Typecasting

[dkeene]

Hello, all. 

If I create a new unigui component at runtime:

var

aNewUniComponent: TObject;

begin

   aNewUniComponent:=TUniDBMemo.Create(self);

   ... 

 

then I wish to associate it with a Data Field. I know it's a data-aware control, so I should be able to do the following:

   TUniDBEdit(aNewUniComponent).DataField:='aFieldName';

whether it's a TUniDBEdit, TUniDBMemo, TUniDBNumberEdit, etc.

This fails, however, with an access violation, although I am not sure why, and only works with the exact same class: 

   TUniDBMemo(aNewUniComponent).DataField:='aFieldName';

otherwise I may get an Invalid Pointer Operation error.

 

My Question is if there is a Class from which all data-aware unicontrols descend such that I can typecast without access violations, such as

   TUniDBControl(aNewUniComponent).DataField:='aFieldName';

Other wise I need to use a series of if then else statements like:

   if ClassName='TUniDBEdit' then

      TUniDBEdit(aNewComponent).DataField:='aFieldName' else

   if ClassName='TUniDBMemo' then

      TUniDBMemo(aNewComponent).DataField:='aFieldName' else

   if ClassName='TUniDBNumberEdit' then

      TUniDBNumberEdit(aNewComponent).DataField:='aFieldName' else

etc.

or perhaps there is a better way?
Thank you in advance

Doug

[x11]

may be
 

if assigned(aNewComponent) then
begin
  if aNewComponent is TUniDBEdit then 
  begin
    TUniDBEdit(aNewComponent).DataSource := ...;
	TUniDBEdit(aNewComponent).DataField := ...;
  end;

  if aNewComponent is TUniMemoEdit then 
    ...

end;
  

 

[dkeene]

Thank you x11. I am trying to avoid a giant list of "if aNewcomponent is TUniDBEdit else if aNewComponent is TUniDBNumberEdit .. else if aNewComponent is TUniDB...

there might be a way of saying TUniDBBaseControl(aNewComponent).Datafield...

Thanks

Doug

[x11]

look in the documentation where the "datafield" property appeared

http://www.unigui.com/doc/online_help/api/uniDBEdit_TUniDBEdit.html

[x11]

http://www.unigui.com/doc/online_help/api/!!MEMBERTYPE_Properties_uniDBEdit_TUniCustomDBEdit.html

typecast to TUniCustomDBEdit

[x11]

another solition: check propery

uses
  System.TypInfo;

function HasDataFieldProp(AControl: TControl): Boolean;
begin
  Result := IsPublishedProp(AControl, 'DataField');
end;

https://stackoverflow.com/questions/48584888/checking-if-component-has-a-text-property