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@act262 2017-06-01T08:52:07.000000Z 字数 7016 阅读 1232

Drawable资源的加载流程

Android_Drawable

API24+开始对Drawable的内部加载流程有所变动，但在Resources的调用表现接口不变。

以下基于API 25的SDK源码分析

基本流程如下：

Resources#getDrawable -> ResourcesImpl#loadDrawable -> ResourcesImpl#loadDrawableForCookie -> Drawable#createFromXml
-> Drawable#createFromXmlInner -> Resources#getDrawableInflater -> DrawableInflater#inflateFromXml

ResourcesImpl#loadDrawable

  1. Drawable loadDrawable(Resources wrapper, TypedValue value, int id, Resources.Theme theme, boolean useCache) throws NotFoundException {
  2.         try {
  3.             if (TRACE_FOR_PRELOAD) {
  4.                 // Log only framework resources
  5.                 if ((id >>> 24) == 0x1) {
  6.                     final String name = getResourceName(id);
  7.                     if (name != null) {
  8.                         Log.d("PreloadDrawable", name);
  9.                     }
  10.                 }
  11.             }
  13.             final boolean isColorDrawable;
  14.             final DrawableCache caches;
  15.             final long key;
  16.             // 区分普通Drawable还是ColorDrawable
  17.             if (value.type >= TypedValue.TYPE_FIRST_COLOR_INT
  18.                     && value.type <= TypedValue.TYPE_LAST_COLOR_INT) {
  19.                 isColorDrawable = true;
  20.                 caches = mColorDrawableCache;
  21.                 key = value.data;
  22.             } else {
  23.                 isColorDrawable = false;
  24.                 caches = mDrawableCache;
  25.                 key = (((long) value.assetCookie) << 32) | value.data;
  26.             }
  28.             // First, check whether we have a cached version of this drawable
  29.             // that was inflated against the specified theme. Skip the cache if
  30.             // we're currently preloading or we're not using the cache.
  31.             if (!mPreloading && useCache) {
  32.                 final Drawable cachedDrawable = caches.getInstance(key, wrapper, theme);
  33.                 if (cachedDrawable != null) {
  34.                     return cachedDrawable;
  35.                 }
  36.             }
  38.             // Next, check preloaded drawables. Preloaded drawables may contain
  39.             // unresolved theme attributes.
  40.             // 从预加载的缓存中获取ConstantState
  41.             final Drawable.ConstantState cs;
  42.             if (isColorDrawable) {
  43.                 cs = sPreloadedColorDrawables.get(key);
  44.             } else {
  45.                 cs = sPreloadedDrawables[mConfiguration.getLayoutDirection()].get(key);
  46.             }
  48.             // 使用缓存已有的ConstantState new出Drawable,复用ConstantState
  49.             Drawable dr;
  50.             if (cs != null) {
  51.                 dr = cs.newDrawable(wrapper);
  52.             } else if (isColorDrawable) {
  53.                 dr = new ColorDrawable(value.data);
  54.             } else {
  55.                 // 缓存没有找到则是0开始加载进来
  56.                 dr = loadDrawableForCookie(wrapper, value, id, null);
  57.             }
  59.             // Determine if the drawable has unresolved theme attributes. If it
  60.             // does, we'll need to apply a theme and store it in a theme-specific
  61.             // cache.
  62.             final boolean canApplyTheme = dr != null && dr.canApplyTheme();
  63.             if (canApplyTheme && theme != null) {
  64.                 dr = dr.mutate();
  65.                 dr.applyTheme(theme);
  66.                 dr.clearMutated();
  67.             }
  69.             // If we were able to obtain a drawable, store it in the appropriate
  70.             // cache: preload, not themed, null theme, or theme-specific. Don't
  71.             // pollute the cache with drawables loaded from a foreign density.
  72.             if (dr != null && useCache) {
  73.                 // 缓存起来 
  74.                 dr.setChangingConfigurations(value.changingConfigurations);
  75.                 cacheDrawable(value, isColorDrawable, caches, theme, canApplyTheme, key, dr);
  76.             }
  78.             return dr;
  79.         } catch (Exception e) {
  80.             String name;
  81.             try {
  82.                 name = getResourceName(id);
  83.             } catch (NotFoundException e2) {
  84.                 name = "(missing name)";
  85.             }
  87.         // The target drawable might fail to load for any number of
  88.         // reasons, but we always want to include the resource name.
  89.         // Since the client already expects this method to throw a
  90.         // NotFoundException, just throw one of those.
  91.         final NotFoundException nfe = new NotFoundException("Drawable " + name
  92.                 + " with resource ID #0x" + Integer.toHexString(id), e);
  93.         nfe.setStackTrace(new StackTraceElement[0]);
  94.         throw nfe;
  95.     }
  96. }

ResourcesImpl#loadDrawableForCookie

  1. private Drawable loadDrawableForCookie(Resources wrapper, TypedValue value, int id,
  2.             Resources.Theme theme) {
  3.         if (value.string == null) {
  4.             throw new NotFoundException("Resource \"" + getResourceName(id) + "\" ("
  5.                     + Integer.toHexString(id) + ") is not a Drawable (color or path): " + value);
  6.         }
  8.         final String file = value.string.toString();
  10.         if (TRACE_FOR_MISS_PRELOAD) {
  11.             // Log only framework resources
  12.             if ((id >>> 24) == 0x1) {
  13.                 final String name = getResourceName(id);
  14.                 if (name != null) {
  15.                     Log.d(TAG, "Loading framework drawable #" + Integer.toHexString(id)
  16.                             + ": " + name + " at " + file);
  17.                 }
  18.             }
  19.         }
  21.         if (DEBUG_LOAD) {
  22.             Log.v(TAG, "Loading drawable for cookie " + value.assetCookie + ": " + file);
  23.         }
  25.         final Drawable dr;
  27.         Trace.traceBegin(Trace.TRACE_TAG_RESOURCES, file);
  28.         try {
  29.             if (file.endsWith(".xml")) {
  30.                 final XmlResourceParser rp = loadXmlResourceParser(
  31.                         file, id, value.assetCookie, "drawable");
  32.                 dr = Drawable.createFromXml(wrapper, rp, theme);
  33.                 rp.close();
  34.             } else {
  35.                 final InputStream is = mAssets.openNonAsset(
  36.                         value.assetCookie, file, AssetManager.ACCESS_STREAMING);
  37.                 dr = Drawable.createFromResourceStream(wrapper, value, is, file, null);
  38.                 is.close();
  39.             }
  40.         } catch (Exception e) {
  41.             Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
  42.             final NotFoundException rnf = new NotFoundException(
  43.                     "File " + file + " from drawable resource ID #0x" + Integer.toHexString(id));
  44.             rnf.initCause(e);
  45.             throw rnf;
  46.         }
  47.         Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
  49.         return dr;
  50.     }

不从缓存获取的情况下，也就是首次获取走的是全新的解析流程

DrawableInflater.javaDrawable解析

  1. public Drawable inflateFromXml(@NonNull String name, @NonNull XmlPullParser parser, @NonNull AttributeSet attrs, @Nullable Theme theme)
  2.             throws XmlPullParserException, IOException {
  3.         // Inner classes must be referenced as Outer$Inner, but XML tag names
  4.         // can't contain $, so the <drawable> tag allows developers to specify
  5.         // the class in an attribute. We'll still run it through inflateFromTag
  6.         // to stay consistent with how LayoutInflater works.
  7.         // 解析自定义Drawable
  8.         if (name.equals("drawable")) {
  9.             name = attrs.getAttributeValue(null, "class");
  10.             if (name == null) {
  11.                 throw new InflateException("<drawable> tag must specify class attribute");
  12.             }
  13.         }
  15.         // 解析系统定义的drawable类
  16.         Drawable drawable = inflateFromTag(name);
  17.         if (drawable == null) {
  18.             // 没有则解析自定义的Drawable
  19.             drawable = inflateFromClass(name);
  20.         }
  21.         // inflate具体子类的实现，解析Drawable其他的属性
  22.         drawable.inflate(mRes, parser, attrs, theme);
  23.         return drawable;
  24.     }
  26. // 这里解析的对应系统的各类Drawable
  27. private Drawable inflateFromTag(@NonNull String name) {
  28.     switch (name) {
  29.         case "selector":
  30.             return new StateListDrawable();
  31.         case "animated-selector":
  32.             return new AnimatedStateListDrawable();
  33.         case "level-list":
  34.             return new LevelListDrawable();
  35.         case "layer-list":
  36.             return new LayerDrawable();
  37.         case "transition":
  38.             return new TransitionDrawable();
  39.         case "ripple":
  40.             return new RippleDrawable();
  41.         case "color":
  42.             return new ColorDrawable();
  43.         case "shape":
  44.             return new GradientDrawable();
  45.         case "vector":
  46.             return new VectorDrawable();
  47.         case "animated-vector":
  48.             return new AnimatedVectorDrawable();
  49.         case "scale":
  50.             return new ScaleDrawable();
  51.         case "clip":
  52.             return new ClipDrawable();
  53.         case "rotate":
  54.             return new RotateDrawable();
  55.         case "animated-rotate":
  56.             return new AnimatedRotateDrawable();
  57.         case "animation-list":
  58.             return new AnimationDrawable();
  59.         case "inset":
  60.             return new InsetDrawable();
  61.         case "bitmap":
  62.             return new BitmapDrawable();
  63.         case "nine-patch":
  64.             return new NinePatchDrawable();
  65.         default:
  66.             return null;
  67.     }
  68. }
  70. // 这里解析的是自定义的Drawable类，自API24+以后可以在xml文件中使用自定义的Drawable类
  71. private Drawable inflateFromClass(@NonNull String className) {
  72.     try {
  73.         Constructor<? extends Drawable> constructor;
  74.         synchronized (CONSTRUCTOR_MAP) {
  75.             constructor = CONSTRUCTOR_MAP.get(className);
  76.             if (constructor == null) {
  77.                 final Class<? extends Drawable> clazz =
  78. mClassLoader.loadClass(className).asSubclass(Drawable.class);
  79.                constructor = clazz.getConstructor();
  80.                CONSTRUCTOR_MAP.put(className, constructor);
  81.            }
  82.        }
  83.        return constructor.newInstance();
  84.    } catch (NoSuchMethodException e) {
  85.        final InflateException ie = new InflateException(
  86.                "Error inflating class " + className);
  87.        ie.initCause(e);
  88.        throw ie;
  89.    } catch (ClassCastException e) {
  90.        // If loaded class is not a Drawable subclass.
  91.        final InflateException ie = new InflateException(
  92.                "Class is not a Drawable " + className);
  93.        ie.initCause(e);
  94.        throw ie;
  95.    } catch (ClassNotFoundException e) {
  96.        // If loadClass fails, we should propagate the exception.
  97.        final InflateException ie = new InflateException(
  98.                "Class not found " + className);
  99.        ie.initCause(e);
  100.        throw ie;
  101.    } catch (Exception e) {
  102.        final InflateException ie = new InflateException(
  103.                "Error inflating class " + className);
  104.        ie.initCause(e);
  105.        throw ie;
  106.    }
  107. }
  1. 如果是系统自带的那些Drawable类，直接new出一个Drawable对象，到后面调用inflate将解析具体的每个实现类。
  2. 如果是我们自定义的Drawable，则用Class加载然后newInstancec出来，后面也可以通过inflate去解析其他的属性。
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