Question

我创建了一个显示默认布局的RecyclerView列表。然后我在列表中添加一个新项目，并更新布局以显示新项目（CardView）。然后我导航回到之前的活动。当我返回到RecyclerView活动时，我返回到通用的默认列表，我的新CardView项目没有显示。

我在Activity中有正常的onCreate（Bundle savedInstanceState）代码。似乎适配器在返回时只创建一个新的RecyclerView列表，而不是返回到先前创建的列表。我在这里缺少什么？

的活动：

public class ListContactsActivity extends AppCompatActivity {

private ListContactsAdapter mContactsAdapter;
private RecyclerView mRecyclerView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_recyclerviewlist);

    final List<Contact> mContacts;
    mContacts = new ArrayList<>();

    mRecyclerView = (RecyclerView) findViewById(R.id.cardList);
    mRecyclerView.setHasFixedSize(true);
    mRecyclerView.setLayoutManager(new LinearLayoutManager(this));

    mContactsAdapter = new ListContactsAdapter(this, mContacts);
    mContactsAdapter.setOnItemTapListener(new ListContactsAdapter.OnItemTapListener() {
        @Override
        public void onItemTap(Contact contact, int position) {
            mContactsAdapter.removeItem(contact, position);
        }
    });
    mRecyclerView.setAdapter(mContactsAdapter);
    ...

适配器：

 public class ListContactsAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

private static class EmptyViewHolder extends RecyclerView.ViewHolder {
    public EmptyViewHolder(View itemView) {
        super(itemView);
    }
}

private class ContactViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

    TextView cardBlankText2;

    public ContactViewHolder(View itemView) {
        super(itemView);
        cardBlankText2 = (TextView) itemView.findViewById(R.id.cardBlankText2);
        itemView.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        if (mOnItemTapListener != null) {
            Contact contact = mContacts.get(getLayoutPosition());
            mOnItemTapListener.onItemTap(contact, getLayoutPosition());
        }
    }
}

private Context mContext;
private LayoutInflater mLayoutInflater;

private List<Contact> mContacts;
private List<ListItem> mItems;

private OnItemTapListener mOnItemTapListener;

public ListContactsAdapter(Context context, List<Contact> contacts) {
    mContext = context;
    mLayoutInflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    mContacts = contacts;
    mItems = buildItemsList();
}

public void setOnItemTapListener(OnItemTapListener listener) {
    mOnItemTapListener = listener;
}

private List<ListItem> buildItemsList() {
    List<ListItem> items = new ArrayList<>();
    if (mContacts.size() > 0) {
        for (Contact contact : mContacts) {
            items.add(new ContactItem(contact));
        }
    } else {
        // when R. list is first created or when the number of cards
        // is deleted until there are zero, show the defaultcard_layout
        // and "Click the + above to get started".
        for (int i=0; i<1; i++) {
            items.add(new EmptyItem());
        }
    }
    return items;
}

public void addItem(Contact contact) {
    if (mContacts.size()==0) {
        // if list is empty 
        // remove empty cards first
        mItems.clear();
        notifyDataSetChanged();
    }

    // add item on the top of the list and scroll to the top position
    mContacts.add(contact);
    mItems.add(new ContactItem(contact));
    notifyItemInserted(0);
}

public void removeItem(Contact contact, int position) {
    mContacts.remove(contact);
    if (mContacts.size()==0) {
        // if no more contacts in list,
        // rebuild from scratch
        mItems.clear();
        mItems.addAll(buildItemsList());
        notifyDataSetChanged();
    } else {
        // else remove one item
        mItems.remove(position);
        notifyItemRemoved(position);
    }
}

@Override
public int getItemCount() {
    return mItems.size();
}

@Override
public int getItemViewType(int position) {
    return mItems.get(position).getType();
}

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    if (viewType == ListItem.EMPTY_TYPE) {
        View itemView = mLayoutInflater.inflate(R.layout.defaultcard_layout, parent, false);
        return new EmptyViewHolder(itemView);
    } else {
        View itemView = mLayoutInflater.inflate(R.layout.singlecard_layout, parent, false);
        return new ContactViewHolder(itemView);
    }
}

@Override
public void onBindViewHolder(final RecyclerView.ViewHolder viewHolder, final int position) {
    int type = getItemViewType(position);
    if (type == ListItem.CONTACT_TYPE) {
        ContactItem item = (ContactItem) mItems.get(position);
        final Contact contact = item.getContact();
        ContactViewHolder holder = (ContactViewHolder) viewHolder;
        holder.cardBlankText2.setText(contact.getName() + " " + contact.getSurname());
    }
}
}

Answer 1

当活动通过向后导航从堆栈中弹出时，它不会保留其任何视图或状态。活动对象及其所有视图和状态都将被销毁。如果你需要以某种方式保存活动正在做什么并且需要恢复它，你需要编写代码来做到这一点。

Android：为什么在导航回列表后销毁RecyclerView列表？

1 个答案: