Delphi: Cannot perform this operation on a closed dataset (XE6) - sql

Question

I have a little piece of code that gets a corresponding value from database when one is entered, that is, in a database like this
Code Name
1 A
2 B
3 C
When you enter 1 in the code area, it returns A, and if you enter B in the Name area, it returns 2.
I can get this to work just fine with the following code but an error message would pop out showing "Cannot perform this operation on a closed dataset"
Does anyone know how to solve this problem? Any help would be appreciated. Thanks
procedure TStock_Bookkeeping.Stock_Code_ValueChange(Sender: TObject);
begin
Price_Per_Share_Value.Text := GetCurrentPrice(Stock_Code_Value.text);
ExecuteSQL_CodeToName(Stock_Code_Value.Text);
end;
procedure TStock_Bookkeeping.Stock_Name_ValueChange(Sender: TObject);
begin
ExecuteSQL_NametoCode(Stock_Name_Value.Text);
end;
procedure TStock_Bookkeeping.ExecuteSQL_CodeToName(const inCode: string);
var
query : TFDQuery;
begin
query := TFDQuery.Create(nil);
try
ConnectToSQLite;
query.Connection := FDConnection1;
query.SQL.Text := 'SELECT * FROM Code_Name where Code =' + '"' + inCode + '"' ;
query.Active := True;
query.Open();
while not query.Eof do
begin
Stock_Name_Value.text := query.FieldByName('Name').AsString;
query.Next;
end;
finally
query.Close;
query.DisposeOf;
end;
end;
procedure TStock_Bookkeeping.ExecuteSQL_NameToCode(const inName: string);
var
query : TFDQuery;
memTable : TFDMemtable;
begin
query := TFDQuery.Create(nil);
try
ConnectToSQLite;
query.Connection := FDConnection1;
query.SQL.Text := 'SELECT * FROM Code_Name where Name ='+'"'+ inName+'"';
query.Active := True;
query.Open();
while not query.Eof do
begin
Stock_Code_Value.text := query.FieldByName('Code').AsString;
query.Next;
end;
finally
query.Close;
query.DisposeOf;
end;
end;

Answer 1

Set a breakpoint and walk the code (F7):
If the Stock_Code_ValueChange event is connected to the Stock_Code_Value edit box when you change the value of Stock_Code_Value.Text you are changing the value of Stock_Name_Value.Text which then fires the Stock_Name_ValueChange event but you have not completed the Stock_Code_ValueChange event.
Add a Stock_Name_ValueOnChange := nil as the first line of the Stock_Code_ValueChange procedure and a Stock_Name_ValueOnChange := Stock_Name_ValueChange as the last line of the procedure to stop the Stock_Name_ValueChange event from firing while the Stock_Code_ValueChange event is processing.
Then do the opposite for the Stock_Name_ValueChange event.