ActivityThread performLaunchActivity

ActivityThread performLaunchActivity

今天就想单独分析下这个函数，理解这个函数对于我们理解Activity的生命周期还是很有帮助的，这个函数真正执行了Activity的创建，并执行了onCreate函数。

新建Activity对象

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent)
    ActivityInfo aInfo = r.activityInfo;
    ......

    ComponentName component = r.intent.getComponent();
    ......

    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);
        }
    }  

这部分很好理解，就是使用反射方法，新建了activity对象

attach

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 (r.overrideConfig != null) {
        config.updateFrom(r.overrideConfig);
    }
    if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "
            + r.activityInfo.name + " with config " + config);
    Window window = null;
    if (r.mPendingRemoveWindow != null && r.mPreserveWindow) {
        window = r.mPendingRemoveWindow;
        r.mPendingRemoveWindow = null;
        r.mPendingRemoveWindowManager = null;
    }
    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);  

这段代码一开始就让人感觉有点懵

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

咋一看感觉新建了一个Application对象，其实不然，可以看下makeApplication函数的实现：

public Application makeApplication(boolean forceDefaultAppClass,
        Instrumentation instrumentation) {
    if (mApplication != null) {
        return mApplication;
    }  

我只截取了最开始的代码，由于在执行创建Activity逻辑时mApplication对象已经创建，故这段代码会直接返回应用进程创建时新建的Application对象。

再回到attach的逻辑，接下来系统创建了Activity的appContext，获取了Activity的title，最后执行了attach函数，注意，此时还没有执行Activity的onCreate函数。看下attach函数的参数，getInstrumentation，r.intent……，可以发现在Activity执行onCreate函数之前，Activity的属性已经被设置了。

onCreate

int theme = r.activityInfo.getThemeResource();
if (theme != 0) {
    activity.setTheme(theme);
}

activity.mCalled = false;
if (r.isPersistable()) {
    mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
    mInstrumentation.callActivityOnCreate(activity, r.state);
}
if (!activity.mCalled) {
    throw new SuperNotCalledException(
        "Activity " + r.intent.getComponent().toShortString() +
        " did not call through to super.onCreate()");
}
......
mActivities.put(r.token, r);  

在执行onCreate函数之前，首先获取并设置Activity的Theme信息。activity.mCalled变量标识Activity生命周期的函数是否已经执行，此处用来标识onCreate是否执行。如果执行完mInstrumentation.callActivityOnCreate之后发现activity.mCalled没有被设置为true，则可以认为Activity的onCreate没有被执行，系统抛出异常。最后将代表Activity的ActivityRecord保存在mActivities的ArrayMap结构中