Delphi : Setting OnGetText Event Handler for fields of a dynamic query

Question

I want to set my own procedure to OnGetText event of fields in a dynamic query

My procedure is like this :

procedure TMainFrm.MyFieldGetText(Sender: TField; var Text: String;
  DisplayText: Boolean);
begin

  ...

end;

"...Captions" are String array constants

I set the event handler in OnAfterOpen event of ADOQuery :

procedure TImportFrm.ADOQueryAfterOpen(DataSet: TDataSet);
var
 I : Integer;
begin
 for I := 0 to ADOQuery.FieldCount - 1 do
  ADOQuery.Fields[I].OnGetText := MainFrm.MyFieldGetText;
end;

But after opening ADOQuery , there is no Text to display , it looks like the Text value is empty !

It seems it doesn't matter what my procedure do , because when I set an empty procedure ( with no code ) , no text displayed too

what goes wrong ?

thanks ...

Check your handler with the Debugger (set a breakpoint at the first line) — mjn, Jul 29 '15 at 04:56
thanks , but as I say : "It seems it doesn't matter what my procedure do , because when I set an empty procedure ( with no code ) , no text displayed too" — Mahmoud_Mehri, Jul 29 '15 at 04:59
Do you want to check against Sender.FieldName instead of Sender.Name? — Jason, Jul 29 '15 at 05:01
Your concept is essentially correct. But your code is unsafe. Refer to `DataSet` and `Self` inside the `AfterOpen` event handler rather than to a component field and global form variable. Better write `for I := 0 to DataSet.FieldCount - 1 do DataSet.Fields[I].OnGetText := MyFieldGetText;`. — TLama, Jul 29 '15 at 06:24
Your conclusion is wrong. If you assign a procedure to OnGetText you are responsible for the value. Therefore if you assign an empty procedure nothing is displayed. So the problem might be in the procedure. — yonojoy, Jul 29 '15 at 08:36
You've not given much to go on. As @TLama says, the code looks fine (other than the points he raised). Run the debugger, check that i) the event fires at all, ii) what the text variable is set to after calling. Also try stepping through the rest of the source to see what happens to Text. — Matt Allwood, Jul 29 '15 at 08:37
@TLama : thanks , I tried this but the problem not solved. In fact , the procedure is assigned but the problem is after assigning the procedure , DBGrid shows nothing ! — Mahmoud_Mehri, Jul 29 '15 at 08:39
@Mahmood_M Do you, by any chance, remember what value does `Text` get after calling the procedure? If you do, you can add an answer [here](http://stackoverflow.com/questions/43913332) — Sнаđошƒаӽ, May 11 '17 at 11:03

Val Marinov · Accepted Answer · 2015-07-29T09:13:11.777

3

Try this:

procedure TMainFrm.MyFieldGetText(Sender: TField; var Text: String;
  DisplayText: Boolean);
begin
  if Sender.FieldName = 'XX' then
   begin
     Text := .... String(Sender.Value);// ( or Text := Sender.AsString);
   end;
  if Sender.FieldName = 'YY' then
   begin
     Text := .... String(Sender.Value);// ( or Text := Sender.AsString);
   end;
  ...

end;

edited Jul 29 '15 at 09:13

answered Jul 29 '15 at 08:39

Val Marinov

2,705
17
22

1

Why the branch for `FieldName` then ? You could directly write `Text := Sender.AsString;`. – TLama Jul 29 '15 at 08:42
@TLama Because OP wrote this before he had editted the question. – Val Marinov Jul 29 '15 at 08:49

Mahmoud_Mehri · Answer 2 · 2015-07-29T10:28:15.330

Thanks all

The problem was that I should mention all situations of Text and should use Sender.value instead of Text in right side ! , I changed my procedure to this and problem solved :

procedure TMainFrm.MyFieldGetText(Sender: TField; var Text: String;
  DisplayText: Boolean);
begin
 if Sender.AsVariant = Null then
  Exit;

 Text := Sender.AsString;

 if MatchStr(Sender.FieldName, BooleanFieldNames) then
  Text := BooleanCaptions[Sender.AsInteger];

 if Sender.FieldName = 'BNStatus' then
  Text := BNStatusCaptions[Sender.AsInteger];

 if MatchStr(Sender.FieldName, ['FStatus', 'LStatus', 'FirstStatus']) then
  Text := FLStatusCaptions[Sender.AsInteger];

 if Sender.FieldName = 'PayType' then
  Text := PayTypeCaptions[Sender.AsInteger];

 if Sender.FieldName = 'BGType' then
  Text := BGTypeCaptions[Sender.AsInteger];

 if Sender.FieldName = 'Updated' then
  Text := UpdatedCaptions[Sender.AsInteger];

 if Sender.FieldName = 'DieUser' then
  Text := DieUserCaptions[Sender.AsInteger];

 if Sender.FieldName = 'LiveUser' then
  Text := LiveUserCaptions[Sender.AsInteger];

 if Sender.FieldName = 'NVStatus' then
  Text := NVStatusCaptions[Sender.AsInteger];

 if Sender.FieldName = 'BSGender' then
  Text := BSGenderCaptions[Sender.AsInteger];

 if Sender.FieldName = 'BSMType' then
  Text := BSMTypeCaptions[Sender.AsInteger];

end;

Thanks again ...

You can use `Sender.AsInteger` instead of `StrToInt(Sender.Value)` if those fields are of integer type. — TLama, Jul 29 '15 at 10:12
yes , I have changed to this, and added " if Sender.AsVariant = Null then Exit;" for make code safer for empty values. — Mahmoud_Mehri, Jul 29 '15 at 10:26
For checking if the field is NULL you can use `Sender.IsNull`. — TLama, Jul 29 '15 at 12:14

Delphi : Setting OnGetText Event Handler for fields of a dynamic query

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