看log，可以看到正常切換fragment。為什么文字沒有改變？

這是MainActivity3的代碼：

public?class?MainActivity3?extends?Activity?{

????private?Button?button;
????private?boolean?flag?=?true;

????@Override
????protected?void?onCreate(Bundle?savedInstanceState)?{
????????super.onCreate(savedInstanceState);
????????setContentView(R.layout.main3);
????????/**
?????????*?設置fragment3顯示在layout3中
?????????*/
????????getFragmentManager().beginTransaction().add(R.id.layout3,?new?MyFragment3()).commit();
????????button?=?(Button)?findViewById(R.id.cast);
????????/**
?????????*?設置點擊事件：如果當前顯示的是fragment3，則切換到fragment4；
?????????*?????????????如果當前顯示的是fragment4，則切換回fragment3
?????????*/
????????button.setOnClickListener(new?View.OnClickListener()?{
????????????@Override
????????????public?void?onClick(View?v)?{
????????????????FragmentTransaction?transaction?=?getFragmentManager().beginTransaction();
????????????????MyFragment3?myFragment3?=?new?MyFragment3();
????????????????MyFragment4?myFragment4?=?new?MyFragment4();
????????????????if?(flag)?{
????????????????????transaction.add(R.id.layout3,?myFragment4);
????????????????????flag?=?false;
????????????????}?else?{
????????????????????transaction.add(R.id.layout3,?myFragment3);
????????????????????flag?=?true;
????????????????}
????????????????transaction.commit();
????????????}
????????});
????}

}

這是MyFragment3的onCreateView方法：

@Override
public?View?onCreateView(LayoutInflater?inflater,?ViewGroup?container,?Bundle?savedInstanceState)?{
????Log.i("Main",?"[3]onCreateView()?---->>>?fragment所包含的所有view組件創建完成");
????View?view?=?inflater.inflate(R.layout.fragment2,?container,?false);
????TextView?textView?=?(TextView)?view.findViewById(R.id.text2);
????textView.setText("第一個fragment");
????return?view;
}

這是MyFragment4的onCreateView方法：

@Override
public?View?onCreateView(LayoutInflater?inflater,?ViewGroup?container,?Bundle?savedInstanceState)?{
????Log.i("Main",?"[4]onCreateView()?---->>>?fragment所包含的所有view組件創建完成");
????View?view?=?inflater.inflate(R.layout.fragment2,?container,?false);
????TextView?textView?=?(TextView)?view.findViewById(R.id.text2);
????textView.setText("第二個fragment");
????return?view;
}

這是main3.xml：

這是fragment2.xml