Question

ActivityA is main visible activity. I want to start activityB inside activityA. And build activityB in FrameLayout (or something like that) of activityA. Is it possible? And how?

Answer 1

Yes, you can use an ActivityGroup and embedded it in there.

http://developer.android.com/reference/android/app/ActivityGroup.html

public class ActivityA extends ActivityGroup {

    ...
    Intent b = new Intent(this, ActivityB.class);
    Window bWindow = getLocalActivityManager().startActivity(ActivityB.class.getName(),b);
    activityFrame.addView(bWindow.getDecorView());  // activityFrame being your FrameLayout
    ....