一、加载layout 布局文件的逻辑：
image-20210630133727716.png
1、初始化窗口及根布局：
1.1）从activity加载布局文件的过程分析，并来收集每一个view的属性名和value，ActivityThread 类中的performLaunchActivity()方法来启动activity
首先创建Activity
ContextImpl appContext = createBaseContextForActivity(r);
Activity activity = null;
java.lang.ClassLoader cl = appContext.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
1.2) 调用activity的attach()方法
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.referrer, r.voiceInteractor, window, r.configCallback,
r.assistToken);
1.3) 进入Activity 类 找到attach()方法 他会创建一个phoneWindow的对象
mWindow = new PhoneWindow(this, window, activityConfigCallback);
14) 创建后phoneWindow后，我们来看activity的setContentView()方法：
public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
1.5) 这里就是调用的上一步创建好的phoneWindow的setContentView()方法：
public void setContentView(int layoutResID) {
if (mContentParent == null) {
installDecor();
} else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
mContentParent.removeAllViews();
}
if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
getContext());
transitionTo(newScene);
} else {
mLayoutInflater.inflate(layoutResID, mContentParent);
}
}
1.6) 继续进入到：installDecor(); 先生成一个 DecorView mDecor;而这个DecorView 其实就是一个FrameLayout
mDecor = generateDecor(-1);
//然后将这个mDecor作为根传递到generateLayout方法中，
ViewGroup mContentParent = generateLayout(mDecor);
1.7) 这里会生成一个布局进入：generateLayout(mDecor);然后找到系统资源文件中的布局id,并生成根视图返回
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
截止到现在，我们已经知道activity的窗口已经已经好了，而且在窗口给我们添加了一个默认的布局frameLayout.这些工作都是系统在帮我们做，加下来看看如何加载我们自己定义的布局。
2、加载自定义的布局文件setContentView()
找到了mContentParent的创建的地方后，我们继续回到PhoneWindow类的setContentView()中
image-20210630134116133.png
2.1）mLayoutInflater.inflate(layoutResID, mContentParent);
说明：
1）这里把我们上一步创建好的mContentParent传递进去，
2）layoutResID 就是我们在自己的activity中的布局文件ID
3）一个参数attachToRoot的作用： true代码动态加载 false 代表将我们自己的根布局的参数添加的DecorView中去
public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
// Temp is the root view that was found in the xml
final View temp = createViewFromTag(root, name, inflaterContext, attrs);
// Create layout params that match root, if supplied
params = root.generateLayoutParams(attrs);
if (!attachToRoot) {
// Set the layout params for temp if we are not
// attaching. (If we are, we use addView, below)
temp.setLayoutParams(params);
}
}
2.2）继续进createViewFromTag()方法中去
说明：
1) 此处就是LayoutInflater 帮助我们创建自定义View的核心代码区域，两种方式来创建：一种是Factory的方式 ；一种是infalter的createView()反射方式
View view = tryCreateView(parent, name, context, attrs);
if (view == null) {
final Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = context;
try {
if (-1 == name.indexOf('.')) {
view = onCreateView(context, parent, name, attrs);
} else {
view = createView(context, name, null, attrs);
}
} finally {
mConstructorArgs[0] = lastContext;
}
}
2.3）我们先进入tryCreateView()方法看看
特别强调：
在中间View的创建是通过Factory工程模式来进行创建的，而Factory是给我们定义的一个接口，由此可见我们也可以来通过自定义这个Factory的方式来实现工厂的onCreatView()方法，方法中抄袭系统的createView()的实现来完成视图View的创建。
public final View tryCreateView(@Nullable View parent, @NonNull String name,
@NonNull Context context,
@NonNull AttributeSet attrs) {
if (name.equals(TAG_1995)) {
// Let's party like it's 1995!
return new BlinkLayout(context, attrs);
}
View view;
if (mFactory2 != null) {
view = mFactory2.onCreateView(parent, name, context, attrs);
} else if (mFactory != null) {
view = mFactory.onCreateView(name, context, attrs);
} else {
view = null;
}
if (view == null && mPrivateFactory != null) {
view = mPrivateFactory.onCreateView(parent, name, context, attrs);
}
return view;
}
2.4）View的创建都是通过调用LayoutInflater.java中的creatView（）方法来完成的
public final View createView(@NonNull Context viewContext, @NonNull String name,
@Nullable String prefix, @Nullable AttributeSet attrs)
throws ClassNotFoundException, InflateException {
Objects.requireNonNull(viewContext);
Objects.requireNonNull(name);
Constructor<? extends View> constructor = sConstructorMap.get(name);
if (constructor != null && !verifyClassLoader(constructor)) {
constructor = null;
sConstructorMap.remove(name);
}
Class<? extends View> clazz = null;
try {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, name);
if (constructor == null) {
// Class not found in the cache, see if it's real, and try to add it
clazz = Class.forName(prefix != null ? (prefix + name) : name, false,
mContext.getClassLoader()).asSubclass(View.class);
if (mFilter != null && clazz != null) {
boolean allowed = mFilter.onLoadClass(clazz);
if (!allowed) {
failNotAllowed(name, prefix, viewContext, attrs);
}
}
constructor = clazz.getConstructor(mConstructorSignature);//此处可以说明所有的自定义都会调用两个参数的构造函数
constructor.setAccessible(true);
sConstructorMap.put(name, constructor);
} else {
// If we have a filter, apply it to cached constructor
if (mFilter != null) {
// Have we seen this name before?
Boolean allowedState = mFilterMap.get(name);
if (allowedState == null) {
// New class -- remember whether it is allowed
clazz = Class.forName(prefix != null ? (prefix + name) : name, false,
mContext.getClassLoader()).asSubclass(View.class);
boolean allowed = clazz != null && mFilter.onLoadClass(clazz);
mFilterMap.put(name, allowed);
if (!allowed) {
failNotAllowed(name, prefix, viewContext, attrs);
}
} else if (allowedState.equals(Boolean.FALSE)) {
failNotAllowed(name, prefix, viewContext, attrs);
}
}
}
Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = viewContext;
Object[] args = mConstructorArgs;
args[1] = attrs;
try {
//此处就创建好了我们自己定义的layoutView
final View view = constructor.newInstance(args);
if (view instanceof ViewStub) {
// Use the same context when inflating ViewStub later.
final ViewStub viewStub = (ViewStub) view;
viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
}
return view;
} finally {
mConstructorArgs[0] = lastContext;
}
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}
通过上述createView我们可以发现，自定义的view是通过反射来进行加载的，最后将通过反射创建出一个view的实例并返回回去
3、加载资源文件(ActivityThread.java 中的handleBindApplication(AppBindData data)方法中开始)
3.1) 创建一个仪表类
mInstrumentation = new Instrumentation();
3.2) 创建application
app = data.info.makeApplication(data.restrictedBackupMode, null);
3.2.1 )进入makeApplication()中，LoadedApk.java中的makeApplication方法中去，进行上下文创建：
ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);
3.2.2) 创建上下文的方法
static ContextImpl createAppContext(ActivityThread mainThread, LoadedApk packageInfo,
String opPackageName) {
if (packageInfo == null) throw new IllegalArgumentException("packageInfo");
ContextImpl context = new ContextImpl(null, mainThread, packageInfo, null, null, null, null,
0, null, opPackageName);
context.setResources(packageInfo.getResources());
context.mIsSystemOrSystemUiContext = isSystemOrSystemUI(context);
return context;
}
3.2.3) 在创建上下文是需要配置context.setResources()设置资源信息，此时传入的packageInfo.getResources()
public Resources getResources() {
if (mResources == null) {
final String[] splitPaths;
try {
splitPaths = getSplitPaths(null);
} catch (NameNotFoundException e) {
// This should never fail.
throw new AssertionError("null split not found");
}
mResources = ResourcesManager.getInstance().getResources(null, mResDir,
splitPaths, mOverlayDirs, mApplicationInfo.sharedLibraryFiles,
Display.DEFAULT_DISPLAY, null, getCompatibilityInfo(),
getClassLoader(), null);
}
return mResources;
}
3.2.4) 接着进入 ResourcesManager.getInstance()的getResources()方法中去
public @Nullable Resources getResources() {
try {
Trace.traceBegin(Trace.TRACE_TAG_RESOURCES, "ResourcesManager#getResources");
final ResourcesKey key = new ResourcesKey(
resDir,
splitResDirs,
overlayDirs,
libDirs,
displayId,
overrideConfig != null ? new Configuration(overrideConfig) : null, // Copy
compatInfo,
loaders == null ? null : loaders.toArray(new ResourcesLoader[0]));
classLoader = classLoader != null ? classLoader : ClassLoader.getSystemClassLoader();
if (activityToken != null) {
rebaseKeyForActivity(activityToken, key);
}
return createResources(activityToken, key, classLoader);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);
}
}
3.2.5) 接着进入createResources(),然后再进入findOrCreateResourcesImplForKeyLocked中去
private @Nullable Resources createResources(@Nullable IBinder activityToken,
@NonNull ResourcesKey key, @NonNull ClassLoader classLoader) {
synchronized (this) {
if (DEBUG) {
Throwable here = new Throwable();
here.fillInStackTrace();
Slog.w(TAG, "!! Get resources for activity=" + activityToken + " key=" + key, here);
}
ResourcesImpl resourcesImpl = findOrCreateResourcesImplForKeyLocked(key);
if (resourcesImpl == null) {
return null;
}
if (activityToken != null) {
return createResourcesForActivityLocked(activityToken, classLoader,
resourcesImpl, key.mCompatInfo);
} else {
return createResourcesLocked(classLoader, resourcesImpl, key.mCompatInfo);
}
}
}
private @Nullable ResourcesImpl findOrCreateResourcesImplForKeyLocked(
@NonNull ResourcesKey key) {
ResourcesImpl impl = findResourcesImplForKeyLocked(key);
if (impl == null) {
impl = createResourcesImpl(key);
if (impl != null) {
mResourceImpls.put(key, new WeakReference<>(impl));
}
}
return impl;
}
3.2.6) 接着看看ResourcesImpl的实现：
private @Nullable ResourcesImpl createResourcesImpl();
final AssetManager assets = createAssetManager(key);
if (assets == null) {
return null;
}
final DisplayMetrics dm = getDisplayMetrics(key.mDisplayId, daj);
final Configuration config = generateConfig(key, dm);
final ResourcesImpl impl = new ResourcesImpl(assets, dm, config, daj);
if (DEBUG) {
Slog.d(TAG, "- creating impl=" + impl + " with key: " + key);
}
return impl;
}
3.2.7) 进入createAssetManager()方法,创建好了AssetManager的对象后返回该对象，用于生成ResourcesImpl 构建对象，这样就可以得到我们apk包中的资源了
protected @Nullable AssetManager createAssetManager(@NonNull final ResourcesKey key) {
final AssetManager.Builder builder = new AssetManager.Builder();
// resDir can be null if the 'android' package is creating a new Resources object.
// This is fine, since each AssetManager automatically loads the 'android' package
// already.
if (key.mResDir != null) {
try {
builder.addApkAssets(loadApkAssets(key.mResDir, false /*sharedLib*/,
false /*overlay*/));
} catch (IOException e) {
Log.e(TAG, "failed to add asset path " + key.mResDir);
return null;
}
}
if (key.mSplitResDirs != null) {
for (final String splitResDir : key.mSplitResDirs) {
try {
builder.addApkAssets(loadApkAssets(splitResDir, false /*sharedLib*/,
false /*overlay*/));
} catch (IOException e) {
Log.e(TAG, "failed to add split asset path " + splitResDir);
return null;
}
}
}
if (key.mLibDirs != null) {
for (final String libDir : key.mLibDirs) {
if (libDir.endsWith(".apk")) {
// Avoid opening files we know do not have resources,
// like code-only .jar files.
try {
builder.addApkAssets(loadApkAssets(libDir, true /*sharedLib*/,
false /*overlay*/));
} catch (IOException e) {
Log.w(TAG, "Asset path '" + libDir +
"' does not exist or contains no resources.");
// continue.
}
}
}
}
if (key.mOverlayDirs != null) {
for (final String idmapPath : key.mOverlayDirs) {
try {
builder.addApkAssets(loadApkAssets(idmapPath, false /*sharedLib*/,
true /*overlay*/));
} catch (IOException e) {
Log.w(TAG, "failed to add overlay path " + idmapPath);
// continue.
}
}
}
if (key.mLoaders != null) {
for (final ResourcesLoader loader : key.mLoaders) {
builder.addLoader(loader);
}
}
return builder.build();
}
到目前为止，我们已经找到了ResoucesImpl的实现,完成了上面的工作后，就会回调到我们自己app的application的OnCreate()方法中了。
mInstrumentation.callApplicationOnCreate(app);
二、使用加载好的资源
image-20210630142700047.png
2.1) resources.getDrawable()
public Drawable getDrawableForDensity(@DrawableRes int id, int density, @Nullable Theme theme) {
final TypedValue value = obtainTempTypedValue();
try {
final ResourcesImpl impl = mResourcesImpl;
impl.getValueForDensity(id, density, value, true);
return loadDrawable(value, id, density, theme);
} finally {
releaseTempTypedValue(value);
}
}
2.2) resources.getString()/resources.getText()
@NonNull public CharSequence getText(@StringRes int id) throws NotFoundException {
CharSequence res = mResourcesImpl.getAssets().getResourceText(id);
if (res != null) {
return res;
}
throw new NotFoundException("String resource ID #0x"
+ Integer.toHexString(id));
}
2.3) resources.getColor()
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);
if (value.type >= TypedValue.TYPE_FIRST_INT
&& value.type <= TypedValue.TYPE_LAST_INT) {
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");
}
final ColorStateList csl = impl.loadColorStateList(this, value, id, theme);
return csl.getDefaultColor();
} finally {
releaseTempTypedValue(value);
}
}
2.4)resources.getAnimation()
XmlResourceParser loadXmlResourceParser(@AnyRes int id, @NonNull String type)
throws NotFoundException {
final TypedValue value = obtainTempTypedValue();
try {
final ResourcesImpl impl = mResourcesImpl;
impl.getValue(id, value, true);
if (value.type == TypedValue.TYPE_STRING) {
return loadXmlResourceParser(value.string.toString(), id,
value.assetCookie, type);
}
throw new NotFoundException("Resource ID #0x" + Integer.toHexString(id)
+ " type #0x" + Integer.toHexString(value.type) + " is not valid");
} finally {
releaseTempTypedValue(value);
}
}
2.5)resources.getDimension()
public float getDimension(@DimenRes int id) throws NotFoundException {
final TypedValue value = obtainTempTypedValue();
try {
final ResourcesImpl impl = mResourcesImpl;
impl.getValue(id, value, true);
if (value.type == TypedValue.TYPE_DIMENSION) {
return TypedValue.complexToDimension(value.data, impl.getDisplayMetrics());
}
throw new NotFoundException("Resource ID #0x" + Integer.toHexString(id)
+ " type #0x" + Integer.toHexString(value.type) + " is not valid");
} finally {
releaseTempTypedValue(value);
}
}
从上面的代码我们可以看到，所有资源的获取都会最终调用到AssetManager的getResourceValue()方法中去
boolean getResourceValue(@AnyRes int resId, int densityDpi, @NonNull TypedValue outValue,
boolean resolveRefs) {
Objects.requireNonNull(outValue, "outValue");
synchronized (this) {
ensureValidLocked();
final int cookie = nativeGetResourceValue(
mObject, resId, (short) densityDpi, outValue, resolveRefs);
if (cookie <= 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 = getPooledStringForCookie(cookie, outValue.data);
}
return true;
}
}
完成上面的步骤后，接下来是回调回我们app的application的onCreate()方法中：
mInstrumentation.callApplicationOnCreate(app);
以上就是加载我们的布局和资源文件的全部过程已经相关方法的调用顺序。有了上面的基础，在实现换肤功能时，就有了初步思路了。（具体的换肤思路在后面的实战换肤文章中详说）。
