java - 为什么 ArrayAdapter 中的原始数组项也会被删除？

Question

我通过适配器的add()和clear()从适配器对象中添加和删除值，它们正在删除和添加元素到列表中，该列表不会从适配器内的任何位置引用。我有原始列表，它位于适配器外部，并且具有从适配器内部到不更改外部引用的引用，并且在适配器内部我仅引用了一个新列表，我使用旧的填充该列表具有相同对象的原始列表。为什么新列表会影响旧列表？

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;
    }

    private Filter myFilter = new Filter() {
        @Override
        protected FilterResults performFiltering(CharSequence constraint) {
            FilterResults filterResults = new FilterResults();
            ArrayList<com.anysoftkeyboard.ui.settings.LanguageItem> tempList=new ArrayList<com.anysoftkeyboard.ui.settings.LanguageItem>();
            //constraint is the result from text you want to filter against.
            //objects is your data set you will filter from
            if(constraint != null) {
                int length= origList.size();
                int i=0;
                while(i<length){
                    LanguageItem item= origList.get(i);
                    if(item.toString().toUpperCase().contains(constraint.toString().toUpperCase())) {
                        tempList.add(item);
                    }
                    i++;
                }
                //following two lines is very important
                //as publish result can only take FilterResults objects
                filterResults.values = tempList;
                filterResults.count = tempList.size();
            }

            return filterResults;
        }

        //HERE ARE THE AFFECTING METHODS:
        @Override
        protected void publishResults(CharSequence constraint, FilterResults results) {
            filteredList.clear();

            clear(); //******THIS METHOD REMOVES THE VALUES from origList as well******
            filteredList.addAll((Collection<? extends LanguageItem>) results.values);
            notifyDataSetChanged();

            //*****THIS ADDS VALUES TO ORIG LIST AS WELL. WHY?*****
            for(LanguageItem item: filteredList)
                add(item); 

        }
    };

    @Override
    public Filter getFilter() {
        return myFilter;
    }
}

为什么原始列表会被编辑，而我只更改过滤后的列表？

编辑:

ArrayAdapter<com.anysoftkeyboard.ui.settings.LanguageItem> adapter = new LanguageItemArrayAdapter(getContext(), simpleLanguageItems, simpleLanguageItems);
    ((LanguageItemArrayAdapter) adapter).fillData();;

(我知道修复方法，但我不明白原因 - 如果您像我一样遇到自定义适配器过滤器的问题，则修复方法位于下面的代码中。)

Answer 1

此代码将 ArrayList 的相同实例传递给 LanguageItemArrayAdapter

new LanguageItemArrayAdapter(getContext(), simpleLanguageItems, simpleLanguageItems)

要理解为什么 ArrayAdapter 中的 add(…) 和 clear() 也会修改同一个对象，您需要查看它们的实现source .

public void clear() {
    synchronized (mLock) {
        if (mOriginalValues != null) {
            mOriginalValues.clear();
        } else {
            mObjects.clear();
        }
        …
    }
    …
}

clear() 将修改 mObjects 和 mOriginalValues (您会注意到 ArrayAdapter 中的其他函数执行以下操作:相同的)。您需要阅读 ArrayFilter 内的代码以了解它们是如何修改的。

private class ArrayFilter extends Filter {
  /* 
  mObjects will contain only items fulfilling the filter conditions. 
  Original items are copied into mOriginalValues 
  */
}

查看构造函数(和构造函数链)，您会发现您的类构造函数具有

super(context, 0, filteredList);

最终会调用

private ArrayAdapter(@NonNull Context context, 
        @LayoutRes int resource,
        @IdRes int textViewResourceId, 
        @NonNull List<T> objects, 
        boolean objsFromResources) {
    …
    mObjects = objects;
    …
}

这允许ArrayAdapter修改您的simpleLanguageItems实例。