面对同样的情况，感谢@CommonsWare 的讨论。在此处发布完整的解决方案，以帮助更多人来这里解决相同的问题。欢迎编辑和评论。干杯
When should I recycle a bitmap using LRUCache?
正是当您的位图既不在缓存中也不被任何 ImageView 引用时。
为了维护位图的引用计数，我们必须扩展 BitmapDrawable 类并向它们添加引用属性。
这个 android 示例有确切的答案。
显示位图.zip
我们将在下面了解详细信息和代码。
(don't recycle the bitmaps in the entryRemoved() call).
不完全是。
在 entryRemoved 委托中，检查 Bitmap 是否仍被任何 ImageView 引用。如果不。自己在那里回收。
反之亦然，在接受的答案中提到，当视图即将被重用或被转储时，检查它的位图（如果视图被重用，则为前一个位图）是否在缓存中。如果它在那里，别管它，否则回收它。
这里的关键是我们需要在这两个地方检查我们是否可以回收位图。
我将解释我使用 LruCache 为我保存位图的具体情况。并在 ListView 中显示它们。并在不再使用位图时调用回收。
上面提到的示例的RecyclingBitmapDrawable.java和RecyclingImageView.java是我们这里需要的核心部分。他们处理事情很漂亮。他们的setIsCached和setIsDisplayed方法正在做我们需要的事情。
代码可以在上面提到的示例链接中找到。但也要在答案底部发布文件的完整代码，以防将来链接断开或更改。对覆盖 setImageResource 进行了小修改，以检查先前位图的状态。
--- 这里是你的代码 ---
所以你的 LruCache 管理器应该看起来像这样。
LruCacheManager.java
package com.example.cache;
import android.os.Build;
import android.support.v4.util.LruCache;
public class LruCacheManager {
private LruCache<String, RecyclingBitmapDrawable> mMemoryCache;
private static LruCacheManager instance;
public static LruCacheManager getInstance() {
if(instance == null) {
instance = new LruCacheManager();
instance.init();
}
return instance;
}
private void init() {
// We are declaring a cache of 6Mb for our use.
// You need to calculate this on the basis of your need
mMemoryCache = new LruCache<String, RecyclingBitmapDrawable>(6 * 1024 * 1024) {
@Override
protected int sizeOf(String key, RecyclingBitmapDrawable bitmapDrawable) {
// The cache size will be measured in kilobytes rather than
// number of items.
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR1) {
return bitmapDrawable.getBitmap().getByteCount() ;
} else {
return bitmapDrawable.getBitmap().getRowBytes() * bitmapDrawable.getBitmap().getHeight();
}
}
@Override
protected void entryRemoved(boolean evicted, String key, RecyclingBitmapDrawable oldValue, RecyclingBitmapDrawable newValue) {
super.entryRemoved(evicted, key, oldValue, newValue);
oldValue.setIsCached(false);
}
};
}
public void addBitmapToMemoryCache(String key, RecyclingBitmapDrawable bitmapDrawable) {
if (getBitmapFromMemCache(key) == null) {
// The removed entry is a recycling drawable, so notify it
// that it has been added into the memory cache
bitmapDrawable.setIsCached(true);
mMemoryCache.put(key, bitmapDrawable);
}
}
public RecyclingBitmapDrawable getBitmapFromMemCache(String key) {
return mMemoryCache.get(key);
}
public void clear() {
mMemoryCache.evictAll();
}
}
您的 ListView/GridView 适配器的getView()应该看起来像往常一样正常。就像您使用 setImageDrawable 方法在 ImageView 上设置新图像一样。它在内部检查前一个位图的引用计数，如果不在 lrucache 中，它将在内部调用它的回收。
@Override
public View getView(int position, View convertView, ViewGroup parent) {
RecyclingImageView imageView;
if (convertView == null) { // if it's not recycled, initialize some attributes
imageView = new RecyclingImageView(getActivity());
imageView.setLayoutParams(new GridView.LayoutParams(
GridView.LayoutParams.WRAP_CONTENT,
GridView.LayoutParams.WRAP_CONTENT));
imageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
imageView.setPadding(5, 5, 5, 5);
} else {
imageView = (RecyclingImageView) convertView;
}
MyDataObject dataItem = (MyDataObject) getItem(position);
RecyclingBitmapDrawable image = lruCacheManager.getBitmapFromMemCache(dataItem.getId());
if(image != null) {
// This internally is checking reference count on previous bitmap it used.
imageView.setImageDrawable(image);
} else {
// You have to implement this method as per your code structure.
// But it basically doing is preparing bitmap in the background
// and adding that to LruCache.
// Also it is setting the empty view till bitmap gets loaded.
// once loaded it just need to call notifyDataSetChanged of adapter.
loadImage(dataItem.getId(), R.drawable.empty_view);
}
return imageView;
}
这是你的RecyclingImageView.java
/*
* Copyright (C) 2013 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.cache;
import android.content.Context;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.LayerDrawable;
import android.util.AttributeSet;
import android.widget.ImageView;
/**
* Sub-class of ImageView which automatically notifies the drawable when it is
* being displayed.
*/
public class RecyclingImageView extends ImageView {
public RecyclingImageView(Context context) {
super(context);
}
public RecyclingImageView(Context context, AttributeSet attrs) {
super(context, attrs);
}
/**
* @see android.widget.ImageView#onDetachedFromWindow()
*/
@Override
protected void onDetachedFromWindow() {
// This has been detached from Window, so clear the drawable
setImageDrawable(null);
super.onDetachedFromWindow();
}
/**
* @see android.widget.ImageView#setImageDrawable(android.graphics.drawable.Drawable)
*/
@Override
public void setImageDrawable(Drawable drawable) {
// Keep hold of previous Drawable
final Drawable previousDrawable = getDrawable();
// Call super to set new Drawable
super.setImageDrawable(drawable);
// Notify new Drawable that it is being displayed
notifyDrawable(drawable, true);
// Notify old Drawable so it is no longer being displayed
notifyDrawable(previousDrawable, false);
}
/**
* @see android.widget.ImageView#setImageResource(android.graphics.drawable.Drawable)
*/
@Override
public void setImageResource(int resId) {
// Keep hold of previous Drawable
final Drawable previousDrawable = getDrawable();
// Call super to set new Drawable
super.setImageResource(resId);
// Notify old Drawable so it is no longer being displayed
notifyDrawable(previousDrawable, false);
}
/**
* Notifies the drawable that it's displayed state has changed.
*
* @param drawable
* @param isDisplayed
*/
private static void notifyDrawable(Drawable drawable, final boolean isDisplayed) {
if (drawable instanceof RecyclingBitmapDrawable) {
// The drawable is a CountingBitmapDrawable, so notify it
((RecyclingBitmapDrawable) drawable).setIsDisplayed(isDisplayed);
} else if (drawable instanceof LayerDrawable) {
// The drawable is a LayerDrawable, so recurse on each layer
LayerDrawable layerDrawable = (LayerDrawable) drawable;
for (int i = 0, z = layerDrawable.getNumberOfLayers(); i < z; i++) {
notifyDrawable(layerDrawable.getDrawable(i), isDisplayed);
}
}
}
}
这是你的RecyclingBitmapDrawable.java
/*
* Copyright (C) 2013 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.cache;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.drawable.BitmapDrawable;
import android.util.Log;
/**
* A BitmapDrawable that keeps track of whether it is being displayed or cached.
* When the drawable is no longer being displayed or cached,
* {@link android.graphics.Bitmap#recycle() recycle()} will be called on this drawable's bitmap.
*/
public class RecyclingBitmapDrawable extends BitmapDrawable {
static final String TAG = "CountingBitmapDrawable";
private int mCacheRefCount = 0;
private int mDisplayRefCount = 0;
private boolean mHasBeenDisplayed;
public RecyclingBitmapDrawable(Resources res, Bitmap bitmap) {
super(res, bitmap);
}
/**
* Notify the drawable that the displayed state has changed. Internally a
* count is kept so that the drawable knows when it is no longer being
* displayed.
*
* @param isDisplayed - Whether the drawable is being displayed or not
*/
public void setIsDisplayed(boolean isDisplayed) {
//BEGIN_INCLUDE(set_is_displayed)
synchronized (this) {
if (isDisplayed) {
mDisplayRefCount++;
mHasBeenDisplayed = true;
} else {
mDisplayRefCount--;
}
}
// Check to see if recycle() can be called
checkState();
//END_INCLUDE(set_is_displayed)
}
/**
* Notify the drawable that the cache state has changed. Internally a count
* is kept so that the drawable knows when it is no longer being cached.
*
* @param isCached - Whether the drawable is being cached or not
*/
public void setIsCached(boolean isCached) {
//BEGIN_INCLUDE(set_is_cached)
synchronized (this) {
if (isCached) {
mCacheRefCount++;
} else {
mCacheRefCount--;
}
}
// Check to see if recycle() can be called
checkState();
//END_INCLUDE(set_is_cached)
}
private synchronized void checkState() {
//BEGIN_INCLUDE(check_state)
// If the drawable cache and display ref counts = 0, and this drawable
// has been displayed, then recycle
if (mCacheRefCount <= 0 && mDisplayRefCount <= 0 && mHasBeenDisplayed
&& hasValidBitmap()) {
Log.d(TAG, "No longer being used or cached so recycling. "
+ toString());
getBitmap().recycle();
}
//END_INCLUDE(check_state)
}
private synchronized boolean hasValidBitmap() {
Bitmap bitmap = getBitmap();
return bitmap != null && !bitmap.isRecycled();
}
}