在没有外部 SD 卡的情况下缓存位图 [英] Caching bitmaps without External SD Card
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问题描述
图像不会缓存在内部存储上，也不会在没有外部 SD 卡的设备上崩溃.我已经尝试了我所知道的，但没有任何效果.这是 ImageCache.java
The images will not cache on internal storage and crashes on devices without an External SD Card. I have tried what I know and nothing worked. Here is the 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<String, BitmapDrawable> mMemoryCache;
private ImageCacheParams mCacheParams;
private final Object mDiskCacheLock = new Object();
private boolean mDiskCacheStarting = true;
private HashSet<SoftReference<Bitmap>> 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<Bitmap>>();
}
mMemoryCache = new LruCache<String, BitmapDrawable>(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<Bitmap>(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<Bitmap>> 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 < 0.05 or > .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 < 0.05f || 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 <code>candidate</code> can be used for inBitmap re-use with
* <code>targetOptions</code>
*/
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
And here is the stack trace from Google Developer Console
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.<init>(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
推荐答案
这个:
Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) ||
!isExternalStorageRemovable() ?
getExternalCacheDir(context).getPath() : context.getCacheDir().getPath();
可疑，!isExternalStorageRemovable() 检查覆盖了 MEDIA_MOUNTED 检查.仅仅因为外部存储不可移动，并不意味着它不能被卸载.例如，在旧版本的 android 上，默认行为是将外部存储安装为主机上的 USB 大容量存储.这将卸载它并使您的应用程序无法使用它，无论是否可以物理移除存储介质.
is suspect, the !isExternalStorageRemovable() check overrides the MEDIA_MOUNTED check. Just because external storage is not removable, does not mean it cannot be unmounted. For example, on older versions of android, the default behavior was to mount the external storage as USB mass storage on the host computer. This would unmount it and make it unavailable to your application, regardless of whether the storage media could be physically removed or not.
如果外部存储不可移动，但尚未安装，getExternalCacheDir() 将返回 null.
In the case that external storage was not removable, yet not mounted, getExternalCacheDir() will return null.
这里假设 context 也是非空的.
This is assuming that context is non-null as well.
这篇关于在没有外部 SD 卡的情况下缓存位图的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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