Custom Component: Combobox Property

Samuel Smith

Last one in this vein.

I have a custom component. I need to add in a property that is essentially a combobox: letting the user select from a list of items. This list isn't predetermined: it can expand or contract based on certain conditions.

Essentially, I want to display a TStringList, and know which one of the objects the user has selected.

How would I do this?

Samuel Smith

Alright, I'll write down what I've come up with. There's no real easy way to do this, and you have to write a custom property editor.

First, I made a custom property.

class CustomStringList : public TStringList
{
   typedef TStringList inherited;
  private:
  void __fastcall SetValue( UnicodeString Value )
    {
      [indent]SelectedItem = IndexOf( Value );[/indent]
     };
     UnicodeString __fastcall GEtStrValue()
    {
         if (SelectedItem >= 0 && SelectedItem < Count )
                 return Strings[SelectedItem];
          else
         return "";
    };
public:
   int SelectedItem;
   __property UnicodeString SelectedString = {read=GetValue, write=SetValue};
   __fastcall CustomSTringList() : TStringList {SelectedItem = -1;};

}

Then I had to make a custom property editor

class CustomStringListPropertyEditor : public TfrxPropertyEditor
{
  typedef TfrxPropertyEditor inherited;
  public:
    TfrxPropertyAttributes virtual __fastcall GetAttributes()
    {
      TfrxPropertyAttributes Results;
      Results << paReadOnly;
      Results << paValueList;
      return Results;
    };
    
    virtual void __fastcall GetValues()
    {
        // Fetch all the current available options.
        CustomStringList* SL = (CustomStringList*) GetOrdValue(); // The pointer is stored in the int value
        Values->Clear();
        Values->AddStrings( SL );
    };

    inline __fastcall virtual CustomStringListPropertyEditor( TfrxCusotmDesigner* Designer); TfrxPropertyEditor(Designer) {};
};

In the custom component I needed to use that class as a property in the published section

class CustomComponent : publicTfrxComponent
{
   private:
      CustomStringList* SL;
  __published
      __property CustomStringList* Combobox = {read=SL, write=SL};
};

And then, in the initialization of the component, you have to register the property editor (as well as the custom component)

....
(frxPropertyEditors())->Register( __delphirtti(CustomStringList), NULL, "", __classid(CustomStringListPropertyEditor));