Activity的performStart用于执行ActivityStart，代码如下：

//frameworks/base/core/java/android/app/Activity.java
public class Activity extends ContextThemeWrapper
        implements LayoutInflater.Factory2,
        Window.Callback, KeyEvent.Callback,
        OnCreateContextMenuListener, ComponentCallbacks2,
        Window.OnWindowDismissedCallback,
        ContentCaptureManager.ContentCaptureClient {
    final void performStart(String reason) {
        dispatchActivityPreStarted();
        mActivityTransitionState.setEnterActivityOptions(this, getActivityOptions());
        mFragments.noteStateNotSaved();
        mCalled = false;
        mFragments.execPendingActions();
        mInstrumentation.callActivityOnStart(this);
        EventLogTags.writeWmOnStartCalled(mIdent, getComponentName().getClassName(), reason);


        if (!mCalled) {
            throw new SuperNotCalledException(
                "Activity " + mComponent.toShortString() +
                " did not call through to super.onStart()");
        }
        mFragments.dispatchStart();
        mFragments.reportLoaderStart();


        // Warn app developers if the dynamic linker logged anything during startup.
        boolean isAppDebuggable =
                (mApplication.getApplicationInfo().flags & ApplicationInfo.FLAG_DEBUGGABLE) != 0;
        if (isAppDebuggable) {
            String dlwarning = getDlWarning();
            if (dlwarning != null) {
                String appName = getApplicationInfo().loadLabel(getPackageManager())
                        .toString();
                String warning = "Detected problems with app native libraries\n" +
                                 "(please consult log for detail):\n" + dlwarning;
                if (isAppDebuggable) {
                      new AlertDialog.Builder(this).
                          setTitle(appName).
                          setMessage(warning).
                          setPositiveButton(android.R.string.ok, null).
                          setCancelable(false).
                          show();
                } else {
                    Toast.makeText(this, appName + "\n" + warning, Toast.LENGTH_LONG).show();
                }
            }
        }


        GraphicsEnvironment.getInstance().showAngleInUseDialogBox(this);


        mActivityTransitionState.enterReady(this);
        dispatchActivityPostStarted();
    }
}

上面方法主要处理如下：

1、调用mInstrumentation(Instrumentation)的callActivityOnStart方法。

2、调用dispatchActivityPostStarted方法。

下面分别进行分析：

Instrumentation callActivityOnStart

调用mInstrumentation(Instrumentation)的callActivityOnStart方法：

//frameworks/base/core/java/android/app/Instrumentation.java
public class Instrumentation {
    public void callActivityOnStart(Activity activity) {
        activity.onStart();
    }
}

Activity onStart

调用Activity的onStart方法：

void onStart()：在 {@link #onCreate} 之后调用，或者在 {@link #onRestart} 之后调用，当活动已停止时，但现在再次向用户显示。

在其子类(应用程序实现)的onStart会调用super.onStart()方法：

//frameworks/base/core/java/android/app/Activity.java
public class Activity extends ContextThemeWrapper
        implements LayoutInflater.Factory2,
        Window.Callback, KeyEvent.Callback,
        OnCreateContextMenuListener, ComponentCallbacks2,
        Window.OnWindowDismissedCallback,
        ContentCaptureManager.ContentCaptureClient {
    protected void onStart() {
        if (DEBUG_LIFECYCLE) Slog.v(TAG, "onStart " + this);
        mCalled = true;


        mFragments.doLoaderStart();


        dispatchActivityStarted();


        getAutofillClientController().onActivityStarted();
    }
}

Activity dispatchActivityStarted

调用Activity的dispatchActivityStarted方法：

//frameworks/base/core/java/android/app/Activity.java
public class Activity extends ContextThemeWrapper
        implements LayoutInflater.Factory2,
        Window.Callback, KeyEvent.Callback,
        OnCreateContextMenuListener, ComponentCallbacks2,
        Window.OnWindowDismissedCallback,
        ContentCaptureManager.ContentCaptureClient {
    private void dispatchActivityStarted() {
        getApplication().dispatchActivityStarted(this);
        Object[] callbacks = collectActivityLifecycleCallbacks();
        if (callbacks != null) {
            for (int i = 0; i < callbacks.length; i++) {
                ((Application.ActivityLifecycleCallbacks) callbacks[i]).onActivityStarted(this);
            }
        }
    }
}

Application.ActivityLifecycleCallbacks onActivityStarted

调用Application.ActivityLifecycleCallbacks的onActivityStarted方法，如果应用程序调用了Application的registerActivityLifecycleCallbacks，就会收到onActivityStarted回调。

void onActivityCreated(@NonNull Activity activity, @Nullable Bundle savedInstanceState)：在 Activity 调用 {@link Activity#onCreate super.onCreate（）} 时调用。

Activity dispatchActivityPostStarted

调用Activity的dispatchActivityPostStarted方法：

//frameworks/base/core/java/android/app/Activity.java
public class Activity extends ContextThemeWrapper
        implements LayoutInflater.Factory2,
        Window.Callback, KeyEvent.Callback,
        OnCreateContextMenuListener, ComponentCallbacks2,
        Window.OnWindowDismissedCallback,
        ContentCaptureManager.ContentCaptureClient {
    private void dispatchActivityPostStarted() {
        Object[] callbacks = collectActivityLifecycleCallbacks();
        if (callbacks != null) {
            for (int i = 0; i < callbacks.length; i++) {
                ((Application.ActivityLifecycleCallbacks) callbacks[i])
                        .onActivityPostStarted(this);
            }
        }
        getApplication().dispatchActivityPostStarted(this);
    }
}

Application.ActivityLifecycleCallbacks onActivityPostStarted

调用Application.ActivityLifecycleCallbacks的onActivityPostStarted方法，如果应用程序调用了Application的registerActivityLifecycleCallbacks，就会收到onActivityPostStarted回调。

void onActivityPostStarted(@NonNull Activity activity)：作为正在启动的活动的最后一步调用。这始终在 {@link Activity#onStart} 之后调用。