WORKING WITH MULTIPLE FORMS 67

Working with Multiple Projects

As you have noticed, every new project you create with VB is a so-called solution. Each solution contains a project, which in turn contains one or more files, references to .NET or custom components, and other types of items, which will be discussed in the following chapters. Both solutions and projects are containers—they contain other items. A solution may contain multiple projects. Each project in a solution is independent of the other projects, and you can distribute the projects in a solution separately. So, why create a solution? Let’s say you’re working on several related projects, which are likely to use common components. Instead of creating a different solution for each project, you can create a single solution to contain all the related projects.

Let’s build a solution with two related projects. The two related projects are the two calculators we built earlier in this chapter. The two projects don’t share any common components, but they’re good enough for a demonstration, and you will see how VB handles the components of

a solution.

VB.NET at Work: The Calculators Solution

Create an Empty Project and name it Calculators by selecting File New Blank Solution. In the Solution Explorer window, you will see the name of the project and nothing else, not even the list of references that are present in any other project type. To add a project to the solution, choose File Add Project Existing Project. (You can also right-click the solution’s name in the Solution Explorer, select Add Existing Item Project, and, in the dialog box that pops up, select the Calculator project.) Do the same for the LoanCalculator project. When the Add Existing Project dialog box appears, navigate to the folders with the corresponding projects and select the project’s file.

You now have a solution, called Calculators, that contains two projects. If you attempt to run the project, the IDE doesn’t know which of the two projects to execute and will generate an error message. We must decide how to start the new project (that is, which form to display when the user runs the Calculators application). When a solution contains more than a single project, you must specify the startup project. Right-click the name of one of the projects and, from the context menu, select Set As StartUp Project. To test a different project, set a different StartUp project. Normally, you will work for a while with the same project, so switching from one project to another isn’t really a problem. It is also possible that different developers will work on different projects belonging to the same solution.

Let’s say you’re going to design a documentation file for both projects. A good choice for a short documentation file is an HTML file. To add an HTML file to the solution, right-click the solution’s name and select Add New Item. In the dialog box, select the HTML Page template, and then enter a name for the new item. An HTML page will be added to the project, and an empty page will appear in the Designer. This is the newly added HTML page, and you must add some content to it.

Place the cursor on the design surface and start typing. Figure 2.13 shows a very simple HTML page with an introduction to the application. To format the text, use the buttons on the toolbar. These buttons embed the appropriate tags in the text, while you see the page as it would appear in the browser. This is the Design view of the document. You can switch to the HTML view and edit the document manually, if you’re familiar with HTML. The HTML page can be used by either project—at the very least, you can distribute it with the application.

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68	Chapter 2 VISUAL BASIC PROJECTS

Figure 2.13

Adding an HTML Document to a solution

If you open the folder created for the project, you’ll find that it contains an unusually small number of files. The projects reside in their respective folders. Make a change to one of the project’s files. You can change the background color of the three TextBox controls on the LoanForm to a light shade, like Bisque. Then open the LoanCalculator project, and you will see that the changes have taken effect. VB doesn’t create new copies of the forms (or any other component) added to the Calculators solution. It uses the existing files and modifies them, if needed, in their original locations. Of course, you can create a solution from scratch and place all the items in the same folder. Each project is a separate entity, and you can create executables for each project and distribute them.

To create the executables, open the Build menu and select Build Solution or Rebuild Solution. The Build Solution command compiles the files that have been changed since the last build; Rebuild Solution compiles all the files in the project. The executables will be created in the Bin folder

under each project’s folder. The file Loan.exe will be created under the \Loan\Bin folder and the

Calculator.exe file under the \Calculator\Bin folder.

The solution is a convenience for the programmer. When you work on a large project that involves several related applications, you can put them all in a solution and work with one project at a time. Other developers may be working with other projects belonging to the same solution. A designer may create graphics for the applications, you can include them in the solution, and they’ll be available to all the projects belonging to the solution.

The Calculators project we built earlier contains copies of the forms we added to the project. The Calculators solution contains references to external projects.

Executable Files

So far, you have been executing applications within Visual Basic’s environment. However, you can’t expect the users of your application to have Visual Studio installed on their systems. If you develop an interesting application, you won’t feel like giving away the code of the application (the source code, as it’s called). Applications are distributed as executable files, along with their support files. The users of the application can’t see your source code, and your application can’t be modified or made to look like someone else’s application (that doesn’t mean it can’t be copied, of course).

Note An executable file is a binary file that contains instructions only the machine can understand and execute. The commands stored in the executable file are known as machine language.

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