glide缩略图存储 android,Glide 显示视频缩略图及遇到的坑
Glide 顯示視頻縮略圖及遇到的坑
實(shí)現(xiàn)原理
Glide支持視頻格式的文件，但是在3.x里會(huì)有些欠缺。其底層是通過(guò) MediaMetadataRetriever實(shí)現(xiàn)的。
MediaMetadataRetriever擁有獲取視頻的第幾幀的能力,Glide獲取視頻里的第n幀的代碼如下:
VideoBitmapDecoder.java
@Override
public Bitmap decode(ParcelFileDescriptor resource, BitmapPool bitmapPool, int outWidth, int outHeight,
DecodeFormat decodeFormat)
throws IOException {
MediaMetadataRetriever mediaMetadataRetriever = factory.build();
mediaMetadataRetriever.setDataSource(resource.getFileDescriptor());
Bitmap result;
if (frame >= 0) {
result = mediaMetadataRetriever.getFrameAtTime(frame);
} else {
result = mediaMetadataRetriever.getFrameAtTime();
}
mediaMetadataRetriever.release();
resource.close();
return result;
}
提取核心代碼
mediaMetadataRetriever獲取Bitmap的代碼：
val file = FileInputStream(File(path))
val s = MediaMetadataRetriever()
s.setDataSource(file.fd)
file.close()
val bitmap = s.getFrameAtTime(-1)
imageView.setImageBitmap(bitmap)
s.release()
Glide3.x的一個(gè)bug
但3.x的Glide緩存策略不能是Source我們來(lái)分析各種緩存策略Glide的內(nèi)部的邏輯
Result緩存策略
EngineRunnable.java
private Resource> decode() throws Exception {
if (isDecodingFromCache()) {
return decodeFromCache();
} else {
return decodeFromSource();
}
}
EngineRunnable分走兩次，第一次走isDecodingFromCache
private Resource> decodeFromCache() throws Exception {
Resource> result = null;
//...ignore code
//先從result緩存里獲取
result = decodeJob.decodeResultFromCache();
if (result == null) {
//再?gòu)脑次募彺胬铽@取
result = decodeJob.decodeSourceFromCache();
}
return result;
}
第一次加載顯示decodeResultFromCache會(huì)為空，我們略過(guò),重點(diǎn)看decodeSourceFromCache
public ResourcedecodeSourceFromCache() throws Exception {
//如果不是cacheSource直接返回空
if (!diskCacheStrategy.cacheSource()) {
return null;
}
//...ignore code
}
decode失敗以后會(huì)把EngineRunnable 扔給另外一個(gè)線程
private void onLoadFailed(Exception e) {
if (isDecodingFromCache()) {
stage = Stage.SOURCE;
manager.submitForSource(this);
} else {
manager.onException(e);
}
}
因此它會(huì)再一次走到run()方法里的decode，而此次走的是decodeFromSource
DecodeJob.java
public ResourcedecodeFromSource() throws Exception {
Resourcedecoded = decodeSource();
return transformEncodeAndTranscode(decoded);
}
private ResourcedecodeSource() throws Exception {
Resourcedecoded = null;
try {
// 通過(guò)fetcher去加載Source
final A data = fetcher.loadData(priority);
//...ignore code
decoded = decodeFromSourceData(data);
} finally {
fetcher.cleanup();
}
return decoded;
}
DecodeJob.java
private ResourcedecodeFromSourceData(A data) {
final Resourcedecoded;
if (diskCacheStrategy.cacheSource()) {
decoded = cacheAndDecodeSourceData(data);
} else {
//因?yàn)榫彺娌呗允荝esult，所以走的是該處
decoded = loadProvider.getSourceDecoder().decode(data, width, height);
//...ignore code
}
return decoded;
}
SourceDecode其實(shí)就是ImageVideoBitmapDecoder
public Resourcedecode(ImageVideoWrapper source
, int width, int height){
Resourceresult = null;
InputStream is = source.getStream();
if (is != null) {
//通過(guò)streamDecoder去decode圖，它是StreamBitmapDecoder
result = streamDecoder.decode(is, width, height);
}
if (result == null) {
ParcelFileDescriptor fileDescriptor = source.getFileDescriptor();
if (fileDescriptor != null) {
//通過(guò)fileDescriptorDecoder去decode圖，它是FileDescriptorBitmapDecoder
result = fileDescriptorDecoder.decode(fileDescriptor, width, height);
}
}
return result;
}
ImageVideoBitmapDecoder里有兩種decoder
StreamBitmapDecoder直接將輸入流轉(zhuǎn)成Bitmap
FileDescriptorBitmapDecoder能將流通過(guò)VideoBitmapDecoder去轉(zhuǎn)Bitmap
而VideoBitmapDecoder底層就是通過(guò)MediaMetadataRetriever去獲取第一幀
如果源文件是視頻，它將先通過(guò)StreamBitmapDecoder去decode，結(jié)果decode失敗result=null
然后通過(guò)FileDescriptorBitmapDecoder去decode，可見(jiàn)這里Glide內(nèi)部并不知道源文件是圖片還是視頻，所以先用圖片的方式解
而圖片方式解的時(shí)候也是去讀它的頭文件:
@Override
public Resourcedecode(InputStream source, int width, int height) {
//通過(guò)downsampler去decode
Bitmap bitmap = downsampler.decode(source, bitmapPool, width, height, decodeFormat);
return BitmapResource.obtain(bitmap, bitmapPool);
}
@Override
public Bitmap decode(InputStream is, BitmapPool pool, int outWidth,
int outHeight, DecodeFormat decodeFormat) {
final ByteArrayPool byteArrayPool = ByteArrayPool.get();
final byte[] bytesForOptions = byteArrayPool.getBytes();
final byte[] bytesForStream = byteArrayPool.getBytes();
//此處用了Option池，值得學(xué)習(xí)!
final BitmapFactory.Options options = getDefaultOptions();
//...ignore code
final Bitmap downsampled =
downsampleWithSize(invalidatingStream, bufferedStream,
options, pool, inWidth, inHeight, sampleSize,
decodeFormat);
private static Bitmap decodeStream(MarkEnforcingInputStream is, RecyclableBufferedInputStream bufferedStream,
BitmapFactory.Options options) {
if (options.inJustDecodeBounds) {
is.mark(MARK_POSITION);
} else {
bufferedStream.fixMarkLimit();
}
//如果是視頻文件此處無(wú)法decode出Bitmap
final Bitmap result = BitmapFactory.decodeStream(is, null, options);
//...ignore code
return result;
}
第一種decode失敗會(huì)用第二種，也就是最終會(huì)走到VideoBitmapDecoder去解析
Source緩存策略
如果緩存策略是Source
private ResourcedecodeSource() throws Exception {
Resourcedecoded = null;
try {
final A data = fetcher.loadData(priority);
//...ignore code
decoded = decodeFromSourceData(data);
} finally {
fetcher.cleanup();
}
return decoded;
}
private ResourcedecodeFromSourceData(A data) {
final Resourcedecoded;
//因?yàn)槭蔷彺鍿ource因?yàn)樽遚acheAndDecodeSourceData方法
if (diskCacheStrategy.cacheSource()) {
decoded = cacheAndDecodeSourceData(data);
} else {
long startTime = LogTime.getLogTime();
decoded = loadProvider.getSourceDecoder().decode(data, width, height);
if (Log.isLoggable(TAG, Log.VERBOSE)) {
logWithTimeAndKey("Decoded from source", startTime);
}
}
return decoded;
}
而加載緩存的Decoder是CacheDecoder,非常不幸它不是ImageVideoBitmapDecoder
private ResourceloadFromCache(Key key) {
File cacheFile = diskCacheProvider.getDiskCache().get(key);
if (cacheFile == null) {
return null;
}
Resourceresult = null;
try {
result = loadProvider.getCacheDecoder().decode(cacheFile, width, height);
} finally {
if (result == null) {
diskCacheProvider.getDiskCache().delete(key);
}
}
return result;
}
它是FileToStreamDecoder,以下是截圖
而FileToStreamDecoder的Decoder是StreamBitmapDecoder，最終它是把該文件當(dāng)成圖片解析
因此導(dǎo)致它失敗，如果result==null,它還會(huì)走
diskCacheProvider.getDiskCache().delete(key);
所以如果是視頻流，緩存策略是Source，它會(huì)很讓你失望，不停的copy文件，再解，解失敗再刪除，一直這樣下去
如果該源文件很大，會(huì)影響Glide的性能！
為了驗(yàn)證這一猜想,我們可以通過(guò)抓包工具看一下發(fā)生了什么:
結(jié)果它確實(shí)把這個(gè)視頻存下來(lái)了，不過(guò)發(fā)現(xiàn)decode失敗就會(huì)把它刪除
所以，顯示視頻圖的時(shí)候，一定切記不要用Source緩存策略，它不僅無(wú)法加載成功，而且會(huì)給你帶來(lái)很大隱患
結(jié)束!
總結(jié)
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