Glide原始碼分析

摘要： 版本4.9.0 問題 Glide如何實現與生命週期的繫結？ Glide如何實現快取？ Glide如何實現圖片壓縮? Glide如何實現與生命週期的繫結? 建立RequestManger,將其與with()傳入 Activity, Fragm...

版本4.9.0

問題

• Glide如何實現與生命週期的繫結？
• Glide如何實現快取？
• Glide如何實現圖片壓縮?

Glide如何實現與生命週期的繫結?

建立RequestManger,將其與with()傳入 Activity, Fragment的生命週期繫結,

這樣做的好處是當Activity/Fragment stop/destroy時，RequestManager也會做相應操作，如停掉圖片載入

• 繫結Application Context

  首先無論with()傳入的是什麼，只要是在子執行緒中呼叫,建立的RequestManger與Application Context繫結，這樣建立的RequestMangager的生命週期與

  if (Util.isOnBackgroundThread()) {
  return get(fragment.getActivity().getApplicationContext());
  } else {
  ... ...
  }

  這樣做的目的是防止Activity,Fragment記憶體洩漏

• Activity與FramgentActivity

  class RequestManagerFragment {
  ... ...
  private final ActivityFragmentLifecycle lifecycle;
  
  @Override
  public void onStart() {
  super.onStart();
  lifecycle.onStart();
  }
  @Override
  public void onStop() {
  super.onStop();
  lifecycle.onStop();
  }
  
  @Override
  public void onDestroy() {
  super.onDestroy();
  lifecycle.onDestroy();
  unregisterFragmentWithRoot();
  }
  ... ...
  }

  class ActivityFragmentLifecycle implements Lifecycle {
  @Override
  public void addListener(@NonNull LifecycleListener listener) {
  lifecycleListeners.add(listener);
  
  if (isDestroyed) {
  listener.onDestroy();
  } else if (isStarted) {
  listener.onStart();
  } else {
  listener.onStop();
  }
  }
  void onStart() {
  isStarted = true;
  for (LifecycleListener lifecycleListener :Util.getSnapshot(lifecycleListeners)) {
  lifecycleListener.onStart();
  }
  }
  
  void onStop() {
  isStarted = false;
  for (LifecycleListener lifecycleListener :Util.getSnapshot(lifecycleListeners)) {
  lifecycleListener.onStop();
  }
  }
  
  void onDestroy() {
  isDestroyed = true;
  for (LifecycleListener lifecycleListener :Util.getSnapshot(lifecycleListeners)) {
  lifecycleListener.onDestroy();
  }
  }
  }

  RequestManagerFragment current = getRequestManagerFragment(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);
  }

  RequestManagerFragment中建立了並對外提供ActivityFragmentLifecycle物件,

  建立RequestManager時，傳入ActivityFragmentLifecycle物件

  RequestManager(
  Glide glide,
  Lifecycle lifecycle,
  RequestManagerTreeNode treeNode,
  RequestTracker requestTracker,
  ConnectivityMonitorFactory factory,
  Context context) {
  
  ... ...
  lifecycle.addListener(this); 
  ... ...
  }
  
  @Override
  public synchronized void onStart() {
  resumeRequests();
  targetTracker.onStart();
  }
  @Override
  public synchronized void onStop() {
  pauseRequests();
  targetTracker.onStop();
  }
  @Override
  public synchronized 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);
  }

  這樣RequestManger.onStart(),onStop(),onDestroy()與Activity的生命週期通過Activity繫結的空Fragment實現了繫結

• Fragment

  與Activity的繫結方式類似，

  FragmentManager fm = fragment.getChildFragmentManager();

  將RequestManger.onStart(),onStop(),onDestroy()與Fragment的生命週期通過Fragment繫結的空Fragment實現的繫結

• View

  通過View可以獲取它所在的Activity 或 Fragment

  Activity activity = findActivity(view.getContext());
  
  @Nullable
  private Activity findActivity(@NonNull Context context) {
  if (context instanceof Activity) {
  return (Activity) context;
  } else if (context instanceof ContextWrapper) {
  return findActivity(((ContextWrapper) context).getBaseContext());
  } else {
  return null;
  }
  }
  
  @Nullable
  private Fragment findSupportFragment(@NonNull View target, @NonNull
  FragmentActivity activity) {
  
  tempViewToSupportFragment.clear();
  findAllSupportFragmentsWithViews(
  activity.getSupportFragmentManager().getFragments(), tempViewToSupportFragment);
  Fragment result = null;
  View activityRoot = activity.findViewById(android.R.id.content);
  View current = target;
  while (!current.equals(activityRoot)) {
  result = tempViewToSupportFragment.get(current);
  if (result != null) {
  break;
  }
  if (current.getParent() instanceof View) {
  current = (View) current.getParent();
  } else {
  break;
  }
  }
  
  tempViewToSupportFragment.clear();
  return result;
  }

• Context

  通過Context獲取Activity or FragmentActivity or Application Context

  if (context == null) {
  throw new IllegalArgumentException("You cannot start a load on anullContext");
  } 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);

Glide如何實現快取？

• 提供了兩個記憶體快取,分別儲存強弱引用

  弱引用的快取: 存放正在使用的

  強引用的快取: 存放沒有使用的

  Map<Key, ResourceWeakReference> activeEngineResources//在
  private final Map<T, Y> cache = new LinkedHashMap<>(100, 0.75f, true);//在LruCache類中

  查詢記憶體快取，

  1.先從弱引用的快取查，
  2.沒有再從強引用的快取查，查到後從強引用快取中移除，加入到弱引用的快取

  Engine.load()方法

  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);

  Engine.loadFromCache()方法

  private EngineResource<?> loadFromCache(Key key, boolean isMemoryCacheable) {
  if (!isMemoryCacheable) {
  return null;
  }
  
  EngineResource<?> cached = getEngineResourceFromCache(key); //
  if (cached != null) {
  cached.acquire();
  activeResources.activate(key, cached);
  }
  return cached;
  }
  
  private EngineResource<?> getEngineResourceFromCache(Key key) {
  Resource<?> cached = cache.remove(key);
  final EngineResource<?> result;
  if (cached == null) {
  result = null;
  } else if (cached instanceof EngineResource) {
  // Save an object allocation if we've cached an EngineResource (the typical case).
  result = (EngineResource<?>) cached;
  } else {
  result = new EngineResource<>(cached, true /*isMemoryCacheable*/, true /*isRecyclable*/);
  }
  return result;
  }

Glide如何實現圖片壓縮?

Glide實現的等比壓縮，保持原圖長寬比例，主要是通過原圖寬高和預設的寬高設定BitmapFactory.Options.inSampleSize

float widthPercentage = requestedWidth / (float) sourceWidth;
float heightPercentage = requestedHeight / (float) sourceHeight;
exactScaleFactor = Math.min(widthPercentage, heightPercentage);
int outWidth = round(exactScaleFactor * sourceWidth);
int outHeight = round(exactScaleFactor * sourceHeight);

int widthScaleFactor = sourceWidth / outWidth;
int heightScaleFactor = sourceHeight / outHeight;

int scaleFactor = rounding == SampleSizeRounding.MEMORY
? Math.max(widthScaleFactor, heightScaleFactor)
: Math.min(widthScaleFactor, heightScaleFactor);

int powerOfTwoSampleSize;
// BitmapFactory does not support downsampling wbmp files on platforms <= M. See b/27305903.
if (Build.VERSION.SDK_INT <= 23
&& NO_DOWNSAMPLE_PRE_N_MIME_TYPES.contains(options.outMimeType)) {
powerOfTwoSampleSize = 1;
} else {
powerOfTwoSampleSize = Math.max(1, Integer.highestOneBit(scaleFactor));
if (rounding == SampleSizeRounding.MEMORY
&& powerOfTwoSampleSize < (1.f / exactScaleFactor)) {
powerOfTwoSampleSize = powerOfTwoSampleSize << 1;
}
}
options.inSampleSize = powerOfTwoSampleSize;