我正在构建一个事件应用程序，这是每个事件的卡片模型：
现在这是我数据库中的事件数据 . 我有一个 "events" 节点（包含每个事件项）和一个 "events-users" 节点（包含参加该事件的每个用户项） .
要获取基本事件项（图像和名称），我有一个FirebaseRecyclerAdapter，它运行良好：
/**** EVENTS EVENTS EVENTS EVENTS ****/
// Inflates events
RecyclerView mEventsRecyclerView = (RecyclerView) findViewById(R.id.activity_zone_events_recyclerview);
mEventsRecyclerView.setLayoutManager(new GridLayoutManager(ZoneActivity.this, 1));
DatabaseReference events = fDatabaseRoot.child("events");
mEventsAdapter = new FirebaseRecyclerAdapter<EventItem, EventItemHolder>(EventItem.class, R.layout.item_event, EventItemHolder.class, events) {
@Override
protected void populateViewHolder(final EventItemHolder eventItemHolder, final EventItem event, final int position) {
// Sets event image
eventItemHolder.setEventImage(event.getEventImage());
// Sets event name
eventItemHolder.setEventName(event.getEventName());
// Sets event OnClickListener
eventItemHolder.eventCard.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// Opens EventActivity
Intent eventActivity = new Intent(ZoneActivity.this, EventActivity.class);
startActivity(eventActivity);
}
}
});
};
mEventsRecyclerView.setAdapter(mEventsAdapter);
problem 是我不知道如何获取每张卡内的用户项目（与会者） . 我尝试在我创建的FirebaseRecyclerAdapter中初始化另一个FirebaseRecyclerAdapter，但是当我打开相应的活动时应用程序中断...这是我尝试过的：
/**** EVENTS EVENTS EVENTS EVENTS ****/
// Inflates events
RecyclerView mEventsRecyclerView = (RecyclerView) findViewById(R.id.activity_zone_events_recyclerview);
mEventsRecyclerView.setLayoutManager(new GridLayoutManager(ZoneActivity.this, 1));
DatabaseReference events = fDatabaseRoot.child("events");
mEventsAdapter = new FirebaseRecyclerAdapter<EventItem, EventItemHolder>(EventItem.class, R.layout.item_event, EventItemHolder.class, events) {
@Override
protected void populateViewHolder(final EventItemHolder eventItemHolder, final EventItem event, final int position) {
// Sets event image
eventItemHolder.setEventImage(event.getEventImage());
// Sets event name
eventItemHolder.setEventName(event.getEventName());
// Sets event OnClickListener
eventItemHolder.eventCard.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// Opens EventActivity
Intent eventActivity = new Intent(ZoneActivity.this, EventActivity.class);
startActivity(eventActivity);
}
/**** EVENT-ATTENDEES EVENT-ATTENDEES EVENT-ATTENDEES EVENT-ATTENDEES ****/
// Inflates event's attendees
RecyclerView mAttendeesRecyclerView = (RecyclerView) findViewById(R.id.item_event_attendees_recyclerview);
mAttendeesRecyclerView.setLayoutManager(new GridLayoutManager(ZoneActivity.this, 1));
mAttendeesAdapter = new FirebaseRecyclerAdapter<UserItem, UserItemHolder>(UserItem.class, R.layout.item_user, UserItemHolder.class, fDatabaseRoot.child("zones-events").child(zoneKey)) {
@Override
protected void populateViewHolder(final UserItemHolder userItemHolder, final UserItem user, final int position) {
// Sets attendee image
userItemHolder.setUserImage(user.getUserImage());
}
};
mAttendeesRecyclerView.setAdapter(mAttendeesAdapter);
}
};
mEventsRecyclerView.setAdapter(mEventsAdapter);
这是 error ：
02-27 19:18:53.783 1050-1050/? E/UncaughtException: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at com.whatudu.whatudu.ZoneActivity$2$1$1.populateViewHolder(ZoneActivity.java:208)
at com.whatudu.whatudu.ZoneActivity$2$1$1.populateViewHolder(ZoneActivity.java:141)
at com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:184)
at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:5825)
at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:5858)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5094)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4970)
at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2029)
at android.support.v7.widget.GridLayoutManager.layoutChunk(GridLayoutManager.java:541)
at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1377)
at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:578)
at android.support.v7.widget.GridLayoutManager.onLayoutChildren(GridLayoutManager.java:170)
at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3315)
at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:2843)
任何形式的帮助或提示（如果之前有人这样做过）将非常感谢！我知道这是可能的，我只是不知道该怎么做！ :(
非常感谢你提前 .
附：选择GridLayoutManager作为布局样式，因为这是我以前做的 .