我通過適配器的 add() 和 clear() 從適配器對象中添加和刪除值，它們正在刪除元素并將其添加到列表中，該列表不會從適配器內的任何位置引用。我有原始列表，它位于適配器外部，并具有從適配器內部到不更改外部引用的引用，而在適配器內部，我僅引用一個新列表，我使用舊的原始列表填充了相同的對象。新名單為何會影響舊名單？class LanguageItemArrayAdapter extends ArrayAdapter<com.anysoftkeyboard.ui.settings.LanguageItem>{ private Context mContext; private final ArrayList<com.anysoftkeyboard.ui.settings.LanguageItem> origList = new ArrayList<com.anysoftkeyboard.ui.settings.LanguageItem>(); private final ArrayList<com.anysoftkeyboard.ui.settings.LanguageItem> filteredList = new ArrayList<com.anysoftkeyboard.ui.settings.LanguageItem>(); LanguageItemArrayAdapter(@NonNull Context context, @LayoutRes ArrayList<com.anysoftkeyboard.ui.settings.LanguageItem> list, ArrayList<com.anysoftkeyboard.ui.settings.LanguageItem> filteredList){ super(context, 0, filteredList); mContext = context; origList.addAll(list); //THIS WORKS WELL. //THIS BREAKS EVERYTHING -> //origlist = list; } public void fillData(){ filteredList.addAll(origList); notifyDataSetChanged(); } @Override public View getView(int position, View convertView, @NonNull ViewGroup parent) { View listItem = convertView; if (listItem == null) listItem = LayoutInflater.from(mContext).inflate(R.layout.languages_list_row, parent, false); com.anysoftkeyboard.ui.settings.LanguageItem currentItem = filteredList.get(position); TextView title = listItem.findViewById(R.id.title); title.setText(currentItem.getTitle()); return listItem; }為什么原始列表會被編輯，而我只更改過濾后的列表？
1 回答
aluckdog
TA貢獻1847條經驗 獲得超7個贊
此代碼將相同的實例傳遞ArrayList給LanguageItemArrayAdapter
new LanguageItemArrayAdapter(getContext(), simpleLanguageItems, simpleLanguageItems)
要理解為什么add(…)和clear()in也修改同一個對象，您需要從源代碼ArrayAdapter中查看它們的實現。
public void clear() {
synchronized (mLock) {
if (mOriginalValues != null) {
mOriginalValues.clear();
} else {
mObjects.clear();
}
…
}
…
}
clear()將修改mObjects和mOriginalValues（您會注意到其他函數也ArrayAdapter做同樣的事情）。您需要閱讀里面的代碼ArrayFilter以了解它們是如何修改的。
private class ArrayFilter extends Filter {
/*
mObjects will contain only items fulfilling the filter conditions.
Original items are copied into mOriginalValues
*/
}
查看構造函數（和構造函數鏈），您會發現您的類構造函數有
super(context, 0, filteredList);
最終會調用
private ArrayAdapter(@NonNull Context context,
@LayoutRes int resource,
@IdRes int textViewResourceId,
@NonNull List<T> objects,
boolean objsFromResources) {
…
mObjects = objects;
…
}
這允許ArrayAdapter修改您的simpleLanguageItems實例。
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