Ruud 0 Posted October 9 procedure TForm1.Form_Create (Sender: TObject); begin ComboBox1.ItemIndex := -1; ComboBox1.Text := 'ComboBox Test'; ComboBox1.Items.Clear; ComboBox1.Items.Add ('Test 0'); ComboBox1.Items.Add ('Test 1'); (...) end procedure TForm1.ComboBox1_Change (Sender: TObject); begin case ComboBox1.ItemIndex of 0 : ShowMessage ('Combobox1_Change | ItemIndex = 0'); 1 : ShowMessage ('Combobox1_Change | ItemIndex = 1'); end; end; procedure TForm1.Panel1_Click (Sender: TObject); begin ComboBox1.ItemIndex := 1; end; After starting the program , the ComboBox1 text is 'ComboBox Test' . When I select 'Test 0' in ComboBox1 , the ComboBox1 text is changed into 'Test 0' , and the correct message box (with message 'Combobox1_Change - ItemIndex = 0') is displayed . But when I click on Panel1 , only the ComboBox1 text is changed into 'Test 1' . There's no message box ! What extra statement must be added to the Panel1_Click procedure ? Share this post Link to post
corneliusdavid 212 Posted October 9 3 hours ago, Ruud said: But when I click on Panel1 , only the ComboBox1 text is changed into 'Test 1' . There's no message box ! The documentation for TComboBox.OnChange has this note: Quote Note: OnChange only occurs in response to user actions. Changing the Text property programmatically does not trigger an OnChange event. 3 hours ago, Ruud said: What extra statement must be added to the Panel1_Click procedure ? I'd extract the case statement from ComboBox1_Change to a separate procedure and call the new procedure from both ComboBox1_Change and Panel1_Click. Share this post Link to post
Ruud 0 Posted October 9 5 hours ago, corneliusdavid said: The documentation for TComboBox.OnChange has this note: Quote Note: OnChange only occurs in response to user actions. Changing the Text property programmatically does not trigger an OnChange event. Thanks for your response , but I did not change the Text property in the Panel1_Click . I changed the ComboBox1.ItemIndex property . Shouldn't that be enough to trigger the ComboBox1_Change ? Share this post Link to post
PeterBelow 238 Posted October 9 23 minutes ago, Ruud said: Thanks for your response , but I did not change the Text property in the Panel1_Click . I changed the ComboBox1.ItemIndex property . Shouldn't that be enough to trigger the ComboBox1_Change ? No, since it is not a user-triggered change from the combobox's view. Share this post Link to post
corneliusdavid 212 Posted October 9 4 hours ago, Ruud said: I did not change the Text property in the Panel1_Click . I changed the ComboBox1.ItemIndex property . You're right--sorry; still, like PeterBelow said, it's not a user-triggered change. Share this post Link to post
Ruud 0 Posted October 9 4 hours ago, PeterBelow said: No, since it is not a user-triggered change from the combobox's view. 10 minutes ago, corneliusdavid said: You're right--sorry; still, like PeterBelow said, it's not a user-triggered change. User-triggered ? But clicking on Panel1 did do something with ComboBox1 : visibly it changed the Text property from 'Test 0' to 'Test 1' (most likely because ItemIndex was changed from 0 to 1) . That information is only available in ComboBox1 . It looks like ComboBox1_Change is partially executed . I don't know why the case statement isn't executed as well . Share this post Link to post
Remy Lebeau 1385 Posted October 9 11 minutes ago, Ruud said: User-triggered ? The user did not interact with the ComboBox directly, they interacted with the Panel instead. The Panel's OnClick event invoked an API call to the ComboBox (the ItemIndex setter sends a CB_SETCURSEL message to the ComboBox), thus the text change is not a user-triggered action from the ComboBox's perspective, it is an application-triggered action. The ComboBox's OnChange event is fired in reply to a CBN_EDITCHANGE notification from the ComboBox, and CB_SETCURSEL does not trigger a CBN_EDITCHANGE notification. Share this post Link to post
Ruud 0 Posted October 9 (edited) 1 hour ago, Remy Lebeau said: The user did not interact with the ComboBox directly, they interacted with the Panel instead. The Panel's OnClick event invoked an API call to the ComboBox (the ItemIndex setter sends a CB_SETCURSEL message to the ComboBox), thus the text change is not a user-triggered action from the ComboBox's perspective, it is an application-triggered action. The ComboBox's OnChange event is fired in reply to a CBN_EDITCHANGE notification from the ComboBox, and CB_SETCURSEL does not trigger a CBN_EDITCHANGE notification. OK , thank you all , I'm convinced , it's not a user-triggered change . So , because Delphi won't execute the ComboBox1_Change event handler for me voluntarily , I'll force Delphi to do so ! procedure TForm1.Panel1_Click (Sender: TObject); begin ComboBox1.ItemIndex := 1; ComboBox1_Change (Sender); { <<==== } end; Problem solved ! Edited October 9 by Ruud Share this post Link to post
Brian 1 Posted October 12 type TComboboxHelper = class helper for TCombobox public procedure DoOnChange; end; implementation { TComboboxHelper } procedure TComboboxHelper.DoOnChange; begin if Assigned(OnChange) then Onchange(Self); end; I would put this to a helper to save me problems when I change the procedure on combobox OnChange. procedure TForm1.Panel1_Click (Sender: TObject); begin ComboBox1.ItemIndex := 1; ComboBox1.DoOnChange; end; 1 Share this post Link to post