问题
FirebaseDatabase.getInstance().getReference("Block").addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot snap : dataSnapshot.getChildren()) {
if(snap.getKey().equals(myUID)){
FirebaseDatabase.getInstance().getReference("Block").child(myUID).addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot snap : dataSnapshot.getChildren()) {
if(snap.getKey().equals(list.get(position).getUid())){
FirebaseDatabase.getInstance().getReference("Block").child(myUID).child(list.get(position).getUid()).addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot snap : dataSnapshot.getChildren()) {
if(snap.getValue().equals("1")){
call_method();
}else{
//code...
}
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
} else {
call_method();
}
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
} else {
call_method();
}
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
This code works well, but it is very long so I am asking for the best way to write it ?
I want to check firstly if Block node has child equals to my UID if it is true then I want to check if my UID has child equals to specific UID if it is true then I want to get the value of block which is 0 in this example
How can I do that ? Thank you very much.
回答1:
Just traverse to the path specified using child. You will get no data if the path doesn't exist.
FirebaseDatabase.getInstance().getReference("Block")
.child("MyUUID")
.child("specificUUID")
.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(dataSnapshot.exists()) {
// ... Do something
} else {
call_method();
}
// ... Other code
}
回答2:
Try this:
Firebaseuser user=FirebaseAuth.getInstance().getCurrentUser();
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("Block");
ref.child(user.getUid()).addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(dataSnapshot.exist()){
//checks first uid
if(dataSnapshot.hasChild(seconduid){
//checks if seconduid is there
for(DataSnapshot datas:dataSnapshot.getChildren()){
String blocks=datas.child("block").getValue().toString();
}
}
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
This will check the first uid if(dataSnapshot.exist()) after that it will check if that uid node has the second uid that you provide if(dataSnapshot.hasChild(seconduid){ then you will iterate and get the node block
来源：https://stackoverflow.com/questions/49212932/what-is-the-best-way-to-check-the-existence-of-every-child-in-one-node