How to: Access Design-Time Support in Windows Forms
Your custom components and controls are designable, which means they have settings that users can configure with a graphical user interface (UI) at design time. These settings usually affect instances of the component at run time.
If your class implements the IComponent interface, it can participate in a design environment like Visual Studio.
To access the design-time support provided by the .NET Framework, you need to complete the following steps.
You must add a reference to the design-time assembly, System.Design.dll. This assembly is not included in the .NET Framework 4 Client Profile. To add a reference to System.Design.dll, you must change the project's Target Framework to .NET Framework 4.
To access design-time support
Add a reference to the System.Design assembly.
If you are implementing a custom design-time experience for your component, import the System.ComponentModel.Design namespace.
If you are implementing a custom design-time experience for your Windows Forms control, import the System.Windows.Forms.Design namespace. You can create smart tags or a custom designer for your component with types in this namespace.