Android | Glide細枝篇

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://juejin.im/post/5f0ec887e51d45349917c614","title":""},"content":[{"type":"text","text":"《看完不忘系列》之Glide"}]},{"type":"text","text":" （樹幹篇）一文對"},{"type":"codeinline","content":[{"type":"text","text":"Glide"}]},{"type":"text","text":"加載圖片的核心流程做了介紹，細枝篇作爲補充，將對一些具體實現細節進行深入。本文篇幅略大，大家可以根據目錄索引到感興趣的章節閱讀~"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"源碼基於最新版本"},{"type":"codeinline","content":[{"type":"text","text":"4.11.0"}]},{"type":"text","text":"，先上一張職責圖預覽下，一家人就要整整齊齊~"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/12/123641426bb04181171d0896a24e5d5e.jpeg","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本文約3200字，閱讀大約10分鐘。如個別大圖模糊（官方會壓縮），可前往"},{"type":"link","attrs":{"href":"https://imholiday.cn/","title":""},"content":[{"type":"text","text":"個人站點"}]},{"type":"text","text":"閱讀"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Generated API"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通過創建一些類，繼承相關接口，然後打上註解，由apt來處理這些類，從而實現接口擴展。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"全局配置"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"註解"},{"type":"codeinline","content":[{"type":"text","text":"@GlideModule"}]},{"type":"text","text":"用來配置全局參數和註冊定製的能力，在application裏使用"},{"type":"codeinline","content":[{"type":"text","text":"AppGlideModule"}]},{"type":"text","text":"，在library裏使用"},{"type":"codeinline","content":[{"type":"text","text":"LibraryGlideModule"}]},{"type":"text","text":"，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"@GlideModule\npublic class MyAppGlideModule extends AppGlideModule {\n @Override\n public boolean isManifestParsingEnabled() {\n return false;//新版本不需要解析manifest裏的元數據（沒用過老版本，不太懂，按文檔返回false即可）\n }\n\n @Override\n public void applyOptions(Context context, GlideBuilder builder) {\n super.applyOptions(context, builder);\n //全局配置\n //builder.setBitmapPool(xxx);\n //builder.setDefaultRequestOptions(xxx);\n //...\n }\n\n @Override\n public void registerComponents(Context context, Glide glide, Registry registry) {\n super.registerComponents(context, glide, registry);\n //註冊一些定製的能力，比如擴展新的圖片來源ModelLoader\n //registry.register(xxx);\n }\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"比如現在的"},{"type":"codeinline","content":[{"type":"text","text":"Glide"}]},{"type":"text","text":"的Bitmap默認配置是"},{"type":"codeinline","content":[{"type":"text","text":"ARGB_8888"}]},{"type":"text","text":"，如果項目圖片類型比較單一，不需要透明度通道和高色域，可以配置全局的"},{"type":"codeinline","content":[{"type":"text","text":"RGB_565"}]},{"type":"text","text":"減少一半內存。見"},{"type":"link","attrs":{"href":"https://muyangmin.github.io/glide-docs-cn/doc/configuration.html#%E9%BB%98%E8%AE%A4%E8%AF%B7%E6%B1%82%E9%80%89%E9%A1%B9","title":""},"content":[{"type":"text","text":"默認請求選項"}]},{"type":"text","text":"，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"@GlideModule\npublic class MyAppGlideModule extends AppGlideModule {\n\n @Override\n public void applyOptions(@NonNull Context context, @NonNull GlideBuilder builder) {\n super.applyOptions(context, builder);\n builder.setDefaultRequestOptions(new RequestOptions()\n .format(DecodeFormat.PREFER_RGB_565));\n //注：由於png需要透明度通道，這類圖依舊會採用8888\n }\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"或者可以根據設備評分來衡量，普通機型配置"},{"type":"codeinline","content":[{"type":"text","text":"RGB_565"}]},{"type":"text","text":"（在需要透明度通道的場景局部使用"},{"type":"codeinline","content":[{"type":"text","text":"ARGB_8888"}]},{"type":"text","text":"），高端機型則可以直接配置"},{"type":"codeinline","content":[{"type":"text","text":"ARGB_8888"}]},{"type":"text","text":"，縱享奢華體驗。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/a9/a9847b6e358b20d437b3f2ca8a583456.jpeg","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"行爲打包"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"註解"},{"type":"codeinline","content":[{"type":"text","text":"@GlideExtension"}]},{"type":"text","text":"可以將一些通用行爲打包起來，擴展一個接口方便業務層調用。比如電商App很多頁面都有商品列表，這些商品圖片的寬高如果是固定的，就可以包裝起來，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"@GlideExtension\npublic class MyAppExtension {\n private static final int GOODS_W = 300; //商品圖寬度\n private static final int GOODS_H = 400; //商品圖高度\n\n private MyAppExtension() { //私有化構造方法\n }\n\n @GlideOption\n public static BaseRequestOptions> goods(BaseRequestOptions> options) {\n return options\n .fitCenter()\n .override(GOODS_W, GOODS_H) //寬高\n .placeholder(R.mipmap.ic_launcher) //商品佔位圖\n .error(R.mipmap.ic_launcher); //商品圖加載失敗時\n }\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"rebuild一下項目，生成類"},{"type":"codeinline","content":[{"type":"text","text":"build/generated/ap_generated_sources/debug/out/com/holiday/srccodestudy/glide/GlideOptions.java"}]},{"type":"text","text":"，裏面會多出一個方法，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"class GlideOptions extends RequestOptions implements Cloneable {\n public GlideOptions goods() {\n return (GlideOptions) MyAppExtension.goods(this);\n }\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這時，就可以用goods來直接使用這一組打包好的行爲了，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"//要用GlideApp\nGlideApp.with(this).load(url).goods().into(img);"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"Generated API"}]},{"type":"text","text":"比較適合短週期/小型項目，中大型項目往往不會直接裸使用"},{"type":"codeinline","content":[{"type":"text","text":"Glide"}]},{"type":"text","text":"，會包一箇中間層來進行隔離（禁止業務層用到"},{"type":"codeinline","content":[{"type":"text","text":"Glide"}]},{"type":"text","text":"的任何類），以便隨時可以升級替換，這個中間層就可以根據需要來自行擴展。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"空Fragment取消請求"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Glide.with(context)，當context是Activity時，每個頁面都會被添加一個空fragment，由空fragment持有"},{"type":"codeinline","content":[{"type":"text","text":"頁面級別RequestManager"}]},{"type":"text","text":"來管理請求，那退出頁面時是如何取消請求的呢？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"with通過"},{"type":"codeinline","content":[{"type":"text","text":"RequestManagerRetriever"}]},{"type":"text","text":"獲取"},{"type":"codeinline","content":[{"type":"text","text":"SupportRequestManagerFragment"}]},{"type":"text","text":"，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"//SupportRequestManagerFragment.java\n//創建SupportRequestManagerFragment\npublic SupportRequestManagerFragment() {\n //創建Lifecycle\n this(new ActivityFragmentLifecycle());\n}\n\n//RequestManager.java\n//創建RequestManager，傳入Lifecycle\nRequestManager(\n Glide glide,\n Lifecycle lifecycle,\n //...\n Context context) {\n //lifecycle添加RequestManager爲觀察者\n lifecycle.addListener(this);\n}\n\n//ActivityFragmentLifecycle.java\npublic void addListener(LifecycleListener listener) {\n //記錄觀察者們\n lifecycleListeners.add(listener);\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"退出頁面時，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"//SupportRequestManagerFragment.java\npublic void onDestroy() {\n lifecycle.onDestroy();\n}\n\n//ActivityFragmentLifecycle.java\nvoid onDestroy() {\n for (LifecycleListener lifecycleListener : Util.getSnapshot(lifecycleListeners)) {\n lifecycleListener.onDestroy();\n }\n}\n\n//RequestManager.java\npublic synchronized void onDestroy() {\n //各種取消、註銷操作\n targetTracker.onDestroy();\n for (Target> target : targetTracker.getAll()) {\n clear(target);\n }\n targetTracker.clear();\n requestTracker.clearRequests();\n lifecycle.removeListener(this);\n lifecycle.removeListener(connectivityMonitor);\n mainHandler.removeCallbacks(addSelfToLifecycle);\n glide.unregisterRequestManager(this);\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"代碼看起來有點繞，大致如下圖，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/70/704b49a4432f5fd1f001ffdf7a72c658.jpeg","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Cache緩存"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"內存"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"內存緩存有兩級，一是處於活躍狀態，正被view使用着的緩存，稱"},{"type":"codeinline","content":[{"type":"text","text":"活躍資源"}]},{"type":"text","text":"；二是沒被view使用的，就叫他"},{"type":"codeinline","content":[{"type":"text","text":"非活躍資源"}]},{"type":"text","text":"吧，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"讀取內存："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"//Engine.java\npublic LoadStatus load(...){\n //獲取內存緩存\n memoryResource = loadFromMemory(key, isMemoryCacheable, startTime);\n}\n\nprivate EngineResource> loadFromMemory(\n EngineKey key, boolean isMemoryCacheable, long startTime) {\n\t//活躍資源，從ActiveResources的Map中獲取\n //Map activeEngineResources，值是弱引用，會手動計數\n EngineResource> active = loadFromActiveResources(key);\n if (active != null) {\n return active;\n }\n\t//非活躍資源，從LruResourceCache獲取，也有手動計數\n //返回後，說明這個緩存被view給用上了，非活躍資源則變成活躍\n EngineResource> cached = loadFromCache(key);\n if (cached != null) {\n return cached;\n }\n //內存沒有緩存，load就會去請求\n return null;\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"寫入內存："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"//Engine.java\npublic synchronized void onEngineJobComplete(\n EngineJob> engineJob, Key key, EngineResource> resource) {\n if (resource != null && resource.isMemoryCacheable()) {\n //簡單理解，就是圖片加載完成，這時寫入活躍資源的\n activeResources.activate(key, resource);\n }\n}\n\npublic void onResourceReleased(Key cacheKey, EngineResource> resource) {\n //活躍資源已經沒有被引用了，就移出\n activeResources.deactivate(cacheKey);\n if (resource.isMemoryCacheable()) {\n //轉入非活躍資源\n cache.put(cacheKey, resource);\n }\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如下圖："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/64/64cac3a019594c23e23548956c29329e.jpeg","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"磁盤"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"看看緩存目錄"},{"type":"codeinline","content":[{"type":"text","text":"/data/data/com.holiday.srccodestudy/cache/image_manager_disk_cache/"}]},{"type":"text","text":"，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/3e/3e9d1874af1976767b4299bd97d9dfe3.jpeg","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"先看日誌文件"},{"type":"codeinline","content":[{"type":"text","text":"journal"}]},{"type":"text","text":"，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":""},"content":[{"type":"text","text":"libcore.io.DiskLruCache //頭部名字\n1 //磁盤緩存版本\n1 //App版本\n1 //每個entry（日誌條目）存放的文件數，默認爲1，即一個entry對應一個圖片文件，比如下面就有4個entry，即4張圖片\n\nDIRTY 64d4b00d8ce8b0942d53b3048d5cf6aaa7173acd321e17420891bbc35b98629f\nCLEAN 64d4b00d8ce8b0942d53b3048d5cf6aaa7173acd321e17420891bbc35b98629f 5246\nDIRTY 2c23e32bd9b208092b3cbee8db6f1aff5bc11cb0d4ebd092604ee53099beff37\nCLEAN 2c23e32bd9b208092b3cbee8db6f1aff5bc11cb0d4ebd092604ee53099beff37 404730\nREAD 64d4b00d8ce8b0942d53b3048d5cf6aaa7173acd321e17420891bbc35b98629f\nREAD 2c23e32bd9b208092b3cbee8db6f1aff5bc11cb0d4ebd092604ee53099beff37\nDIRTY b566e62aa0e2fb8cb219ad3aa7a0ade9a96521526501ccd775d70aa4f6489272\nCLEAN b566e62aa0e2fb8cb219ad3aa7a0ade9a96521526501ccd775d70aa4f6489272 9878\nREAD 2c23e32bd9b208092b3cbee8db6f1aff5bc11cb0d4ebd092604ee53099beff37\nREAD b566e62aa0e2fb8cb219ad3aa7a0ade9a96521526501ccd775d70aa4f6489272\nDIRTY 55f4af9c1020e3272ce8063c351aff3518f3a1c9508f38345eab27686e263a4c\nCLEAN 55f4af9c1020e3272ce8063c351aff3518f3a1c9508f38345eab27686e263a4c 69284\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下半部分是操作記錄，行開頭指操作行爲，"},{"type":"codeinline","content":[{"type":"text","text":"DIRTY"}]},{"type":"text","text":"表示在編輯（處於髒數據狀態，別讀），"},{"type":"codeinline","content":[{"type":"text","text":"CLEAN"}]},{"type":"text","text":"（乾淨狀態）表示寫好了，可以讀了，"},{"type":"codeinline","content":[{"type":"text","text":"READ"}]},{"type":"text","text":"表示被讀入了，"},{"type":"codeinline","content":[{"type":"text","text":"REMOVE"}]},{"type":"text","text":"則表示被刪除，中間很長的一串字符就是緩存鍵或文件名字，最後的數字是文件大小，如404730 B=395.2 KB，只有處於"},{"type":"codeinline","content":[{"type":"text","text":"CLEAN"}]},{"type":"text","text":"狀態纔會寫大小。那麼圖中的文件名是什麼意思，爲啥key的後面還有"},{"type":"codeinline","content":[{"type":"text","text":".0"}]},{"type":"text","text":"後綴？因爲一個"},{"type":"codeinline","content":[{"type":"text","text":"entry"}]},{"type":"text","text":"（日誌條目）可以對應多個圖片，"},{"type":"codeinline","content":[{"type":"text","text":".0"}]},{"type":"text","text":"代表"},{"type":"codeinline","content":[{"type":"text","text":"entry"}]},{"type":"text","text":"的第一張圖片，如果有配置1對多，那就會有"},{"type":"codeinline","content":[{"type":"text","text":".1"}]},{"type":"text","text":"、"},{"type":"codeinline","content":[{"type":"text","text":".2"}]},{"type":"text","text":"這樣的後綴。選一個"},{"type":"codeinline","content":[{"type":"text","text":".0"}]},{"type":"text","text":"文件點擊右鍵，"},{"type":"codeinline","content":[{"type":"text","text":"Save as"}]},{"type":"text","text":"保存到電腦，改個jpg後綴，就能看圖了。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"來到"},{"type":"codeinline","content":[{"type":"text","text":"DiskLruCache"}]},{"type":"text","text":"類（看名字知道還是"},{"type":"codeinline","content":[{"type":"text","text":"最近最少使用算法"}]},{"type":"text","text":"），"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"//DiskLruCache.java\n\n//有序Map，實現最近最少使用算法\nprivate final LinkedHashMap lruEntries =\n new LinkedHashMap(0, 0.75f, true);\n\n//讀取磁盤緩存\npublic synchronized Value get(String key) throws IOException {\n //根據key找到entry\n Entry entry = lruEntries.get(key);\n if (entry == null) {\n return null;\n }\n //還不可以讀，返回null\n if (!entry.readable) {\n return null;\n }\n //追加一行日誌：READ\n journalWriter.append(READ);\n journalWriter.append(' ');\n journalWriter.append(key);\n journalWriter.append('\\n');\n //Value就是用來封裝的實體\n return new Value(key, entry.sequenceNumber, entry.cleanFiles, entry.lengths);\n}\n\n//寫入磁盤緩存（這裏只是存進內存的Map，真正的寫入在DiskLruCacheWrapper）\nprivate synchronized Editor edit(String key, long expectedSequenceNumber) throws IOException {\n Entry entry = lruEntries.get(key);\n if (entry == null) {\n entry = new Entry(key);\n //存進LinkedHashMap\n lruEntries.put(key, entry);\n }\n Editor editor = new Editor(entry);\n entry.currentEditor = editor;\n //追加一行日誌：DIRTY\n journalWriter.append(DIRTY);\n return editor;\n}\n\n//刪除磁盤緩存\npublic synchronized boolean remove(String key) throws IOException {\n Entry entry = lruEntries.get(key);\n if (entry == null || entry.currentEditor != null) {\n return false;\n }\n //刪除entry對應的圖片文件\n for (int i = 0; i < valueCount; i++) {\n File file = entry.getCleanFile(i);\n size -= entry.lengths[i];\n entry.lengths[i] = 0;\n }\n //追加一行日誌：REMOVE\n journalWriter.append(REMOVE);\n //從內存Map中移除\n lruEntries.remove(key);\n return true;\n}\n\n//當日志操作數和entry數都達到2000，就清空日誌重寫\nprivate boolean journalRebuildRequired() {\n final int redundantOpCompactThreshold = 2000;\n return redundantOpCount >= redundantOpCompactThreshold //\n && redundantOpCount >= lruEntries.size();\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那麼讀取和寫入時機在哪呢？我們反向追蹤一波"},{"type":"codeinline","content":[{"type":"text","text":"get"}]},{"type":"text","text":"方法，從"},{"type":"codeinline","content":[{"type":"text","text":"DiskLruCache"}]},{"type":"text","text":"到"},{"type":"codeinline","content":[{"type":"text","text":"DiskLruCacheWrapper"}]},{"type":"text","text":"的"},{"type":"codeinline","content":[{"type":"text","text":"get"}]},{"type":"text","text":"，然後再追，發現有兩個類調了"},{"type":"codeinline","content":[{"type":"text","text":"get"}]},{"type":"text","text":"，分別是"},{"type":"codeinline","content":[{"type":"text","text":"DataCacheGenerator"}]},{"type":"text","text":"和"},{"type":"codeinline","content":[{"type":"text","text":"ResourceCacheGenerator"}]},{"type":"text","text":"，前者是原始圖片的緩存，後者是經過"},{"type":"codeinline","content":[{"type":"text","text":"downsampled"}]},{"type":"text","text":"向下採樣或"},{"type":"codeinline","content":[{"type":"text","text":"transformed"}]},{"type":"text","text":"轉換過的圖片，在"},{"type":"link","attrs":{"href":"https://muyangmin.github.io/glide-docs-cn/doc/caching.html#磁盤緩存策略disk-cache-strategy","title":""},"content":[{"type":"text","text":"磁盤緩存策略"}]},{"type":"text","text":"中提到："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"目前支持的策略允許你阻止加載過程使用或寫入磁盤緩存，選擇性地僅緩存無修改的原生數據，或僅緩存變換過的縮略圖，或是兼而有之。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"默認情況下，網絡圖片緩存的是原始數據，那我們繼續跟"},{"type":"codeinline","content":[{"type":"text","text":"DataCacheGenerator"}]},{"type":"text","text":"，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"//DataCacheGenerator.java\npublic boolean startNext() {\n while (modelLoaders == null || !hasNextModelLoader()) {\n sourceIdIndex++;\n if (sourceIdIndex >= cacheKeys.size()) {\n return false;\n }\n Key sourceId = cacheKeys.get(sourceIdIndex);\n Key originalKey = new DataCacheKey(sourceId, helper.getSignature());\n //獲取磁盤緩存的圖片文件\n cacheFile = helper.getDiskCache().get(originalKey);\n if (cacheFile != null) {\n this.sourceKey = sourceId;\n //獲取能夠處理File類型的modelLoaders集合，\n //modelLoader就是圖片加載類型，比如網絡url、本地Uri、文件File都有各自的loader\n modelLoaders = helper.getModelLoaders(cacheFile);\n modelLoaderIndex = 0;\n }\n }\n loadData = null;\n boolean started = false;\n while (!started && hasNextModelLoader()) {\n //成功找到ByteBufferFileLoader，可以處理File\n ModelLoader modelLoader = modelLoaders.get(modelLoaderIndex++);\n //傳入磁盤緩存的圖片文件cacheFile\n loadData =\n modelLoader.buildLoadData(\n cacheFile, helper.getWidth(), helper.getHeight(), helper.getOptions());\n if (loadData != null && helper.hasLoadPath(loadData.fetcher.getDataClass())) {\n started = true;\n loadData.fetcher.loadData(helper.getPriority(), this);\n }\n }\n return started;\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"繼續跟"},{"type":"codeinline","content":[{"type":"text","text":"modelLoader.buildLoadData"}]},{"type":"text","text":"，後邊就是把圖片文件cacheFile封裝成"},{"type":"codeinline","content":[{"type":"text","text":"ByteBufferFetcher"}]},{"type":"text","text":"，然後調用上邊的"},{"type":"codeinline","content":[{"type":"text","text":"loadData.fetcher.loadData"}]},{"type":"text","text":"進行回調，就不繼續跟了，"},{"type":"codeinline","content":[{"type":"text","text":"startNext"}]},{"type":"text","text":"方法在"},{"type":"codeinline","content":[{"type":"text","text":"DecodeJob"}]},{"type":"text","text":"裏會被調用，樹幹篇中可知他就是圖片加載過程用到的一個Runnable，好了，下面看看緩存寫入時機，反向追蹤"},{"type":"codeinline","content":[{"type":"text","text":"edit"}]},{"type":"text","text":"方法，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"//DiskLruCacheWrapper.java\npublic void put(Key key, Writer writer) {\n String safeKey = safeKeyGenerator.getSafeKey(key);\n writeLocker.acquire(safeKey);\n try {\n try {\n DiskLruCache diskCache = getDiskCache();\n Value current = diskCache.get(safeKey);\n //已經有緩存，結束\n if (current != null) {\n return;\n }\n\t\t\t//獲取Editor\n DiskLruCache.Editor editor = diskCache.edit(safeKey);\n try {\n File file = editor.getFile(0);\n if (writer.write(file)) {//編碼寫入文件\n //提交“事務”，追加一行日誌：CLEAN，表示該條目對應的緩存文件已經乾淨可以使用了\n editor.commit();\n }\n } finally {\n editor.abortUnlessCommitted();\n }\n } catch (IOException e) {\n }\n } finally {\n writeLocker.release(safeKey);\n }\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"同樣，"},{"type":"codeinline","content":[{"type":"text","text":"put"}]},{"type":"text","text":"方法也會在"},{"type":"codeinline","content":[{"type":"text","text":"DecodeJob"}]},{"type":"text","text":"裏被調用，就不往上跟了。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/2c/2c2fb30fb1bc2d171672bbe8c5880173.jpeg","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"合併內存緩存和磁盤緩存，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/bd/bd182445a818a06d627c900b4fdb5900.jpeg","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"BitmapPool令人詬病"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"Glide"}]},{"type":"text","text":"有將Bitmap進行池化，默認是"},{"type":"codeinline","content":[{"type":"text","text":"LruBitmapPool"}]},{"type":"text","text":"，他會決定怎麼複用Bitmap、何時回收Bitmap、池子上限時清理，也就是說，他全盤接管了Bitmap的處理，如果項目中有"},{"type":"codeinline","content":[{"type":"text","text":"在回調方法外持有Bitmap"}]},{"type":"text","text":"、"},{"type":"codeinline","content":[{"type":"text","text":"手動回收Bitmap"}]},{"type":"text","text":"的場景，會發生意料外的crash，詳見"},{"type":"link","attrs":{"href":"https://muyangmin.github.io/glide-docs-cn/doc/resourcereuse.html#資源重用錯誤的徵兆","title":""},"content":[{"type":"text","text":"資源重用錯誤的徵兆"}]},{"type":"text","text":"。即，我們要有這樣的意識，既然使用了"},{"type":"codeinline","content":[{"type":"text","text":"Glide"}]},{"type":"text","text":"，就不要再關心Bitmap的事情了，全盤交由"},{"type":"codeinline","content":[{"type":"text","text":"BitmapPool"}]},{"type":"text","text":"管理即可。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"發散：所謂池化，就是設計模式中的享元模式，即維護一個有限個數的對象池來實現對象複用，從而避免頻繁的創建銷燬對象。比如Handler消息機制中的"},{"type":"codeinline","content":[{"type":"text","text":"Message.obtain"}]},{"type":"text","text":"，就是從消息池（鏈表）裏取出對象來複用，池子的消息總數被限制在MAX"},{"type":"text","marks":[{"type":"italic"}],"text":"POOL"},{"type":"text","text":"SIZE=50。Android內的很多實現都是基於Handler（消息驅動）的，池化能減少很大部分的創建銷燬。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Decoder解碼"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"鏈路有點長，直接看調用棧，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c3/c31785bffa628b504e0e2190fb60eadb.jpeg","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可見最終走的是native層的"},{"type":"codeinline","content":[{"type":"text","text":"nativeDecodeStream"}]},{"type":"text","text":"，哈迪就不跟了，對inputstream轉成bitmap感興趣的讀者自行研究啦~"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/0b/0ba09e821484cd12c9c21b9af1621b4e.jpeg","alt":null,"title":"","style":[{"key":"width","value":"50%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"總結"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"Glide"}]},{"type":"text","text":"有如下優勢："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":"1","normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"空Fragment感知頁面生命週期，避免無效請求"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"高度可配置，詳見"},{"type":"link","attrs":{"href":"https://muyangmin.github.io/glide-docs-cn/doc/configuration.html","title":""},"content":[{"type":"text","text":"配置"}]}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"三級緩存（網絡層緩存如okhttp就不考慮了）：內存活躍資源"},{"type":"codeinline","content":[{"type":"text","text":"ActiveResources"}]},{"type":"text","text":"、內存非活躍資源"},{"type":"codeinline","content":[{"type":"text","text":"LruResourceCache"}]},{"type":"text","text":"、磁盤緩存"},{"type":"codeinline","content":[{"type":"text","text":"DiskLruCache"}]}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"可定製，引入apt處理註解，打包行爲，擴展接口。（哈迪沒怎麼用，感覺有點雞肋，可能以後會真香）"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":5,"align":null,"origin":null},"content":[{"type":"text","text":"可擴展，可以替換網絡層、定製自己的圖片來源"},{"type":"codeinline","content":[{"type":"text","text":"ModelLoader"}]},{"type":"text","text":"，詳見"},{"type":"link","attrs":{"href":"https://muyangmin.github.io/glide-docs-cn/tut/custom-modelloader.html","title":""},"content":[{"type":"text","text":"編寫定製的ModelLoader"}]}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":6,"align":null,"origin":null},"content":[{"type":"text","text":"無侵入，into可以傳入最簡單的ImageView"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":7,"align":null,"origin":null},"content":[{"type":"text","text":"優秀的設計模式運用、應用層優雅的鏈式調用"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"至於缺點吧，暫時還沒想到。本文只列出了哈迪覺得比較精彩的細節，可能還有遺漏的一些點，大家有補充的可以留下評論，後續我會更新進本文。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"參考資料"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"https://muyangmin.github.io/glide-docs-cn/","title":""},"content":[{"type":"text","text":"官方文檔"}]},{"type":"text","text":" & "},{"type":"link","attrs":{"href":"https://github.com/bumptech/glide","title":""},"content":[{"type":"text","text":"GitHub"}]}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"horizontalrule"},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/18/18280df97439e1bea7bded6864c8a8a8.jpeg","alt":null,"title":"","style":[{"key":"width","value":"25%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}