Firebase获取最后一个生成null的子项[重复](Firebase get last child producing null [duplicate])
这个问题在这里已经有了答案:
如何从dataSnapshot获取价值? 2个答案我正在使用Firebase,我想获得最后一个密钥(消息)。 但是我的代码只是生产NPE。 fb数据库的结构可以在这里看到:
Query lastQuery = rootRef.child("Chatmessages").child(last).child(userid).orderByKey().limitToLast(1); lastQuery.addListenerForSingleValueEvent(new ValueEventListener() { @Override public void onDataChange(DataSnapshot dataSnapshot) { String message = dataSnapshot.child("message").getValue().toString(); // Error on this line // viewHolder.setUserStatus(message); } @Override public void onCancelled(DatabaseError databaseError) { } });This question already has an answer here:
How get value from dataSnapshot? 2 answersI am using Firebase and I would like to get the last key (message). However with my code it is just producing NPE. The structure of the fb database can be seen here:
Query lastQuery = rootRef.child("Chatmessages").child(last).child(userid).orderByKey().limitToLast(1); lastQuery.addListenerForSingleValueEvent(new ValueEventListener() { @Override public void onDataChange(DataSnapshot dataSnapshot) { String message = dataSnapshot.child("message").getValue().toString(); // Error on this line // viewHolder.setUserStatus(message); } @Override public void onCancelled(DatabaseError databaseError) { } });最满意答案
查询返回一个数组而不是单个对象,因此您应该遍历dataSnapShot以获取它拥有的唯一对象:上次聊天...
@Override public void onDataChange(DataSnapshot dataSnapshot) { for (DataSnapshot child: dataSnapshot.getChildren()) { String message = child.child("message").getValue().toString(); // viewHolder.setUserStatus(message); } }The query returns an array and not a single object, so you should loop over the dataSnapShot to get the only object it has: the last chat...
@Override public void onDataChange(DataSnapshot dataSnapshot) { for (DataSnapshot child: dataSnapshot.getChildren()) { String message = child.child("message").getValue().toString(); // viewHolder.setUserStatus(message); } }更多推荐
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