Starting a new Delphi project generates and displays the first form in the project file. To view the project file code, from the IDE menu go to Project | View Source.

The line we are interested in is painted red:

program Project1;

uses
  Forms,
  Unit1 in 'Unit1.pas' {Form1};
{$R *.res}
begin
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

The method CreateForm prepares the form to be displayed as the program's main form. The form is not displayed until the next line executes:

Application.Run;

Executing CreateForm utilizes memory and system resources. This is not a problem with an application with a single form, but if the project has many forms and they are all created at program startup you may run into low resource problems down the road. Your development computer probably has plenty of memory installed but the situation may be quite different on users' machines, where your application has to run with much more limited resources and in competition with other applications.

The solution is simple: take control of form creation and destruction.

Taking Control

To add two new forms in the project, simply point to File | New | Form. This will create (and add) a new form named Form2 (+ Unit2) to the project. Rename this form (using the Object Inspector) to 'frmAddNewCustomer'. Repeat the steps for the third form, change the name to 'frmEditCustomer' (leave the name of the unit to be 'Unit3'). When you define the two subsidiary forms Delphi places the following code into the project file:

begin 
  Application.Initialize; 
  Application.CreateForm(TfrmMain, frmMain); 
  Application.CreateForm(TfrmAddNewCustomer, frmAddNewCustomer); 
  Application.CreateForm(TfrmEditCustomer, frmEditCustomer); 
  Application.Run; 
end

Each Application.CreateForm... line creates the form object specified by the variable in the second argument as an instance of the class specified in the first. If you leave the code as it is, all three forms will be created in order. The first form in the list (named frmMain here, but it could be any name) is designated as the main form for the project and will be visible once Application.Run has executed. To show either of the other forms you would to apply code to some user-generated event to "show" it (i.e. bring it to the top):

frmAddNewCustomer.Show; 
//or
frmAddNewCustomer.ShowModal;

Ok, so what are the diferences between the Show and ShowModal methods?

Next page > Displaying Modal forms > Page 1, 2, 3, 4