More of this Feature • Page 1: Component references • Page 3: Binary properties • Page 4: Collections • Page 5: Sub-properties • Download Demo Projects

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   Sets
This section is really quite simple and will not take long to cover. I do not doubt that you are already familiar with creating your own ordinal types.

type
  TComponentOption = (coDrawLines,
                      coDrawSolid,
                      coDrawBackground);  

Properties of this type will show a combobox with a list of all possible values, but sometimes you will need to set a combination of many (or all) of these values. This is were sets come in to play

Type
  TComponentOption = (coDrawLines,
                      coDrawSolid,
                      coDrawBackground);  
  TComponentOptions = set of TComponentOption;

Publishing a property of type TComponentOptions would result in a [+] appearing next to our property name. When you click to expand the property you will see a list of options. For each element in TComponentOption you will see a Boolean property, you can include / exclude elements from your set by setting its value to True / False.

It is simple to check / alter elements in a set from within our component like so.

if coDrawLines in OurComponentOptions
  then DrawTheLines; 

or

procedure TsomeComponent.SetOurComponentOptions(const value : TComponentOptions);
begin
  if (coDrawSolid in Value) and
  (coDrawBackground in value) then
    {raise an exception}

  FOurComponentOptions := Value;
  Invalidate;
end;

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Creating Custom Delphi Components >>
>> Part III.