOException e) { Log.e(TAG, "getBitmapFromDiskCache - " + e); } finally { try { if (inputStream != null) { inputStream.close(); } } catch (IOException e) {} } } return bitmap; } } /** * @param options - BitmapFactory.Options with out* options populated * @return Bitmap that case be used for inBitmap */ protected Bitmap getBitmapFromReusableSet(BitmapFactory.Options options) { Bitmap bitmap = null; if (mReusableBitmaps != null && !mReusableBitmaps.isEmpty()) { final Iterator<SoftReference> iterator = mReusableBitmaps.iterator(); Bitmap item; while (iterator.hasNext()) { item = iterator.next().get(); if (null != item && item.isMutable()) { // Check to see it the item can be used for inBitmap if (canUseForInBitmap(item, options)) { bitmap = item; // Remove from reusable set so it can't be used again iterator.remove(); break; } } else { // Remove from the set if the reference has been cleared. iterator.remove(); } } } return bitmap; } /** * Clears both the memory and disk cache associated with this ImageCache object. Note that * this includes disk access so this should not be executed on the main/UI thread. */ public void clearCache() { if (mMemoryCache != null) { mMemoryCache.evictAll(); if (BuildConfig.DEBUG) { Log.d(TAG, "Memory cache cleared"); } } synchronized (mDiskCacheLock) { mDiskCacheStarting = true; if (mDiskLruCache != null && !mDiskLruCache.isClosed()) { try { mDiskLruCache.delete(); if (BuildConfig.DEBUG) { Log.d(TAG, "Disk cache cleared"); } } catch (IOException e) { Log.e(TAG, "clearCache - " + e); } mDiskLruCache = null; initDiskCache(); } } } /** * Flushes the disk cache associated with this ImageCache object. Note that this includes * disk access so this should not be executed on the main/UI thread. */ public void flush() { synchronized (mDiskCacheLock) { if (mDiskLruCache != null) { try { mDiskLruCache.flush(); if (BuildConfig.DEBUG) { Log.d(TAG, "Disk cache flushed"); } } catch (IOException e) { Log.e(TAG, "flush - " + e); } } } } /** * Closes the disk cache associated with this ImageCache object. Note that this includes * disk access so this should not be executed on the main/UI thread. */ public void close() { synchronized (mDiskCacheLock) { if (mDiskLruCache != null) { try { if (!mDiskLruCache.isClosed()) { mDiskLruCache.close(); mDiskLruCache = null; if (BuildConfig.DEBUG) { Log.d(TAG, "Disk cache closed"); } } } catch (IOException e) { Log.e(TAG, "close - " + e); } } } } /** * A holder class that contains cache parameters. */ public static class ImageCacheParams { public int memCacheSize = DEFAULT_MEM_CACHE_SIZE; public int diskCacheSize = DEFAULT_DISK_CACHE_SIZE; public File diskCacheDir; public CompressFormat compressFormat = DEFAULT_COMPRESS_FORMAT; public int compressQuality = DEFAULT_COMPRESS_QUALITY; public boolean memoryCacheEnabled = DEFAULT_MEM_CACHE_ENABLED; public boolean diskCacheEnabled = DEFAULT_DISK_CACHE_ENABLED; public boolean initDiskCacheOnCreate = DEFAULT_INIT_DISK_CACHE_ON_CREATE; /** * Create a set of image cache parameters that can be provided to * {@link ImageCache#getInstance(FragmentManager, ImageCacheParams)} or * {@link ImageWorker#addImageCache(FragmentManager, ImageCacheParams)}. * @param context A context to use. * @param diskCacheDirectoryName A unique subdirectory name that will be appended to the * application cache directory. Usually "cache" or "images" * is sufficient. */ public ImageCacheParams(Context context, String diskCacheDirectoryName) { diskCacheDir = getDiskCacheDir(context, diskCacheDirectoryName); } /** * Sets the memory cache size based on a percentage of the max available VM memory. * Eg. setting percent to 0.2 would set the memory cache to one fifth of the available * memory. Throws {@link IllegalArgumentException} if percent is .8. * memCacheSize is stored in kilobytes instead of bytes as this will eventually be passed * to construct a LruCache which takes an int in its constructor. * * This value should be chosen carefully based on a number of factors * Refer to the corresponding Android Training class for more discussion: * http://developer.android.com/training/displaying-bitmaps/ * * @param percent Percent of available app memory to use to size memory cache */ public void setMemCacheSizePercent(float percent) { if (percent 0.8f) { throw new IllegalArgumentException("setMemCacheSizePercent - percent must be " + "between 0.05 and 0.8 (inclusive)"); } memCacheSize = Math.round(percent * Runtime.getRuntime().maxMemory() / 1024); } } /** * @param candidate - Bitmap to check * @param targetOptions - Options that have the out* value populated * @return true if candidate can be used for inBitmap re-use with * targetOptions */ private static boolean canUseForInBitmap( Bitmap candidate, BitmapFactory.Options targetOptions) { int width = targetOptions.outWidth / targetOptions.inSampleSize; int height = targetOptions.outHeight / targetOptions.inSampleSize; return candidate.getWidth() == width && candidate.getHeight() == height; } /** * Get a usable cache directory (external if available, internal otherwise). * * @param context The context to use * @param uniqueName A unique directory name to append to the cache dir * @return The cache dir */ public static File getDiskCacheDir(Context context, String uniqueName) { // Check if media is mounted or storage is built-in, if so, try and use external cache dir // otherwise use internal cache dir final String cachePath = Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) || !isExternalStorageRemovable() ? getExternalCacheDir(context).getPath() : context.getCacheDir().getPath(); return new File(cachePath + File.separator + uniqueName); } /** * A hashing method that changes a string (like a URL) into a hash suitable for using as a * disk filename. */ public static 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; } private static String bytesToHexString(byte[] bytes) { // http://stackoverflow.com/questions/332079 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(); } /** * Get the size in bytes of a bitmap in a BitmapDrawable. * @param value * @return size in bytes */ @TargetApi(12) public static int getBitmapSize(BitmapDrawable value) { Bitmap bitmap = value.getBitmap(); if (Utils.hasHoneycombMR1()) { return bitmap.getByteCount(); } // Pre HC-MR1 return bitmap.getRowBytes() * bitmap.getHeight(); } /** * Check if external storage is built-in or removable. * * @return True if external storage is removable (like an SD card), false * otherwise. */ @TargetApi(9) public static boolean isExternalStorageRemovable() { if (Utils.hasGingerbread()) { return Environment.isExternalStorageRemovable(); } return true; } /** * Get the external app cache directory. * * @param context The context to use * @return The external cache dir */ @TargetApi(8) public static File getExternalCacheDir(Context context) { if (Utils.hasFroyo()) { return context.getExternalCacheDir(); } // Before Froyo we need to construct the external cache dir ourselves final String cacheDir = "/Android/data/" + context.getPackageName() + "/cache/"; return new File(Environment.getExternalStorageDirectory().getPath() + cacheDir); } /** * Check how much usable space is available at a given path. * * @param path The path to check * @return The space available in bytes */ @TargetApi(9) public static long getUsableSpace(File path) { if (Utils.hasGingerbread()) { return path.getUsableSpace(); } final StatFs stats = new StatFs(path.getPath()); return (long) stats.getBlockSize() * (long) stats.getAvailableBlocks(); } /** * Locate an existing instance of this Fragment or if not found, create and * add it using FragmentManager. * * @param fm The FragmentManager manager to use. * @return The existing instance of the Fragment or the new instance if just * created. */ private static RetainFragment findOrCreateRetainFragment(FragmentManager fm) { // Check to see if we have retained the worker fragment. RetainFragment mRetainFragment = (RetainFragment) fm.findFragmentByTag(TAG); // If not retained (or first time running), we need to create and add it. if (mRetainFragment == null) { mRetainFragment = new RetainFragment(); fm.beginTransaction().add(mRetainFragment, TAG).commitAllowingStateLoss(); } return mRetainFragment; } /** * A simple non-UI Fragment that stores a single Object and is retained over configuration * changes. It will be used to retain the ImageCache object. */ public static class RetainFragment extends Fragment { private Object mObject; /** * Empty constructor as per the Fragment documentation */ public RetainFragment() {} @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Make sure this Fragment is retained over a configuration change setRetainInstance(true); } /** * Store a single object in this Fragment. * * @param object The object to store */ public void setObject(Object object) { mObject = object; } /** * Get the stored object. * * @return The stored object */ public Object getObject() { return mObject; } } } 这是来自Google Developer Console的堆栈跟踪
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.minecraftpix/com.minecraftpix.pics.ImageGridActivity}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) at android.app.ActivityThread.access$2300(ActivityThread.java:125) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:123) at android.app.ActivityThread.main(ActivityThread.java:4627) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:521) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at com.minecraftpix.android.bitmapfun.util.ImageCache.getDiskCacheDir(ImageCache.java:514) at com.minecraftpix.android.bitmapfun.util.ImageCache$ImageCacheParams.(ImageCache.java:463) at com.minecraftpix.pics.ImageGridFragment.onCreate(ImageGridFragment.java:80) at android.support.v4.app.Fragment.performCreate(Fragment.java:1437) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:877) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088) at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682) at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1444) at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:551) at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1131) at android.app.Activity.performStart(Activity.java:3781) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2636) ... 11 more
这个：
Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) || !isExternalStorageRemovable() ? getExternalCacheDir(context).getPath() : context.getCacheDir().getPath();
可疑， !isExternalStorageRemovable()检查会覆盖MEDIA_MOUNTED检查。 仅仅因为外部存储不可移动，并不意味着它无法卸载。 例如，在较旧版本的android上，默认行为是将外部存储装载为主机上的USB大容量存储。 无论是否可以物理删除存储介质，这都会将其卸载并使其对您的应用程序不可用。
如果外部存储不可移动但尚未安装，则getExternalCacheDir()将返回null。
这假设context也是非空的。
试试这个..
if(android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED)) { //some stuff }