我有一个Order节点和一个Status键.我正在寻找状态值的变化,如果检测到任何变化,我必须阅读父订单节点.
关键点是我不想听Order节点中的更改.但只是Order节点下的Status.最佳方式是什么？在另一个监听器中有一个监听器是否好？这是我的代码：
final Query qRef = FirebaseDatabase.getInstance().getReference().child("orders").orderByChild("customerId").equalTo(FirebaseAuth.getInstance().getCurrentUser().getUid())
.limitToFirst(1);
qRef.keepSynced(true);
final DatabaseReference reference = qRef.getRef().child("status");
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
DatabaseReference inner = reference.getParent();
inner.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot parent) {
if (parent != null) {
Order newOrder = parent.getValue(Order.class);
if (newOrder != null) {
if (newOrder.getStatus() != null && !newOrder.getStatus().equals("FX_OVER"))
processOrder(newOrder);
}
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
和JSON：
{ "20161010210955" : {
"createdAt" : {
"date" : 10,"day" : 1,"hours" : 21,"minutes" : 9,"month" : 9,"seconds" : 55,"time" : 1476113995244,"timezoneOffset" : -330,"year" : 116
},"customerId" : "npsd3Ldfsdf1x0hsdfsdf2mj14VUA876f2","id" : "20161010210955","status" : "FX_FULL"
} }
解决方法
你为什么不先检查状态？你知道开始状态的价值.我认为这个解决方案应该是最佳方式.
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if("FX_OVER".equals(dataSnapshot.getValue(String.class)) {
reference.getParent().addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot parent) {
// This is a defensive check. I dont know this is necessary.
// If status exist,parent must be exist.
if (parent.exists()) {
Order newOrder = parent.getValue(Order.class);
if (newOrder != null) {
processOrder(newOrder);
}
}
}
@Override
public void onCancelled(DatabaseError databaseError) {}
});
}
}
@Override
public void onCancelled(DatabaseError databaseError) {}
});
