Glide初始化,采用懶注冊(cè)的方式跺讯，設(shè)置參數(shù)

Glide是一個(gè)單例，應(yīng)用第一次使用Glide是會(huì)調(diào)用initializeGlide方法殉农，編譯期根據(jù)GlideModule或清單文件中的模塊命名（已棄用）生成GeneratedAppGlideModuleImpl類刀脏，提供初始化構(gòu)造參數(shù)的方法填充GlideBuilder，最終build出Glide
GlideModule注解類,提供初始化默認(rèn)參數(shù)修改超凳，AppGlideModule提供兩個(gè)方法

• isManifestParsingEnabled 是否讀取清單文件中的參數(shù)
• applyOptions 修改GlideBuilder的默認(rèn)初始化參數(shù)愈污，設(shè)置緩存參數(shù)之類
  使用方法是新建類繼承這個(gè)類并且加上GlideModule注解，按照需要重寫上面兩個(gè)方法完成初始化參數(shù)設(shè)置

/**
Defines a set of dependencies and options to use when initializing Glide within an application.
...
*/
public abstract class AppGlideModule extends LibraryGlideModule implements AppliesOptions {
  /**
   * Returns {@code true} if Glide should check the AndroidManifest for {@link GlideModule}s.
   *
   * <p>Implementations should return {@code false} after they and their dependencies have migrated
   * to Glide's annotation processor.
   *
   * <p>Returns {@code true} by default.
   */
  public boolean isManifestParsingEnabled() {
    return true;
  }

  @Override
  public void applyOptions(@NonNull Context context, @NonNull GlideBuilder builder) {
    // Default empty impl.
  }
}

/**
 * Registers a set of components to use when initializing Glide within an app when
*/
public abstract class LibraryGlideModule implements RegistersComponents {
  @Override
  public void registerComponents(@NonNull Context context, @NonNull Glide glide,
      @NonNull Registry registry) {
    // Default empty impl.
  }
}

registerComponents可增加解析組件
例子：增加webp格式的圖片加載

@GlideModule
public class WebpGlideLibraryModule extends LibraryGlideModule {

    @Override
    public void registerComponents(Context context, Glide glide, Registry registry) {

        // We should put our decoder before the build-in decoders,
        // because the Downsampler will consume arbitrary data and make the inputstream corrupt
        // on some devices
        final Resources resources = context.getResources();
        final BitmapPool bitmapPool = glide.getBitmapPool();
        final ArrayPool arrayPool = glide.getArrayPool();
        /* static webp decoders */
        WebpDownsampler webpDownsampler = new WebpDownsampler(registry.getImageHeaderParsers(),
                resources.getDisplayMetrics(), bitmapPool, arrayPool);
        AnimatedWebpBitmapDecoder bitmapDecoder = new AnimatedWebpBitmapDecoder(arrayPool, bitmapPool);
        ByteBufferBitmapWebpDecoder byteBufferBitmapDecoder = new ByteBufferBitmapWebpDecoder(webpDownsampler);
        StreamBitmapWebpDecoder streamBitmapDecoder = new StreamBitmapWebpDecoder(webpDownsampler, arrayPool);
        /* animate webp decoders */
        ByteBufferWebpDecoder byteBufferWebpDecoder =
                new ByteBufferWebpDecoder(context, arrayPool, bitmapPool);
        registry
                /* Bitmaps for static webp images */
                .prepend(Registry.BUCKET_BITMAP, ByteBuffer.class, Bitmap.class, byteBufferBitmapDecoder)
                .prepend(Registry.BUCKET_BITMAP, InputStream.class, Bitmap.class, streamBitmapDecoder)
                /* BitmapDrawables for static webp images */
                .prepend(
                        Registry.BUCKET_BITMAP_DRAWABLE,
                        ByteBuffer.class,
                        BitmapDrawable.class,
                        new BitmapDrawableDecoder<>(resources, byteBufferBitmapDecoder))
                .prepend(
                        Registry.BUCKET_BITMAP_DRAWABLE,
                        InputStream.class,
                        BitmapDrawable.class,
                        new BitmapDrawableDecoder<>(resources, streamBitmapDecoder))
                /* Bitmaps for animated webp images*/
                .prepend(Registry.BUCKET_BITMAP, ByteBuffer.class, Bitmap.class,
                        new ByteBufferAnimatedBitmapDecoder(bitmapDecoder))
                .prepend(Registry.BUCKET_BITMAP, InputStream.class, Bitmap.class,
                        new StreamAnimatedBitmapDecoder(bitmapDecoder))
                /* Animated webp images */
                .prepend(ByteBuffer.class, WebpDrawable.class, byteBufferWebpDecoder)
                .prepend(InputStream.class, WebpDrawable.class, new StreamWebpDecoder(byteBufferWebpDecoder, arrayPool))
                .prepend(WebpDrawable.class, new WebpDrawableEncoder());
    }
}

3級(jí)緩存結(jié)構(gòu)

緩存優(yōu)先級(jí) ActiveResources轮傍，MemoryCache暂雹，DiskCache
從最終的load方法可以看出，加載會(huì)先取ActiveResources创夜，再取MemoryCache如果有的話會(huì)從MemoryCache中刪除并且添加到ActiveResources中杭跪，最后創(chuàng)建EngineJob異步取本地緩存或網(wǎng)絡(luò)獲取，獲取成功后會(huì)添加到ActiveResources中驰吓，ActiveResources利用ReferenceQueue在弱應(yīng)用被回收時(shí)從ActiveResources中移除并添加到MemoryCache中涧尿。

  public <R> LoadStatus load(...) {
    ...
    EngineResource<?> active = loadFromActiveResources(key, isMemoryCacheable);
    if (active != null) {
      cb.onResourceReady(active, DataSource.MEMORY_CACHE);
      if (VERBOSE_IS_LOGGABLE) {
        logWithTimeAndKey("Loaded resource from active resources", startTime, key);
      }
      return null;
    }

    EngineResource<?> cached = loadFromCache(key, isMemoryCacheable);
    if (cached != null) {
      cb.onResourceReady(cached, DataSource.MEMORY_CACHE);
      if (VERBOSE_IS_LOGGABLE) {
        logWithTimeAndKey("Loaded resource from cache", startTime, key);
      }
      return null;
    }

    EngineJob<?> current = jobs.get(key, onlyRetrieveFromCache);
    if (current != null) {
      current.addCallback(cb);
      if (VERBOSE_IS_LOGGABLE) {
        logWithTimeAndKey("Added to existing load", startTime, key);
      }
      return new LoadStatus(cb, current);
    }

    EngineJob<R> engineJob =
        engineJobFactory.build(...);

    DecodeJob<R> decodeJob =
        decodeJobFactory.build(...);

    jobs.put(key, engineJob);

    engineJob.addCallback(cb);
    engineJob.start(decodeJob);

    if (VERBOSE_IS_LOGGABLE) {
      logWithTimeAndKey("Started new load", startTime, key);
    }
    return new LoadStatus(cb, engineJob);
  }

• ActiveResources可以理解為是當(dāng)前正在被引用的資源弱引用（WeakReference）
• MemoryCache是內(nèi)存緩存，可設(shè)置大小限制檬贰，不會(huì)包含ActiveResources中的資源
• DiskCache 本地文件緩存姑廉，可設(shè)置緩存路徑及緩存文件總大小
• 這里有個(gè)細(xì)節(jié)，為什么要有兩個(gè)內(nèi)存緩存翁涤，原因是MemoryCache是有大小限制的桥言，為防止正在使用的緩存被釋放，所以增加了ActiveResources
  DiskCache本地緩存迷雪，首次獲取本地緩存時(shí)會(huì)觸發(fā)本地文件緩存掃描限书，緩存目錄會(huì)有一個(gè)journal文件
  里面記錄了本地緩存文件列表及信息,如下

libcore.io.DiskLruCache
1
1
1

CLEAN b31dfe4cd710e8868de840b27c2feba6443539b378343717c28174c5ff4c3a51 8318
CLEAN 3802507bffb423d3e9455801d15a5d82937e505f82134e0675e3096ecadbea5b 10414
CLEAN 28e5a4b66341ef88252f41602144354db0aa878c1863262e9950559df4488a1f 15396

  private void readJournal() throws IOException {
    StrictLineReader reader = new StrictLineReader(new FileInputStream(journalFile), Util.US_ASCII);
    try {
      String magic = reader.readLine();
      String version = reader.readLine();
      String appVersionString = reader.readLine();
      String valueCountString = reader.readLine();
      String blank = reader.readLine();
      if (!MAGIC.equals(magic)
          || !VERSION_1.equals(version)
          || !Integer.toString(appVersion).equals(appVersionString)
          || !Integer.toString(valueCount).equals(valueCountString)
          || !"".equals(blank)) {
        throw new IOException("unexpected journal header: [" + magic + ", " + version + ", "
            + valueCountString + ", " + blank + "]");
      }
      ...
  }

journal文件前5行目前來(lái)看只是起到了判斷文件是否是glide緩存目錄文件的一個(gè)規(guī)則，后面才是緩存文件信息章咧，以空格分開,分別是文件狀態(tài)/文件名/文件大小倦西，目前來(lái)看只有CLEAN狀態(tài)的文件才有文件大小信息
文件狀態(tài)有

  private static final String CLEAN = "CLEAN"; //干凈的數(shù)據(jù)
  private static final String DIRTY = "DIRTY";  //臟數(shù)據(jù)，可能正在被修改
  private static final String REMOVE = "REMOVE"; //已被刪除
  private static final String READ = "READ";  //正在被讀取

文件名有后綴赁严，journal文件中文件名信息并不完整扰柠，可能考慮以后緩存多分文件所以是以name.0開始命名
緩存文件。

    private Entry(String key) {
      this.key = key;
      this.lengths = new long[valueCount];
      cleanFiles = new File[valueCount];
      dirtyFiles = new File[valueCount];

      // The names are repetitive so re-use the same builder to avoid allocations.
      StringBuilder fileBuilder = new StringBuilder(key).append('.');
      int truncateTo = fileBuilder.length();
      for (int i = 0; i < valueCount; i++) {
          fileBuilder.append(i);
          cleanFiles[i] = new File(directory, fileBuilder.toString());
          fileBuilder.append(".tmp");
          dirtyFiles[i] = new File(directory, fileBuilder.toString());
          fileBuilder.setLength(truncateTo);
      }
    }

Glide的生命周期

Glide通過(guò)with(context)的方法創(chuàng)建一個(gè)RequestManager疼约，這里要說(shuō)的就是這個(gè)manager的生命周期卤档，

  @NonNull
  public RequestManager get(@NonNull Context context) {
    if (context == null) {
      throw new IllegalArgumentException("You cannot start a load on a null Context");
    } else if (Util.isOnMainThread() && !(context instanceof Application)) {
      if (context instanceof FragmentActivity) {
        return get((FragmentActivity) context);
      } else if (context instanceof Activity) {
        return get((Activity) context);
      } else if (context instanceof ContextWrapper) {
        return get(((ContextWrapper) context).getBaseContext());
      }
    }

    return getApplicationManager(context);
  }

如上代碼如果context是Application，則生命跟隨進(jìn)程程剥，若為Activity或FragmentActivity劝枣，則會(huì)創(chuàng)建一個(gè)空SupportRequestManagerFragment加到Activity中，監(jiān)聽activity的生命周期

  private RequestManager supportFragmentGet(
      @NonNull Context context,
      @NonNull FragmentManager fm,
      @Nullable Fragment parentHint,
      boolean isParentVisible) {
    SupportRequestManagerFragment current =
        getSupportRequestManagerFragment(fm, parentHint, isParentVisible);
    RequestManager requestManager = current.getRequestManager();
    if (requestManager == null) {
      // TODO(b/27524013): Factor out this Glide.get() call.
      Glide glide = Glide.get(context);
      requestManager =
          factory.build(
              glide, current.getGlideLifecycle(), current.getRequestManagerTreeNode(), context);
      current.setRequestManager(requestManager);
    }
    return requestManager;
  }

由此即綁定了RequestManager與context的生命周期，發(fā)生變化后會(huì)通知給RequestManager中的Request和Target

  @Override
  public void onStart() {
    resumeRequests();
    targetTracker.onStart();
  }

  /**
   * Lifecycle callback that unregisters for connectivity events (if the
   * android.permission.ACCESS_NETWORK_STATE permission is present) and pauses in progress loads.
   */
  @Override
  public void onStop() {
    pauseRequests();
    targetTracker.onStop();
  }

  /**
   * Lifecycle callback that cancels all in progress requests and clears and recycles resources for
   * all completed requests.
   */
  @Override
  public void onDestroy() {
    targetTracker.onDestroy();
    for (Target<?> target : targetTracker.getAll()) {
      clear(target);
    }
    targetTracker.clear();
    requestTracker.clearRequests();
    lifecycle.removeListener(this);
    lifecycle.removeListener(connectivityMonitor);
    mainHandler.removeCallbacks(addSelfToLifecycle);
    glide.unregisterRequestManager(this);
  }

以此實(shí)現(xiàn)請(qǐng)求的暫停/繼續(xù)與結(jié)束舔腾，該功能為我們實(shí)現(xiàn)滑動(dòng)時(shí)暫停圖片加載提供基礎(chǔ)幫助溪胶。