You are part of a development team building several ASP.NET applications for your organization. You want to create a reusable toolbar that will appear at the top of every page in each application, with its contents varying based on options the user selects when creating a profile. You also want the toolbar to be a reusable control that your team can add to the Visual Studio toolbox and drop onto pages in multiple projects. What should you do?

Introduction / Context:
ASP.NET provides two main approaches for creating reusable UI elements: Web user controls (.ascx) and Web custom server controls. User controls are easy to create but are typically reused within a single application. Custom server controls, especially when built in a Web Control Library, can be compiled into a shared assembly, added to the Visual Studio toolbox, and reused across multiple projects by different developers on the team.

Given Data / Assumptions:

• You are building several ASP.NET applications, not just one.
• You want a toolbar that can appear at the top of every page in each application.
• The content of the toolbar depends on user profile settings.
• You want the toolbar to be a reusable component that all developers can add to the Visual Studio toolbox.
• You prefer a solution that is easy to distribute and maintain across projects.

Concept / Approach:
A Web Control Library project compiles custom server controls into a DLL. These controls can then be referenced by any ASP.NET Web application, registered in web.config or at the page level, and appear in the Visual Studio toolbox. This is ideal for components that need to be reused across multiple applications. While Web user controls (.ascx) are convenient, they are file based, usually tied to a single Web project, and are not as easily shared or toolbox friendly as compiled custom controls.

Step-by-Step Solution:
1. In Visual Studio, create a new Web Control Library project that will contain custom server controls. 2. Add a new custom control class that inherits from System.Web.UI.WebControls.WebControl or a related base class. 3. Implement the toolbar's rendering and behavior, including logic that varies the toolbar contents based on the current user's profile settings. 4. Build the project to produce a DLL assembly containing your custom toolbar control. 5. Add a reference to this assembly in each ASP.NET application and configure Visual Studio so that the control appears in the toolbox, allowing developers to drag and drop the toolbar onto pages.

Verification / Alternative check:
After compiling the Web Control Library, you can right click on the Visual Studio toolbox, choose "Choose Items," and browse to the compiled assembly. The custom toolbar control will appear as a toolbox item, confirming that the design meets the requirement of being easily reusable and toolbox friendly. In contrast, a simple user control in a single Web project does not automatically appear in other projects without copying files manually.

Why Other Options Are Wrong:
Option b (user control) creates a reusable component but typically within one application; sharing it across multiple projects requires copying the .ascx file and associated code, and it is less straightforward to make it a toolbox item across solutions. Option c is incorrect because renaming an .aspx page to .ascx is not the correct way to create user controls and does not address cross project reuse. Option d, adding a generic component class, does not provide an ASP.NET UI control that can be rendered on pages; it is more suited for non visual components.

Common Pitfalls:
Developers sometimes start with user controls for everything and later struggle to share them between applications. Another pitfall is overlooking the benefits of versioning and distribution that come with compiled control libraries. When many applications rely on the same toolbar, maintaining it as a custom server control in a shared assembly simplifies updates and ensures consistency across the organization.

Final Answer:
You should create a new Web Control Library project and implement the toolbar as a Web custom server control so that it can be compiled into a DLL and added to the Visual Studio toolbox for reuse in all your ASP.NET applications.