Hi Boris,

Based on my understanding, you'd like to validate the value of some custom
properties of your custom control before build starts. If I'm off base,
please feel free to let me know.

In fact, you needn't trap the build start event from designer to get what
you want. Instead, you could put the validating code in the set accessor of
the custom property.

The following is a sample:

public ref class MyControl: public System::Windows::Forms::UserControl
{
    private: System::String^ s;
    public :
    property System::String^ S
    {
        System::String ^ get()
        {
            return s;
        }
        void set(System::String ^ value)
        {
            if(value=="123")
            {
                throw gcnew Exception("invalid data");
            }
            s = value;
        }
    }
}

Build the project and add the custom control on your form. If you set the
value of the property S in the Properties window to "123", a dialog pops up
saying "Property value is not valid" and forces you to change the value.

Hope this helps.
If you have any question, please feel free to let me know.

Sincerely,
Linda Liu
Microsoft Online Community Support

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