activitygroup 切換動畫效果如何實現

**一下提供偽代碼，僅說明自己的理解，思路**/
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/*假設*/
AActivity,BActivity,CActivity,DActivity 都extends ActivityGroup.
A1Activity,B1Activity,C1Activity,D1Activity 都extends Activity.
A2Activity,B2Activity,C2Activity,D2Activity 都extends Activity

/*一，AActivity繼承了Activity，調用startActivity()的時候會在tab內部contentView顯示A1Activity*/
AActivity.this.startActivity(A1Activity.class)
BActivity.this.startActivity(B1Activity.class)
CActivity.this.startActivity(C1Activity.class)
DActivity.this.startActivity(D1Activity.class)

/*二，A1Activity沒有繼承ActivityGroup，所以調用startActivity()的時候和普通的調用沒有區別，A2會填滿窗口*/
A1Activity.this.startActivity(A2Activity.class)
B1Activity.this.startActivity(B2Activity.class)
C1Activity.this.startActivity(C2Activity.class)
D1Activity.this.startActivity(D2Activity.class)

/*三，A1Activity.this.getParent()獲得的是AActivity, 其實就是ActivityGroup； 雖然A1Activity沒有繼承ActivityGroup，但是A2Activity實際是由A1Activity的父類AActivity啟動的,所以A2Activity的啟動效果和一差不多*/
A1Activity.this.getParent().startActivity(A2Activity.class)
B1Activity.this.getParent().startActivity(B2Activity.class)
C1Activity.this.getParent().startActivity(C2Activity.class)
D1Activity.this.getParent().startActivity(D2Activity.class)