Question

我想显示4种不同类型布局的通知列表。将有4种类型的通知chat_noti，share_noti，coorganizer_noti，invitation_noti。这4种类型有4种不同的布局。我想在recyclerview中展示这一点。

这是我的适配器：

编辑：

List<Notifications> notificationsList;
Context context;
private static final int INVITATION_NOTI = 0;
private static final int CHAT_NOTI = 1;
private static final int SHARE_NOTI = 2;
private static final int COORGANIZER_NOTI = 3;
private int selectedPos = 0;
public NotificationsAdapter(Context context,List<Notifications> notificationsList){
    this.notificationsList = notificationsList;
    this.context = context;
}

@Override
public int getItemViewType(int type) {

    if (type == 0)
    {
        return INVITATION_NOTI;
    }
    else if(type == 1)
    {
        return CHAT_NOTI;
    }
    else if(type == 2)
    {
        return SHARE_NOTI;
    }
    else if (type == 3)
    {
        return COORGANIZER_NOTI;
    }

    return -1;

}

@Override
public MainViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    switch (viewType){
        case INVITATION_NOTI:
            return new InvitationViewHolder(LayoutInflater.from(context).inflate(R.layout.invitation_notification, parent, false));
        case CHAT_NOTI:
            return new ChatNotificationViewHolder(LayoutInflater.from(context).inflate(R.layout.chat_notification, parent, false));
        case SHARE_NOTI:
            return new ShareViewHolder(LayoutInflater.from(context).inflate(R.layout.share_notification, parent, false));
        case COORGANIZER_NOTI:
            return new CoOrganizerViewHolder(LayoutInflater.from(context).inflate(R.layout.co_organizer_notification, parent, false));
    }
    return null;
}

@Override
public void onBindViewHolder(MainViewHolder holder, int position) {
    if(holder.getItemViewType() == INVITATION_NOTI){
        InvitationViewHolder  mholder = (InvitationViewHolder) holder;
    }
    else if(holder.getItemViewType() == CHAT_NOTI){
        ChatNotificationViewHolder  mholder = (ChatNotificationViewHolder) holder;
    }
    else if(holder.getItemViewType() == SHARE_NOTI){
        ShareViewHolder  mholder = (ShareViewHolder) holder;
    }
    else if(holder.getItemViewType() == COORGANIZER_NOTI){
        CoOrganizerViewHolder mholder = (CoOrganizerViewHolder) holder;
    }
}



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

public class InvitationViewHolder extends MainViewHolder{
    TextView text,event,question;
    Button yes,no;

    public InvitationViewHolder(View v){
        super(v);
        this.text = (TextView) v.findViewById(R.id.text);
        this.event = (TextView) v.findViewById(R.id.eventType);
        this.question = (TextView) v.findViewById(R.id.question);
        this.yes = (Button) v.findViewById(R.id.yes);
        this.no = (Button) v.findViewById(R.id.no);
    }
}

public class ChatNotificationViewHolder extends MainViewHolder{
    TextView text,sender;

    public ChatNotificationViewHolder(View v){
        super(v);
        this.text = (TextView) v.findViewById(R.id.text);
        this.sender = (TextView) v.findViewById(R.id.sender);
    }
}
public class ShareViewHolder extends MainViewHolder{
    TextView text;

    public ShareViewHolder(View v){
        super(v);
        this.text = (TextView) v.findViewById(R.id.text);
    }
}
public class CoOrganizerViewHolder extends MainViewHolder{
    TextView text;
    Button view;

    public CoOrganizerViewHolder(View v){
        super(v);
        this.text = (TextView) v.findViewById(R.id.text);
        this.view = (Button)  v.findViewById(R.id.view);
    }
}

public class MainViewHolder extends  RecyclerView.ViewHolder {
    public MainViewHolder(View v) {
        super(v);
    }
}

LogCat：

致命的例外：主要处理：com.example.siddhi.meavita，PID：22717 java.lang.NullPointerException：尝试在空对象引用上写入字段'int android.support.v7.widget.RecyclerView $ ViewHolder.mItemViewType' 在android.support.v7.widget.RecyclerView $ Adapter.createViewHolder（RecyclerView.java:5483）在android.support.v7.widget.RecyclerView $ Recycler.getViewForPosition（RecyclerView.java:4707）在android.support.v7.widget.RecyclerView $ Recycler.getViewForPosition（RecyclerView.java:4617）在android.support.v7.widget.LinearLayoutManager $ LayoutState.next（LinearLayoutManager.java:1994）在android.support.v7.widget.LinearLayoutManager.layoutChunk（LinearLayoutManager.java:1390）在android.support.v7.widget.LinearLayoutManager.fill（LinearLayoutManager.java:1353）

我尝试使用此代码，它为视图类型抛出空指针异常。

根据通知类型，应显示布局。我怎样才能做到这一点？谢谢..

我正在添加这样的项目：

  private void prepareData() {

    Notifications notifications = new Notifications("You have an Invitation.","Michell's Marraige","Attending?","",0);
    notificationsList.add(notifications);

    notifications = new Notifications("You have an Invitation.","Kate's Reception","Attending?","",0);
    notificationsList.add(notifications);

    notifications = new Notifications("Vishal Say's","","Have you attended wedding?","",1);
    notificationsList.add(notifications);


    notifications = new Notifications("Siddhi Say's","","Have you gone for shopping?","",1);
    notificationsList.add(notifications);

    notifications = new Notifications("Ashmit shared a photo with you","","","",2);
    notificationsList.add(notifications);

    notifications = new Notifications("Neeta shared a photo with you","","","",2);
    notificationsList.add(notifications);

    notifications = new Notifications("You are a co-organizer for My Birthaday","","","",3);
    notificationsList.add(notifications);

    notifications = new Notifications("You are a co-organizer for My Wedding","","","",3);
    notificationsList.add(notifications);

    mAdapter.notifyDataSetChanged();


}

最后一个属性是通知类型。

Answer 1

当getItemViewType()返回onCreateViewHolder尚未为视图所有者分配的值时，会导致此错误。我觉得发生的事情是getItemViewType()返回-1表示某个值。现在，onCreateViewHolder()在viewType == -1时不知道该怎么做。因此，您收到了错误。

Answer 2

在我的情况下，当我忘记在onCreateViewHolder方法的一部分中返回视图持有者时，我收到此错误，并且它在方法结束时落入“return null”语句。

Answer 3

@Override
public int getItemViewType(int position) {
    if (position != -1) {
        return 0;
    }
    return -1;
}

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    if (viewType != -1) {
        return new GroupImageViewHolder(mInflater.inflate(R.layout.group_image_item_view, parent, false));
    }
    return null;
}


@Override
public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
    if (viewHolder != null) {
        // do whatever you want to do...

}

Answer 4

@soku和@Jason Tyler是对的。我有一次遇到同样的问题，但原因是我在onCreateViewHolder方法中返回'null'。我将其更改为我的默认ViewHolder的新实例，并且它有效。

如何在recyclerView中显示不同的布局？

4 个答案: