The Write Method

Go Up to Access Methods (properties)

The write method for a property is a procedure that takes a single parameter (except as noted below) of the same type as the property. The parameter can be passed by reference or by value, and can have any name you choose. By convention, the write method's name is Set followed by the name of the property. For example, the write method for a property called Count would be SetCount. The value passed in the parameter becomes the new value of the property; the write method must perform any manipulation needed to put the appropriate data in the property's internal storage.

The only exceptions to the single-parameter rule are for array properties and properties that use index specifiers, both of which pass their index values as a second parameter. (Use index specifiers to create a single write method that is shared by several properties. For more information about index specifiers, see the Delphi Language Guide Index.)

If you do not declare a write method, the property is read-only.

Write methods commonly test whether a new value differs from the current value before changing the property. For example, here is a simple write method for an integer property called Count that stores its current value in a field called FCount:

procedure TMyComponent.SetCount(Value: Integer);
begin
  if Value <> FCount then
  begin
    FCount := Value;
    Update;
  end;
end;

void __fastcall TMyComponent::SetCount( int Value )
{
  if ( Value != FCount )
  {
    FCount = Value;
    Update();
  }
}