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C++Builder Extensions to C++
value is loaded again from the form file when the form is loaded in the Form Designer, or
when the form is displayed in the application. By default all properties in the __published
section of the class declaration will be stored automatically. Properties that are contained in
the public section of a component’s class declaration are not automatically stored. To
specifically store a property, you set the stored property to true:
__property int Value { read=FValue, write=SetValue, stored=true };
As I said, all properties in the __published section of the class declaration will be stored
automatically. This is almost always what you want, so you may never have to use the stored
specifier for your published properties. But if, for some reason, you want to specifically
preclude a property from being stored, you can specify a value of false for the stored
specifier:
__property int Value { read=FValue, write=SetValue, stored=false };
Most of the time you can allow C++Builder to use the default storage action for your
properties.
Extending Base Class Properties
It is common to extend a property that is provided in the base class of the component you
have created. One of the most common reasons to do so is to change the default value of the
property. For instance, let’s say you had derived a new component from the TLabel
component and that this new component needed to have its text centered. In that case you
could redeclare the Alignment property as follows:
__property Alignment = { default=taCenter };
When your new component is placed on a form in the Form Designer, the Alignment
property will now default to taCenter. Note that you only need to add whatever specifiers
are needed to change the property. In this example the default specifier is the only one that
is changed, so it is the only one listed.
Another common need is to override the default behavior of a component when a particular
property is written to. In that case you could redeclare the property and just change the write
specifier:
__property Alignment = { write=MyWriteAlignment };
When you redeclare a published property, be sure that you place the redeclaration in the
__published section of the class declaration.
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