1.recycle
使用recycle方法可以让系统清理C层所占用的Native内存,这时再调用bitmap的相关方法会引起异常。
public void recycle() {
if (!mRecycled && mNativePtr != 0) {
if (nativeRecycle(mNativePtr)) {
// return value indicates whether native pixel object was actually recycled.
// false indicates that it is still in use at the native level and these
// objects should not be collected now. They will be collected later when the
// Bitmap itself is collected.
mBuffer = null;
mNinePatchChunk = null;
}
mRecycled = true;
}
}
2.LRU
LruCache类内部主要是用LinkedHashMap来实现的,提供了put()和get()方法来进行缓存的添加和获取操作;当缓存满了的时候,会用trimToSize()方法将较早的对象移除。
//用于存放缓存对象
public final V put(K key, V value) {
if (key == null || value == null) {
throw new NullPointerException("key == null || value == null");
}
V previous;
synchronized (this) {
putCount++;
size += safeSizeOf(key, value);
previous = map.put(key, value);
if (previous != null) {
size -= safeSizeOf(key, previous);
}
}
if (previous != null) {
entryRemoved(false, key, previous, value);
}
trimToSize(maxSize);
return previous;
}
//用于移除缓存对象
public final V remove(K key) {
if (key == null) {
throw new NullPointerException("key == null");
}
V previous;
synchronized (this) {
previous = map.remove(key);
if (previous != null) {
size -= safeSizeOf(key, previous);
}
}
if (previous != null) {
entryRemoved(false, key, previous, null);
}
return previous;
}
//用于将较早的缓存对象移除
public void trimToSize(int maxSize) {
while (true) {
K key;
V value;
synchronized (this) {
if (size < 0 || (map.isEmpty() && size != 0)) {
throw new IllegalStateException(getClass().getName()
+ ".sizeOf() is reporting inconsistent results!");
}
if (size <= maxSize || map.isEmpty()) {
break;
}
Map.Entry<K, V> toEvict = map.entrySet().iterator().next();
key = toEvict.getKey();
value = toEvict.getValue();
map.remove(key);
size -= safeSizeOf(key, value);
evictionCount++;
}
entryRemoved(true, key, value, null);
}
}
3.计算inSampleSize
public class BitmapUtils {
public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
if (width > height) {
inSampleSize = Math.round((float) height / (float) reqHeight);
} else {
inSampleSize = Math.round((float) width / (float) reqWidth);
}
}
return inSampleSize;
}
}
4.缩略图
public static Bitmap thumbnail(String path, int maxWidth, int maxHeight, boolean autoRotate) {
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
Bitmap bitmap = BitmapFactory.decodeFile(path, options);
options.inJustDecodeBounds = false;
//计算缩放比
int sampleSize = calculateInSampleSize(options, maxWidth, maxHeight);
options.inSampleSize = sampleSize;
options.inPreferredConfig = Bitmap.Config.RGB_565;
options.inPurgeable = true;
options.inInputShareable = true;
if (bitmap != null && !bitmap.isRecycled()) {
bitmap.recycle();
}
bitmap = BitmapFactory.decodeFile(path, options);
return bitmap;
}
5.三级缓存
①网络缓存
②本地缓存
③内存缓存
第一次打开图片先从网络获取,并保存到本地和内存各一份;再次打开图片就从内存或者本地获取,无需再次联网。