您需要将filter()方法从Activity移到Adapter.在您的适配器上添加一个其他变量，以保存未过滤的数据集的副本.在您的情况下，您需要contactsList和copyOfContactsList变量.

You need to move your filter() method from your Activity to your Adapter. At your Adapter add one additional variable to hold a copy of unfiltered dataset. In your case, you need contactsList and copyOfContactsList variables.

按如下所示更改适配器的构造函数:

Change your Adapter's constructor as follows:

public class ContactsAdapter extends RecyclerView.Adapter<ContactViewHolder> {

    ....
    private ArrayList<Contact> contactsList = new ArrayList<>();
    private ArrayList<Contact> copyOfContactsList = new ArrayList<>();
    ....

    public ContactsAdapter(Context context, ArrayList<Contact> dataSet, boolean fromMyContacts){
        ...
        this.contactsList = dataSet;
        copyOfContactsList.addAll(dataSet);
        ...
    }

，这是要添加到Adapter的过滤器方法:

and this is the filter method to be added to your Adapter:

public void filter(String text) {
    if(text.isEmpty()){
        contactsList.clear();
        contactsList.addAll(copyOfContactsList);
    } else{
        ArrayList<Contact> result = new ArrayList<>();
        text = text.toLowerCase();
        for(Contact item: copyOfContactsList){
            if(item.getName().toLowerCase().contains(text)){
                result.add(item);
            }
        }
        contactsList.clear();
        contactsList.addAll(result);
    }
    notifyDataSetChanged();
}