ILJMALL project過程中遇到Fragment嵌套問題:IllegalArgumentException: Binary XML file line #23: Duplicate id

• 出現場景:當點擊“分類”再返回“首頁”時，發生error退出
• 

• BUG描述：Caused by: java.lang.IllegalArgumentException: Binary XML file line #23: Duplicate id 0x7f0d0054, tag null, or parent id 0xffffffff with another fragment for com.example.sxq123.iljmall.FragmentCatagorySpace

• //framgment_home.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <ScrollView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1">
        <LinearLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text = "@string/home"/>

<fragment
    android:id = "@+id/fragment_space"
    android:name = "com.example.sxq123.iljmall.FragmentCatagorySpace"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"/>

</LinearLayout>
</ScrollView>
</LinearLayout>

• //FragmentHome.java

public class FragmentHome extends Fragment {

    private View view;
    FragmentCatagorySpace fragmentCatagorySpace ;

    @Override
    public View onCreateView(LayoutInflater inflater , ViewGroup container , Bundle savedInsataceState){
        view = inflater.inflate(R.layout.fragment_home, null);
        Log.d(this.getClass().getName(),"  onCreateView() Begin");
        initChildFragment();

        return view;
    }
    private void initChildFragment(){
        Log.d("-------------------","init space ");
        fragmentCatagorySpace = (FragmentCatagorySpace)getChildFragmentManager().findFragmentById(R.id.fragment_space);
        if(fragmentCatagorySpace != null){
            Log.d("----------------","init space success and no null");
        }
    }
}

• 問題原因

• 修正後的代碼

public class FragmentHome extends Fragment {

    private View view;
    FragmentCatagorySpace fragmentCatagorySpace ;

    @Override
    public View onCreateView(LayoutInflater inflater , ViewGroup container , Bundle savedInsataceState){
        view = inflater.inflate(R.layout.fragment_home, null);
        Log.d(this.getClass().getName(),"  onCreateView() Begin");
        initChildFragment();

        return view;
    }
@Override
public void onDestroyView(){
    super.onDestroyView();
    if(fragmentCatagorySpace != null){
        Log.d("-------------------", "space no null");
        FragmentManager fragmentManager = getFragmentManager();
        if(fragmentManager != null && !fragmentManager.isDestroyed()){
            final FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction ();
            if(fragmentTransaction != null){
                fragmentTransaction.remove(fragmentCatagorySpace).commit();
                //commit()和commitAllowingStateLoss()都是先發送到主線程任務隊列中， 當主線程準備好了再執行，非同步。
                // //如果沒有在inflate之前執行remove child fragmetn 的transaction，將會發生duplicate id 的exception !!!
//                fragmentTransaction.commit();//可以放在onCreateView中執行commit()，但偶爾會發生onSaveInstanceState()之後不能執行commit()的衝突
                fragmentTransaction.commitAllowingStateLoss();
                //立即執行任務隊列中的transaction， 不非同步 !!!!!!!!!!!!!!!重點!!!!!!!!!!!!!!!!!!!!
//防止remove事務被加到主線程任務隊列中，那這樣非同步的話可能這些事物直到父Fragment重新執行onCreateView()
//之前都沒有執行完，同樣會發生duplicate id 的異常
//如果這些remove 的食物放在父Fragment的onSaveInstanceState()中執行， 由於onSaveInstanceState()調用並不
//是每一個Fragment生命周期都會被調用(？？？？)，所以偶爾也會發生duplicate id  的異常
 fragmentManager.executePendingTransactions();
                Log.d("------------------","  space destroy");
            }
        }
    }
}
    private void initChildFragment(){
        Log.d("-------------------","init space ");
        fragmentCatagorySpace = (FragmentCatagorySpace)getChildFragmentManager().findFragmentById(R.id.fragment_space);
        if(fragmentCatagorySpace != null){
            Log.d("----------------","init space success and no null");
        }
    }
}