Android Resource类创建过程（未完）

这篇文章主要讲述Android一个应用里面Resource资源是怎么初始化的，要讲述这个题目首先要提到一个应用是怎么初始化的。

一、应用的初始化

一个应用的起始地方是在ActivityThread的main方法里面

    public static void main(String[] args) {
        SamplingProfilerIntegration.start();

        // CloseGuard defaults to true and can be quite spammy.  We
        // disable it here, but selectively enable it later (via
        // StrictMode) on debug builds, but using DropBox, not logs.
        CloseGuard.setEnabled(false);

        Environment.initForCurrentUser();

        // Set the reporter for event logging in libcore
        EventLogger.setReporter(new EventLoggingReporter());

        Security.addProvider(new AndroidKeyStoreProvider());

        Process.setArgV0("<pre-initialized>");

        Looper.prepareMainLooper();

        ActivityThread thread = new ActivityThread();
        thread.attach(false);

        if (sMainThreadHandler == null) {
            sMainThreadHandler = thread.getHandler();
        }

        AsyncTask.init();

        if (false) {
            Looper.myLooper().setMessageLogging(new
                    LogPrinter(Log.DEBUG, "ActivityThread"));
        }

        Looper.loop();

        throw new RuntimeException("Main thread loop unexpectedly exited");
    }

在这个方法内部创建了一个ActivityThread（主线程），并且完善了Handler和Looper，并且用成员H (extends Handler) 和AMS进行通信，AMS最终通过H来发送以下的message：

        public void handleMessage(Message msg) {
            if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
            switch (msg.what) {
                case LAUNCH_ACTIVITY: {
                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
                    ActivityClientRecord r = (ActivityClientRecord)msg.obj;

                    r.packageInfo = getPackageInfoNoCheck(
                            r.activityInfo.applicationInfo, r.compatInfo);
                    handleLaunchActivity(r, null);
                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                } break;

可以看到最终调用到ActivityThread的handleLaunchActivity方法，最终调用到performLaunchActivity这个方法里面，我们来瞧瞧这个方法吧。

ActivityThread.java:

    private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
        // System.out.println("##### [" + System.currentTimeMillis() + "] ActivityThread.performLaunchActivity(" + r + ")");

        ActivityInfo aInfo = r.activityInfo;
        if (r.packageInfo == null) {
            r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,
                    Context.CONTEXT_INCLUDE_CODE);
        }

        ComponentName component = r.intent.getComponent();
        if (component == null) {
            component = r.intent.resolveActivity(
                mInitialApplication.getPackageManager());
            r.intent.setComponent(component);
        }

        if (r.activityInfo.targetActivity != null) {
            component = new ComponentName(r.activityInfo.packageName,
                    r.activityInfo.targetActivity);
        }

        Activity activity = null;
        try {
            java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
            activity = mInstrumentation.newActivity(
                    cl, component.getClassName(), r.intent);
            StrictMode.incrementExpectedActivityCount(activity.getClass());
            r.intent.setExtrasClassLoader(cl);
            if (r.state != null) {
                r.state.setClassLoader(cl);
            }
        } catch (Exception e) {
            if (!mInstrumentation.onException(activity, e)) {
                throw new RuntimeException(
                    "Unable to instantiate activity " + component
                    + ": " + e.toString(), e);
            }
        }

        try {
            Application app = r.packageInfo.makeApplication(false, mInstrumentation);

            if (localLOGV) Slog.v(TAG, "Performing launch of " + r);
            if (localLOGV) Slog.v(
                    TAG, r + ": app=" + app
                    + ", appName=" + app.getPackageName()
                    + ", pkg=" + r.packageInfo.getPackageName()
                    + ", comp=" + r.intent.getComponent().toShortString()
                    + ", dir=" + r.packageInfo.getAppDir());

            if (activity != null) {
                Context appContext = createBaseContextForActivity(r, activity);
                CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
                Configuration config = new Configuration(mCompatConfiguration);
                if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "
                        + r.activityInfo.name + " with config " + config);
                activity.attach(appContext, this, getInstrumentation(), r.token,
                        r.ident, app, r.intent, r.activityInfo, title, r.parent,
                        r.embeddedID, r.lastNonConfigurationInstances, config);

                if (customIntent != null) {
                    activity.mIntent = customIntent;
                }
                r.lastNonConfigurationInstances = null;
                activity.mStartedActivity = false;
                int theme = r.activityInfo.getThemeResource();
                if (theme != 0) {
                    activity.setTheme(theme);
                }

                activity.mCalled = false;
                mInstrumentation.callActivityOnCreate(activity, r.state);
                if (!activity.mCalled) {
                    throw new SuperNotCalledException(
                        "Activity " + r.intent.getComponent().toShortString() +
                        " did not call through to super.onCreate()");
                }
                r.activity = activity;
                r.stopped = true;
                if (!r.activity.mFinished) {
                    activity.performStart();
                    r.stopped = false;
                }
                if (!r.activity.mFinished) {
                    if (r.state != null) {
                        mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
                    }
                }
                if (!r.activity.mFinished) {
                    activity.mCalled = false;
                    mInstrumentation.callActivityOnPostCreate(activity, r.state);
                    if (!activity.mCalled) {
                        throw new SuperNotCalledException(
                            "Activity " + r.intent.getComponent().toShortString() +
                            " did not call through to super.onPostCreate()");
                    }
                }
            }
            r.paused = true;

            mActivities.put(r.token, r);

        } catch (SuperNotCalledException e) {
            throw e;

        } catch (Exception e) {
            if (!mInstrumentation.onException(activity, e)) {
                throw new RuntimeException(
                    "Unable to start activity " + component
                    + ": " + e.toString(), e);
            }
        }

        return activity;
    }

这个函数完成了Activity的创建过程，一些Activity生命周期相关的调用也在这里出现了，比如上面代码里面的 mInstrumentation.callActivityOnCreate(activity, r.state);  这句话最终会调用到Activity的onCreate方法。但是因为这些和我们的主题并没有太大的关系，所以这里就略过了。

下面着重看这些

Context appContext = createBaseContextForActivity(r, activity);
                CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
                Configuration config = new Configuration(mCompatConfiguration);
                if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "
                        + r.activityInfo.name + " with config " + config);
                activity.attach(appContext, this, getInstrumentation(), r.token,
                        r.ident, app, r.intent, r.activityInfo, title, r.parent,
                        r.embeddedID, r.lastNonConfigurationInstances, config);

...
    private Context createBaseContextForActivity(ActivityClientRecord r,
            final Activity activity) {
        ContextImpl appContext = new ContextImpl();
        appContext.init(r.packageInfo, r.token, this);
        appContext.setOuterContext(activity);

        // For debugging purposes, if the activity's package name contains the value of
        // the "debug.use-second-display" system property as a substring, then show
        // its content on a secondary display if there is one.
        Context baseContext = appContext;
        String pkgName = SystemProperties.get("debug.second-display.pkg");
        if (pkgName != null && !pkgName.isEmpty()
                && r.packageInfo.mPackageName.contains(pkgName)) {
            DisplayManagerGlobal dm = DisplayManagerGlobal.getInstance();
            for (int displayId : dm.getDisplayIds()) {
                if (displayId != Display.DEFAULT_DISPLAY) {
                    Display display = dm.getRealDisplay(displayId, r.token);
                    baseContext = appContext.createDisplayContext(display);
                    break;
                }
            }
        }
        return baseContext;
    }
...

上面这段话的意思是new 一个ContextImp，并且把它附到新创建的Activity里面，我们来看看ContextImp的init方法究竟做了什么

    final void init(LoadedApk packageInfo, IBinder activityToken, ActivityThread mainThread,
            Resources container, String basePackageName, UserHandle user) {
        mPackageInfo = packageInfo;
        if (basePackageName != null) {
            mBasePackageName = mOpPackageName = basePackageName;
        } else {
            mBasePackageName = packageInfo.mPackageName;
            ApplicationInfo ainfo = packageInfo.getApplicationInfo();
            if (ainfo.uid == Process.SYSTEM_UID && ainfo.uid != Process.myUid()) {
                // Special case: system components allow themselves to be loaded in to other
                // processes.  For purposes of app ops, we must then consider the context as
                // belonging to the package of this process, not the system itself, otherwise
                // the package+uid verifications in app ops will fail.
                mOpPackageName = ActivityThread.currentPackageName();
            } else {
                mOpPackageName = mBasePackageName;
            }
        }
        mResources = mPackageInfo.getResources(mainThread);
        mResourcesManager = ResourcesManager.getInstance();

        CompatibilityInfo compatInfo =
                container == null ? null : container.getCompatibilityInfo();
        if (mResources != null &&
                ((compatInfo != null && compatInfo.applicationScale !=
                        mResources.getCompatibilityInfo().applicationScale)
                || activityToken != null)) {
            if (DEBUG) {
                Log.d(TAG, "loaded context has different scaling. Using container's" +
                        " compatiblity info:" + container.getDisplayMetrics());
            }
            if (compatInfo == null) {
                compatInfo = packageInfo.getCompatibilityInfo();
            }
            mDisplayAdjustments.setCompatibilityInfo(compatInfo);
            mDisplayAdjustments.setActivityToken(activityToken);
            mResources = mResourcesManager.getTopLevelResources(mPackageInfo.getResDir(),
                    Display.DEFAULT_DISPLAY, null, compatInfo, activityToken);
        } else {
            mDisplayAdjustments.setCompatibilityInfo(packageInfo.getCompatibilityInfo());
            mDisplayAdjustments.setActivityToken(activityToken);
        }
        mMainThread = mainThread;
        mActivityToken = activityToken;
        mContentResolver = new ApplicationContentResolver(this, mainThread, user);
        mUser = user;
    }

嗯，resource终于出现了！

二、Resource的创建