Application 启动时长计算

时长计算 StartTime定位

查看源码，Application实例化时调用的是newApplication（）方法（具体原理参考另外一篇博客，Application启动流程分析 https://blog.csdn.net/binghelonglong123/article/details/88414051）

form Instrumentation.java    
public Application newApplication(ClassLoader cl, String className, Context context)
            throws InstantiationException, IllegalAccessException, 
            ClassNotFoundException {
        Application app = getFactory(context.getPackageName())
                .instantiateApplication(cl, className);
        app.attach(context);
        return app;
    }

Application的attach 最终调用 attachBaseContext（）

from Application.java   
 /* package */ final void attach(Context context) {
        attachBaseContext(context);
        mLoadedApk = ContextImpl.getImpl(context).mPackageInfo;
    }

因此冷启动Application的计时开始时间可以在attachBaseContext方法中进行startTime的记录

时长计算 EndTime定位

Application启动结束的时间，可以理解为应用完全启动并展示主Activity第一帧的时间

详见下面的“Activity启动到第一帧展示时长计算”

Activity启动时长计算（onCreat耗时）

以API28之前的源码为例

参考这两篇文章（这是我见过分析的最好的当然API28有变化，还没有细致研究）

https://blog.csdn.net/android_jianbo/article/details/86487752

https://blog.csdn.net/android_jianbo/article/details/86488828

Activity启动入口

    private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {

.........................................

        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);
            r.intent.prepareToEnterProcess();
            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 (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,
                        r.referrer, r.voiceInteractor);

...............................................................
                if (r.isPersistable()) {
                    mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
                } else {
                    mInstrumentation.callActivityOnCreate(activity, r.state);
                }
.............................................................
                if (!r.activity.mFinished) {
                    activity.performStart();
                    r.stopped = false;
                }
                if (!r.activity.mFinished) {
                    if (r.isPersistable()) {
                        if (r.state != null || r.persistentState != null) {
                            mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state,
                                    r.persistentState);
                        }
                    } else if (r.state != null) {
                        mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
                    }
                }
                if (!r.activity.mFinished) {
                    activity.mCalled = false;
                    if (r.isPersistable()) {
                        mInstrumentation.callActivityOnPostCreate(activity, r.state,
                                r.persistentState);
                    } else {
                        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;
    }

从上述代码中可以看出

Activity被实例化后的调用顺序是

1：实例化Activity对象

activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);

2：调用attach() 这里其实最终调用的是Activity的attachBaseContext()

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);

3：调用onCreat

mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);

4：完成create之后紧接着调用了onStart()

activity.performStart();

从上述代码中我们可以得出结论要想完成一次Activity的启动耗时记录

StartTime：Activity的attachBaseContext()

EndTime：Activity的onStart()开始调用的时候可视为Activity的onCreat()完成启动

Activity启动到开始绘制的时长计算

这个时长计算的关键地方就是如何获取开始绘制的时机

从网上查询到可以如下代码来监听绘制开始的时机

activity.getWindow().getDecorView().post(new FirstFrameRunnable(activity, startType, startTime));

具体原理，我们参照源码分析一下

DecorView 其实就继承自FramLayout

最终的post方法其实是View里面的post方法来看下源码

    public boolean post(Runnable action) {
        final AttachInfo attachInfo = mAttachInfo;
        if (attachInfo != null) {
            return attachInfo.mHandler.post(action);
        }
        // Assume that post will succeed later
        ViewRootImpl.getRunQueue().post(action);
        return true;
    }

第一个判断比较简单有AttachInfo的时候就用AttachInfo的Handler执行post 如果没有我们再看RunQueue

    /**
     * The run queue is used to enqueue pending work from Views when no Handler is
     * attached.  The work is executed during the next call to performTraversals on
     * the thread.
     * @hide
     */
static final class RunQueue {
        private final ArrayList<HandlerAction> mActions = new ArrayList<HandlerAction>();

        void post(Runnable action) {
            postDelayed(action, 0);
        }

        void postDelayed(Runnable action, long delayMillis) {
            HandlerAction handlerAction = new HandlerAction();
            handlerAction.action = action;
            handlerAction.delay = delayMillis;

            synchronized (mActions) {
                mActions.add(handlerAction);
            }
        }

        void removeCallbacks(Runnable action) {
            final HandlerAction handlerAction = new HandlerAction();
            handlerAction.action = action;

            synchronized (mActions) {
                final ArrayList<HandlerAction> actions = mActions;

                while (actions.remove(handlerAction)) {
                    // Keep going
                }
            }
        }

        void executeActions(Handler handler) {
            synchronized (mActions) {
                final ArrayList<HandlerAction> actions = mActions;
                final int count = actions.size();

                for (int i = 0; i < count; i++) {
                    final HandlerAction handlerAction = actions.get(i);
                    handler.postDelayed(handlerAction.action, handlerAction.delay);
                }

                actions.clear();
            }
        }

代码比较简单主要执行的地方在executeActions(handler)

从方法的注释里面也可以看到是在performTraversals（）方法里面调用的

performTraversals（）方法就不多说了有兴趣的同学自己去查下资料（https://www.jianshu.com/p/ada6b5f18b5d）

这里说一下网上查到的资料

View真正的绘制流程是从ViewRootImpl的performTraversals方法开始, 里面会经过measure, layout和draw三个过程. 其中

measure用来测量View的宽高, layout用来确定View的位置, 而draw负责渲染View到屏幕上

也就是说当performTraversals被调用的时候，Activity已经开始进入绘制流程了所以使用getDecorView().post()可以实现对这个时

间点的监听，同样这个原理可以用在Activity启动性能优化上面，使用getDecorView().post()方法来处理耗时操作，可以避免在

Activity启动时将Activity卡住

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