这会有点长，但是如果你能忍受我的话我会很感激，我相信这对其他人也很有用。
我在我的Android应用中使用谷歌地图放置不同的标记。每个标记属于由位图表示的类别。我一直在使用Displaying Bitmaps Efficiently中的 BitmapFun 示例来缓存我的应用中的位图，并尝试使用我的Google地图标记实现相同的解决方案。
我的代码已添加到示例的ImageWorker.java中，如下所示（BitmapWorkerTask已存在且已更新以处理标记）：
private static Map<Marker, BitmapWorkerTask> markerToTaskMap = new HashMap<Marker, BitmapWorkerTask>();
public void loadImage(Object data, Marker marker) {
if (data == null) {
return;
}
BitmapDrawable value = null;
if (mImageCache != null) {
value = mImageCache.getBitmapFromMemCache(String.valueOf(data));
}
if (value != null) {
// Bitmap found in memory cache
marker.setIcon(BitmapDescriptorFactory.fromBitmap(value.getBitmap()));
} else if (cancelPotentialWork(data, marker)) {
final BitmapWorkerTask task = new BitmapWorkerTask(marker);
markerToTaskMap.put(marker, task);
task.executeOnExecutor(AsyncTask.DUAL_THREAD_EXECUTOR, data);
}
}
private class BitmapWorkerTask extends AsyncTask<Object, Void, BitmapDrawable> {
private Object data;
private WeakReference<ImageView> imageViewReference = null;
private WeakReference<Marker> markerReference = null;
public BitmapWorkerTask(ImageView imageView) {
imageViewReference = new WeakReference<ImageView>(imageView);
}
public BitmapWorkerTask(Marker marker) {
markerReference = new WeakReference<Marker>(marker);
}
/**
* Background processing.
*/
@Override
protected BitmapDrawable doInBackground(Object... params) {
if (BuildConfig.DEBUG) {
Log.d(TAG, "doInBackground - starting work");
}
data = params[0];
final String dataString = String.valueOf(data);
Bitmap bitmap = null;
BitmapDrawable drawable = null;
// Wait here if work is paused and the task is not cancelled
synchronized (mPauseWorkLock) {
while (mPauseWork && !isCancelled()) {
try {
mPauseWorkLock.wait();
} catch (InterruptedException e) {}
}
}
// If the image cache is available and this task has not been cancelled by another
// thread and the ImageView that was originally bound to this task is still bound back
// to this task and our "exit early" flag is not set then try and fetch the bitmap from
// the cache
if (mImageCache != null && !isCancelled() && (getAttachedImageView() != null || getAttachedMarker() != null)
&& !mExitTasksEarly) {
bitmap = mImageCache.getBitmapFromDiskCache(dataString);
}
// If the bitmap was not found in the cache and this task has not been cancelled by
// another thread and the ImageView that was originally bound to this task is still
// bound back to this task and our "exit early" flag is not set, then call the main
// process method (as implemented by a subclass)
if (bitmap == null && !isCancelled() && (getAttachedImageView() != null || getAttachedMarker() != null)
&& !mExitTasksEarly) {
bitmap = processBitmap(params[0]);
}
// If the bitmap was processed and the image cache is available, then add the processed
// bitmap to the cache for future use. Note we don't check if the task was cancelled
// here, if it was, and the thread is still running, we may as well add the processed
// bitmap to our cache as it might be used again in the future
if (bitmap != null) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
// Running on Honeycomb or newer, so wrap in a standard BitmapDrawable
drawable = new BitmapDrawable(mResources, bitmap);
} else {
// Running on Gingerbread or older, so wrap in a RecyclingBitmapDrawable
// which will recycle automagically
drawable = new RecyclingBitmapDrawable(mResources, bitmap);
}
if (mImageCache != null) {
mImageCache.addBitmapToCache(dataString, drawable);
}
}
if (BuildConfig.DEBUG) {
Log.d(TAG, "doInBackground - finished work");
}
return drawable;
}
/**
* Once the image is processed, associates it to the imageView
*/
@Override
protected void onPostExecute(BitmapDrawable value) {
// if cancel was called on this task or the "exit early" flag is set then we're done
if (isCancelled() || mExitTasksEarly) {
value = null;
}
if (imageViewReference != null) {
final ImageView imageView = getAttachedImageView();
if (value != null && imageView != null) {
if (BuildConfig.DEBUG) {
Log.d(TAG, "onPostExecute - setting bitmap");
}
setImageDrawable(imageView, value);
}
} else if (markerReference != null) {
final Marker marker = getAttachedMarker();
if (value != null && marker != null) {
if (BuildConfig.DEBUG) {
Log.d(TAG, "onPostExecute - setting marker bitmap");
}
markerToTaskMap.remove(marker);
marker.setIcon(BitmapDescriptorFactory.fromBitmap(value.getBitmap()));
}
}
}
@Override
protected void onCancelled(BitmapDrawable value) {
super.onCancelled(value);
synchronized (mPauseWorkLock) {
mPauseWorkLock.notifyAll();
}
}
/**
* Returns the ImageView associated with this task as long as the ImageView's task still
* points to this task as well. Returns null otherwise.
*/
private ImageView getAttachedImageView() {
if (imageViewReference == null) {
return null;
}
final ImageView imageView = imageViewReference.get();
final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView);
if (this == bitmapWorkerTask) {
return imageView;
}
return null;
}
private Marker getAttachedMarker() {
if (markerReference == null) {
return null;
}
final Marker marker = markerReference.get();
final BitmapWorkerTask bitmapWorkerTask = markerToTaskMap.get(marker); //getBitmapWorkerTask(marker);
if (this == bitmapWorkerTask) {
return marker;
}
return null;
}
}
public static boolean cancelPotentialWork(Object data, Marker marker) {
final BitmapWorkerTask bitmapWorkerTask = markerToTaskMap.get(marker);
if (bitmapWorkerTask != null) {
final Object bitmapData = bitmapWorkerTask.data;
if (bitmapData == null || !bitmapData.equals(data)) {
bitmapWorkerTask.cancel(true);
if (BuildConfig.DEBUG) {
Log.d(TAG, "cancelPotentialWork - cancelled work for " + data);
}
} else {
// The same work is already in progress.
return false;
}
}
return true;
}
如果您熟悉BitmapFun示例，您可以看到一切都与使用带有ImageView的位图几乎相同，只是使用AsyncDrawable将位图连接到其加载的AsyncTask。由于我无法扩展Marker类（它是最终的）并且没有getIcon（）方法，所以我必须维护一个hashmap（markerToTaskMap）来完成这项工作。
这个解决方案似乎一般都有效，除了一些毛刺，我得到一个错误的位图作为标记。我不知道为什么。 OOB示例代码不会发生这种情况。
感谢有人在这里帮助我。感谢。
答案 0 :(得分：3)
我可以通过要求不要这样做来帮助你。
如果你想优化，更好地了解你的敌人。每次调用Google Maps Android API v2都会转到其他进程。其中大部分需要在主线程上完成。
因为对API的每次调用都是同步到达其他进程，所以它将阻止用户界面。例如。在体面的手机上添加2000个标记需要1秒钟（测试过）。另一方面，加载20个小位图来表示onCreate中的类别将花费不到100毫秒（未经测试的声明）。因此，您的代码甚至会降低速度，因为您至少有2次调用才能添加Marker：addMarker和setIcon。
只需使用Bitmap将所有BitmapDescriptorFactory.fromResource加载到Map<Category, BitmapDescriptor>一次，然后在创建Marker时使用它们。
总结一下：除非出现问题，否则不要进行优化。