首先扯点别的：上海天气真的是太热了。
Resource 获取颜色
我们使用的颜色通常有两种，一种是在 src/main/res/values/colors.xml 文件中定义的普通的16进制的颜色。
<color name="colorPrimary">#FF3F51B5</color>
<color name="colorPrimaryDark">#303F9F</color>
<color name="colorAccent">#FFFF4081</color>
一种是在 src/main/res/color 目录下定义的xml格式的颜色文件。这种颜色是一个selector对象。例如: color_list.xml
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:color="#FF4081"/>
<item android:color="@color/colorPrimary" android:state_focused="true"/>
<item android:color="@color/colorPrimaryDark" android:state_pressed="true"/>
</selector>
加载颜色，调用 Resources 的 getColor() 方法。
public int getColor(@ColorRes int id, @Nullable Theme theme) throws NotFoundException {
final TypedValue value = obtainTempTypedValue();
try {
final ResourcesImpl impl = mResourcesImpl;
impl.getValue(id, value, true);
//注释1处，获取正常的16进制颜色
if (value.type >= TypedValue.TYPE_FIRST_iNT
&& value.type <= TypedValue.TYPE_LAST_iNT) {
//返回颜色
return value.data;
} else if (value.type != TypedValue.TYPE_STRING) {
throw new NotFoundException("Resource ID #0x" + Integer.toHexString(id)
+ " type #0x" + Integer.toHexString(value.type) + " is not valid");
}
//注释2处，获取在src/main/res/color 目录下定义的xml格式的颜色
final ColorStateList csl = impl.loadColorStateList(this, value, id, theme);
return csl.getDefaultColor();
}
finally {
releaseTempTypedValue(value);
}
}
注释1处，获取正常的16进制颜色并返回。
注释2处，获取在src/main/res/color 目录下定义的xml格式的颜色。调用 ResourcesImpl 的 loadColorStateList 方法。
@NonNull
ColorStateList loadColorStateList(Resources wrapper, TypedValue value, int id, Resources.Theme theme)
throws NotFoundException {
if (TRACE_FOR_PRELOAD) {
// Log only framework resources
if ((id >>> 24) == 0x1) {
final String name = getResourceName(id);
if (name != null) android.util.Log.d("PreloadColorStateList", name);
}
}
final long key = (((long) value.assetCookie) << 32) | value.data;
// Handle inline color definitions.
if (value.type >= TypedValue.TYPE_FIRST_COLOR_INT && value.type <= TypedValue.TYPE_LAST_COLOR_INT) {
return getColorStateListFromInt(value, key);
}
//注释1处，调用 loadComplexColorFromName 方法。
ComplexColor complexColor = loadComplexColorFromName(wrapper, theme, value, id);
if (complexColor != null && complexColor instanceof ColorStateList) {
//注释2处，返回获取的颜色值。
return (ColorStateList) complexColor;
}
throw new NotFoundException("Can't find ColorStateList from drawable resource ID #0x" + Integer.toHexString(id));
}
注释1处，调用 loadComplexColorFromName 方法。
@Nullable
private ComplexColor loadComplexColorFromName(Resources wrapper, Resources.Theme theme, TypedValue value, int id) {
final long key = (((long) value.assetCookie) << 32) | value.data;
final ConfigurationBoundResourceCache < ComplexColor > cache = mComplexColorCache;
ComplexColor complexColor = cache.getInstance(key, wrapper, theme);
//先从缓存里获取。
if (complexColor != null) {
return complexColor;
}
final android.content.res.ConstantState < ComplexColor > factory = sPreloadedComplexColors.get(key);
if (factory != null) {
complexColor = factory.newInstance(wrapper, theme);
}
if (complexColor == null) {
//注释1处，调用 loadComplexColorForCookie 方法。
complexColor = loadComplexColorForCookie(wrapper, value, id, theme);
}
if (complexColor != null) {
complexColor.setBaseChangingConfigurations(value.changingConfigurations);
if (mPreloading) {
if (verifyPreloadConfig(complexColor.getChangingConfigurations(), 0, value.resourceId, "color")) {
sPreloadedComplexColors.put(key, complexColor.getConstantState());
}
} else {
//注释2处，加入缓存
cache.put(key, theme, complexColor.getConstantState());
}
}
return complexColor;
}
注释1处，调用 loadComplexColorForCookie 方法。
@NonNull
private ComplexColor loadComplexColorForCookie(Resources wrapper, TypedValue value, int id, Resources.Theme theme) {
if(value.string == null) {
throw new UnsupportedOperationException("Can't convert to ComplexColor: type=0x" + value.type);
}
//注释1处，在这个例子中就是 res/color/color_list.xml
final String file = value.string.toString();
if(TRACE_FOR_MISS_PRELOAD) {
// Log only framework resources
if((id >>> 24) == 0x1) {
final String name = getResourceName(id);
if(name != null) {
Log.d(TAG, "Loading framework ComplexColor #" + Integer.toHexString(id) + ": " + name + " at " + file);
}
}
}
if(DEBUG_LOAD) {
Log.v(TAG, "Loading ComplexColor for cookie " + value.assetCookie + ": " + file);
}
ComplexColor complexColor = null;
Trace.traceBegin(Trace.TRACE_TAG_RESOURCES, file);
//注释2处，在res/color/文件夹下定义的颜色必须是以xml文件
if(file.endsWith(".xml")) {
try {
final XmlResourceParser parser = loadXmlResourceParser(file, id, value.assetCookie, "ComplexColor");
final AttributeSet attrs = Xml.asAttributeSet(parser);
int type;
while((type = parser.next()) != XmlPullParser.START_TAG && type != XmlPullParser.END_DOCUMENT) {
// Seek parser to start tag.
}
if(type != XmlPullParser.START_TAG) {
throw new XmlPullParserException("No start tag found");
}
final String name = parser.getName();
//注释3处，处理渐变色类型
if(name.equals("gradient")) {
complexColor = GradientColor.createFromXmlInner(wrapper, parser, attrs, theme);
} else if(name.equals("selector")) {
//注释4处，处理selector类型
complexColor = ColorStateList.createFromXmlInner(wrapper, parser, attrs, theme);
}
parser.close();
} catch(Exception e) {
Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
final NotFoundException rnf = new NotFoundException("File " + file + " from ComplexColor resource ID #0x" + Integer.toHexString(id));
rnf.initCause(e);
throw rnf;
}
} else {
Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
throw new NotFoundException("File " + file + " from drawable resource ID #0x" + Integer.toHexString(id) + ": .xml extension required");
}
Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
return complexColor;
}
注释1处，在这个例子中就是 res/color/color_list.xml。
注释2处，在res/color/文件夹下定义的颜色必须是以xml文件。
注释3处，处理渐变色类型。
注释4处，处理selector类型。
回到 loadComplexColorFromName 方法的 注释2处，将获取到的颜色加入缓存，下次就不用再次解析xml文件了。
回到 ResourcesImpl 的 loadColorStateList 方法的注释2处，返回获取的颜色值。
回到 Resources 的 getColor() 方法的注释2处，获取在src/main/res/color 目录下定义的xml格式的颜色，并且返回的是xml文件中默认状态的颜色。在这个例子中就是selector文件中的
<item android:color="#FF4081"/> 。
Resource获取图片
Resource 的 getDrawable 方法。
public Drawable getDrawable(@DrawableRes int id, @Nullable Theme theme)
throws NotFoundException {
return getDrawableForDensity(id, 0, theme);
}
Resources 的 getDrawableForDensity 方法。
public Drawable getDrawableForDensity(@DrawableRes int id, int density, @Nullable Theme theme) {
final TypedValue value = obtainTempTypedValue();
try {
final ResourcesImpl impl = mResourcesImpl;
//注释1处，调用ResourcesImpl 的 getValueForDensity 方法。
impl.getValueForDensity(id, density, value, true);
//注释2处，调用ResourcesImpl 的loadDrawable 方法。
return impl.loadDrawable(this, value, id, density, theme);
}
finally {
releaseTempTypedValue(value);
}
}
注释1处，调用ResourcesImpl 的 getValueForDensity 方法。
void getValueForDensity(@AnyRes int id, int density, TypedValue outValue,
Boolean resolveRefs) throws NotFoundException {
//注释1处，调用 AssetManager 的 getResourceValue 方法。
Boolean found = mAssets.getResourceValue(id, density, outValue, resolveRefs);
if (found) {
return;
}
throw new NotFoundException("Resource ID #0x" + Integer.toHexString(id));
}
注释1处，调用 AssetManager 的 getResourceValue 方法。这个方法大概就是返回资源在特定密度下的信息，返回的信息存储在 outValue 中，如果传入的 densityDpi 参数为0 ，就使用当前 Configuration 中的density。
final Boolean getResourceValue(@AnyRes int resId, int densityDpi, @NonNull TypedValue outValue,
Boolean resolveRefs) {
synchronized (this) {
//注释1处，调用 loadResourceValue 方法。 这是一个 native方法。
final int block = loadResourceValue(resId, (short) densityDpi, outValue, resolveRefs);
if (block < 0) {
return false;
}
// Convert the changing configurations flags populated by native code.
outValue.changingConfigurations = ActivityInfo.activityInfoConfigNativeToJava(
outValue.changingConfigurations);
if (outValue.type == TypedValue.TYPE_STRING) {
outValue.string = mStringBlocks[block].get(outValue.data);
}
return true;
}
}
Resources 的 getDrawableForDensity 方法的注释2处 ，调用ResourcesImpl 的loadDrawable 方法。
Drawable loadDrawable(@NonNull Resources wrapper, @NonNull TypedValue value, int id,
int density, @Nullable Resources.Theme theme)
throws NotFoundException {
// If the drawable's XML lives in our current density qualifier,
// it's okay to use a scaled version from the cache. Otherwise, we
// need to actually load the drawable from XML.
//注释0处，在密度为0，或者传入的密度和当前的密度一样的时候，使用缓存。
final Boolean useCache = density == 0 || value.density == mMetrics.densityDpi;
// Pretend the requested density is actually the display density. If
// the drawable returned is not the requested density, then force it
// to be scaled later by dividing its density by the ratio of
// requested density to actual device density. Drawables that have
// undefined density or no density don't need to be handled here.
if (density > 0 && value.density > 0 && value.density != TypedValue.DENSITY_NONE) {
if (value.density == density) {
value.density = mMetrics.densityDpi;
} else {
value.density = (value.density * mMetrics.densityDpi) / density;
}
}
try {
//...
//标记是否是 ColorDrawable
final Boolean isColorDrawable;
//该主题下的绘制资源缓存
final DrawableCache caches;
final long key;
//注释1处，条件满足则代表是 ColorDrawable ，我的理解 ColorDrawable 就是我们直接给 View 的 Background 设置一个颜色。 例如 android:background="@color/colorPrimary"
if (value.type >= TypedValue.TYPE_FIRST_COLOR_iNT
&& value.type <= TypedValue.TYPE_LAST_COLOR_iNT) {
isColorDrawable = true;
caches = mColorDrawableCache;
key = value.data;
} else {
isColorDrawable = false;
caches = mDrawableCache;
key = (((long) value.assetCookie) << 32) | value.data;
}
// First, check whether we have a cached version of this drawable
// that was inflated against the specified theme. Skip the cache if
// we're currently preloading or we're not using the cache.
if (!mPreloading && useCache) {
//条件为true
final Drawable cachedDrawable = caches.getInstance(key, wrapper, theme);
if (cachedDrawable != null) {
//注释2处，从缓存中获取的不为null，直接返回。
cachedDrawable.setChangingConfigurations(value.changingConfigurations);
return cachedDrawable;
}
}
// Next, check preloaded drawables. Preloaded drawables may contain
// unresolved theme attributes.
//注释3处，从预加载的资源中获取，只有 zygote 进程才会预加载一些资源，这些资源是共享的。系统中的每个应用都可以使用。
final Drawable.ConstantState cs;
if (isColorDrawable) {
cs = sPreloadedColorDrawables.get(key);
} else {
cs = sPreloadedDrawables[mConfiguration.getLayoutDirection()].get(key);
}
Drawable dr;
Boolean needsNewDrawableAfterCache = false;
if (cs != null) {
if (TRACE_FOR_DETAILED_PRELOAD) {
// Log only framework resources
if (((id >>> 24) == 0x1) && (android.os.Process.myUid() != 0)) {
final String name = getResourceName(id);
//命中的预加载的资源
if (name != null) {
Log.d(TAG_PRELOAD, "Hit preloaded FW drawable #"
+ Integer.toHexString(id) + " " + name);
}
}
}
//注释4处，从预加载的资源中获取Drawable
dr = cs.newDrawable(wrapper);
} else if (isColorDrawable) {
//注释5处，创建新的 ColorDrawable
dr = new ColorDrawable(value.data);
} else {
//注释6处，创建新的 Drawable 从 XML文件或者 资源流中加载 drawable
dr = loadDrawableForCookie(wrapper, value, id, density);
}
// DrawableContainer' constant state has drawables instances. In order to leave the
// constant state intact in the cache, we need to create a new DrawableContainer after
// added to cache.
if (dr instanceof DrawableContainer) {
needsNewDrawableAfterCache = true;
}
// Determine if the drawable has unresolved theme attributes. If it
// does, we'll need to apply a theme and store it in a theme-specific
// cache.
//应用主题
final Boolean canApplyTheme = dr != null && dr.canApplyTheme();
if (canApplyTheme && theme != null) {
dr = dr.mutate();
dr.applyTheme(theme);
dr.clearMutated();
}
// 如果我们能够获取一个 drawable，把它加入合适的缓存：预加载的缓存，没有主题的缓存，null主题的缓存，特定主题的缓存。
if (dr != null) {
dr.setChangingConfigurations(value.changingConfigurations);
if (useCache) {
//加入缓存
cacheDrawable(value, isColorDrawable, caches, theme, canApplyTheme, key, dr);
if (needsNewDrawableAfterCache) {
Drawable.ConstantState state = dr.getConstantState();
if (state != null) {
dr = state.newDrawable(wrapper);
}
}
}
}
return dr;
}
catch (Exception e) {
String name;
try {
name = getResourceName(id);
}
catch (NotFoundException e2) {
name = "(missing name)";
}
// The target drawable might fail to load for any number of
// reasons, but we always want to include the resource name.
// Since the client already expects this method to throw a
// NotFoundException, just throw one of those.
final NotFoundException nfe = new NotFoundException("Drawable " + name
+ " with resource ID #0x" + Integer.toHexString(id), e);
nfe.setStackTrace(new StackTraceElement[0]);
throw nfe;
}
}
注释0处，在密度为0，或者传入的密度和当前的密度一样的时候，使用缓存。
注释1处，条件满足则代表是 ColorDrawable ，我的理解 ColorDrawable 就是我们直接给 View 的 Background 设置一个颜色。 例如 android:background=“@color/colorPrimary” 。
注释2处，从缓存中获取的不为null，直接返回。
注释3处，从预加载的资源中获取，只有 zygote 进程才会预加载一些资源，这些资源是共享的。系统中的每个应用都可以使用。
注释4处，如果是预加载的资源，就使用预加载的资源获取Drawable。
注释5处，创建新的 ColorDrawable。
注释6处，创建新的 Drawable 从 XML文件或者 资源流中加载 drawable。
注释6处，创建新的 Drawable
/**
* 从 XML文件或者 资源流中加载 drawable
*
* @return Drawable, or null if Drawable cannot be decoded.
*/
@Nullable
private Drawable loadDrawableForCookie(@NonNull Resources wrapper, @NonNull TypedValue value, int id, int density) {
if(value.string == null) {
throw new NotFoundException("Resource "
" + getResourceName(id) + "
" (" + Integer.toHexString(id) + ") is not a Drawable (color or path): " + value);
}
//注释0处， 类似 res/drawable-xxhdpi-v4/avatar.png
final String file = value.string.toString();
if(TRACE_FOR_MISS_PRELOAD) {
// Log only framework resources
if((id >>> 24) == 0x1) {
final String name = getResourceName(id);
if(name != null) {
Log.d(TAG, "Loading framework drawable #" + Integer.toHexString(id) + ": " + name + " at " + file);
}
}
}
// For preload tracing.
long startTime = 0;
int startBitmapCount = 0;
long startBitmapSize = 0;
int startDrawableCount = 0;
if(TRACE_FOR_DETAILED_PRELOAD) {
startTime = System.nanoTime();
startBitmapCount = Bitmap.sPreloadTracingNumInstantiatedBitmaps;
startBitmapSize = Bitmap.sPreloadTracingTotalBitmapsSize;
startDrawableCount = sPreloadTracingNumLoadedDrawables;
}
if(DEBUG_LOAD) {
Log.v(TAG, "Loading drawable for cookie " + value.assetCookie + ": " + file);
}
final Drawable dr;
Trace.traceBegin(Trace.TRACE_TAG_RESOURCES, file);
LookupStack stack = mLookupStack.get();
try {
// Perform a linear search to check if we have already referenced this resource before.
if(stack.contains(id)) {
throw new Exception("Recursive reference in drawable");
}
stack.push(id);
try {
//注释1处，从 xml 文件加载
if(file.endsWith(".xml")) {
final XmlResourceParser rp = loadXmlResourceParser(file, id, value.assetCookie, "drawable");
dr = Drawable.createFromXmlForDensity(wrapper, rp, density, null);
rp.close();
} else {
//注释2处，加载 .png，.jpg 等
final InputStream is = mAssets.openNonAsset(value.assetCookie, file, AssetManager.ACCESS_STREAMING);
AssetInputStream ais = (AssetInputStream) is;
dr = decodeImageDrawable(ais, wrapper, value);
}
} finally {
stack.pop();
}
} catch(Exception | StackOverflowError e) {
Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
final NotFoundException rnf = new NotFoundException("File " + file + " from drawable resource ID #0x" + Integer.toHexString(id));
rnf.initCause(e);
throw rnf;
}
Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
if(TRACE_FOR_DETAILED_PRELOAD) {
if(((id >>> 24) == 0x1)) {
final String name = getResourceName(id);
if(name != null) {
final long time = System.nanoTime() - startTime;
final int loadedBitmapCount = Bitmap.sPreloadTracingNumInstantiatedBitmaps - startBitmapCount;
final long loadedBitmapSize = Bitmap.sPreloadTracingTotalBitmapsSize - startBitmapSize;
final int loadedDrawables = sPreloadTracingNumLoadedDrawables - startDrawableCount;
sPreloadTracingNumLoadedDrawables++;
final Boolean isRoot = (android.os.Process.myUid() == 0);
Log.d(TAG_PRELOAD, (isRoot ? "Preloaded FW drawable #" : "Loaded non-preloaded FW drawable #") + Integer.toHexString(id) + " " + name + " " + file + " " + dr.getClass().getCanonicalName() + " #nested_drawables= " + loadedDrawables + " #bitmaps= " + loadedBitmapCount + " total_bitmap_size= " + loadedBitmapSize + " in[us] " + (time / 1000));
}
}
}
return dr;
}
注释0处， 类似 res/drawable-xxhdpi-v4/avatar.png 代表是png文件，如果是xml类型的drawable，则类似 res/drawable/avatar_two.xml 。
注释1处，从 xml 文件加载。
注释2处，加载 .png，.jpg 等格式的文件。
总结：整体看下来大致流程还是比较简单。