Tutorial: Working with Multiple Forms

The objective of this tutorial is to learn how to create a multi-form application and to navigate between the forms at run time. At the end of this tutorial you should be able to:

Create applications consisting of more than one form.
Include in applications forms that have been created previously.
Provide simple code to enable users to navigate between forms at run time.

Adding new forms to an application

When VB is launched it provides a blank form called Form1. All but the most trivial programs consist of more than one form. For example, it is common to have a welcome screen offering a number of options and for each of these to branch to different forms. The high level structure of an interactive application can often be understood best from a diagram showing the forms hierarchy. Imagine a computer-based learning package containing a number of modules, each of which has a number of forms associated with it.

To add a new (blank) form to an application, select New Form from the File menu. This form can now be designed and coded in the same way as the first form.
To include an existing form (one already created and saved on C: drive or diskette) in an application, select Add File from the File menu. Remember that VB keeps only one copy of each file (even if it is used in different applications) so if you want to use and modify an existing file, you must save it with the Save As option.

To move between forms at run time you need to Hide the current form and Show the next one. This is done with the following statements where your own form names are substituted for X and Y. These statements should be attached to the event (e.g. button click) that causes the change of form to occur.

frmX.Hide frmY.Show

Note: The name of the form to be hidden or shown is the ‘internal’ name used by VB. This is the name displayed in the right hand column of the Project window and is the nane displayed for a form in the Properties window. Do not confuse this with the name of the form when it gets saved to disk, this name will have the extension .FRM.

Note: Every form which is displayed (shown) in Visual Basic is first loaded into memory and even when it is hidden it still remains loaded in memory. This is not a problem with two or three forms, but above this and you can run out of available memory. If this happens the solution is to discard some of the forms not required. Use the Unload command to do this:

Unload frmX

Conversely the Load command can be used to load a form into memory but without displaying it. It should also be noted that the command Show will automatically load a form if it is not already loaded, and the command Unload will automatically hide a form if it is not already hidden before being unloaded.

	frmX.Hide Unload frmX This is code will run perfectly but the first line is superfluous since VB automatically hides any visible forms before they are unloaded from memory
	Unload frmX frmX.Hide The form `frmX` will automatically be hidden and then unloaded from memory on line 1, then on line 2 the program wishes to hide the form. Because the form which is to be hidden is no longer in memory VB automatically loads it. Thus, the code in line 1 is counteracted.
	Unload frmX
	Load frmY frmY.Show This code will work perfectly but the first line is unnecessary since VB performs a load automatically if the form to be displayed is not already in memory. The only situation where `Load` should be used is if you wish to load a form into main memory, perform some other actions, and then later actually show the form.
	frmY.Show

Task

Just to get the idea of creating multi-form applications quickly, create a master program to contain several of the tutorial exercises completed already.

Start a new project. The first form should be a welcome screen (called frmWelcome), use graphical techniques to make it look attractive. Include on the form three command buttons with appropriate pictures on them to represent the applications you want to include (perhaps the language tutor, restaurant program and animation program). Add a Quit button to terminate the program.

Using the Add File option, load the forms for these applications into your project. The forms will have to have unique names before you load them - hopefully they have been named sensibly and are not all called Form1!

Code the command buttons on the welcome screen to hide that screen and show the appropriate next one.

If the subsequent screens have Quit buttons, change the captions on these and program them to return to the welcome screen. If not, add new buttons to perform this function.

If public variables have been used you will need to preserve these in a shared Module1.bas, resolving any duplicate names.

Screen hierarchy

See if you can work out how to return the program automatically to the welcome screen if there is no interaction from the user for one minute. Hint: You will need to use the Timer control , the MouseMove event and a global variable to act as a ‘clock’. Please read Timing events in Visual Basic or use VB’s online help to find out how the Timer works.

Tutorial 8 (Animation and Graphics)

Tutorial 10 (Using the Grid Control)