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[英]How to retrieve all the data from a node in Android Firebase realtime database?
[英]how to retrieve profit of all mobiles from Firebase Realtime database and sum all the values
我正在創建一個銷售購買應用程序,我想檢索銷售手機的所有利潤並對這些值求和以獲得總收入。
mDatabaseReference.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
List<Float> list = new ArrayList<>();
for (DataSnapshot ds : dataSnapshot.getChildren()) {
list.add(Float.valueOf(Float.parseFloat(ds.child("profit").getValue().toString())));
double sum = 0.0;
for (Float d : list) {
double floatValue = (double) d.floatValue();
Double.isNaN(floatValue);
sum += floatValue;
}
Toast.makeText(RecordsActivity.this, "Earning = " + sum, Toast.LENGTH_SHORT).show();
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
Toast.makeText(RecordsActivity.this, databaseError.getMessage(), Toast.LENGTH_SHORT).show();
}
});
對於初學者,我建議您將利潤作為整數發送到數據庫。 然后您可以在數據快照中找到節點利潤下的數字總和,如下所示
@Override
public void onDataChange(@NonNull DataSnapshot
dataSnapshot) {
int sum=0;
for (DataSnapshot ds1:dataSnapshot.getChildren()){
int a=ds1.child("profit").getValue(Integer.class);
sum+=b;
int i = sum;
String value = String.valueOf(i);
Toast.makeText(RecordsActivity.this, value,
Toast .LENGTH_SHORT).show();
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
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