MultiForm Applications

1
Topics

• Multi-Form Applications
• Application Form Management
• When the Application Ends
• Opening Another Form and Returning
• Communicating Between Forms
• Dialogs

2
Multi-Form Applications

• Most applications require multiple forms
• More than one task performed under the
  application umbrella
• Multi-step tasks
• Too much information to fit on a single form
• The user should almost never be able to switch
  between different concurrently open windows

3
Multi-Form Applications

• You must take careful control over forms
• What the user sees
• When the application ends
• Which form opens first
• Which forms are open at any particular time
• Which forms are open and visible
• Which forms are open and invisible
• You need to avoid leaving an application running
  but with no visible forms

4
Things You Need to Know

• How to create a new form
• How to change the startup form for a project
• How closing forms can end the program
• How closing forms can leave a program running
  with no visible form
• How to set values on one form from another one
• How to create an object variable referencing a
  form and use it to open and communicate with a
  form
• How to use Dialog Boxes and predefined form types

5
Planning the Projects Navigation

• Top-Down menu navigation
• All other forms are reachedfrom the main menu
• Navigation always returns tothe main menu
• May have subordinate levels of menu
• Consider only letting top level menu end the
  application
• Other forms will Close
• Return to the top menu

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Planning the Projects Navigation (cont.)

• Multi-step task requires navigating through a
  sequenceof forms
• Return to top level menu from adifferent form
  than the one directlyreached

7
Planning the Projects Navigation (cont.)

• Multiple Paths
• Some forms may be reachedfrom different forms

8
Planning the Projects Navigation (cont.)

• The navigation approaches needed have
  implications for how you open and close forms
• Some needs may have multiple techniques
• Some techniques may not be suitable for some
  navigation needs

9
Form File Names

• When a new project is created it will
  automatically get a form called Form1 with a file
  name of Form1.vb
• The only way to take control of the forms file
  name is to delete the default form and create a
  new one
• Set the new forms name when it is created
• This will also be the file name
• Change the Project Startup Form
• Choose Project Properties from the menu

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Adding a New Form
1
2

• Add a new form in the Solution Explorer
• Right-click the project
• Select Add
• Select Windows Form
• Set the forms name andfile name in the
  resulting dialog
• (If the application is largeenough you should
  use folders to organize it)

3
11
Project Properties

• Use the Project Properties menu to set
  project form properties
• Start up form
• Always set this if youremove Form1 asfirst form
• Shutdown mode
• Determines when form closing ends
  theapplication
• I recommend When Last Form Closes choice

12
Showing a Form

• Three techniques to make a form visible
• FormName.Show
• Any code in the procedure following this
  statement will continue to execute
• User can click on either form
• FormName.ShowDialog
• Execution of code in the current procedure is
  paused until the called form is closed
• User cannot address any other form
• FromName.Visible True (do not use)

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Navigation Techniques

• You should almost never have more than one form
  active and available to the user at a time
• If Form A calls Form B you can make Form A
  unavailable in four ways
• Close Form A (FormA.Close)
• Make Form A invisible (FormA.Visible False)
• Disable Form A (FormA.Enabled False)
• Show Form B modally in dialog
  formFormB.ShowDialog
• Approaches 1 2 hide Form A while 3 4 leave
  Form A visible but unavailable

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Navigation Techniques (cont.)

• If you close the last open form you will end the
  application
• If you set a calling form (Form A) to be
  invisible or disabled and you close Form B
• You can leave the application running but with no
  visible form for the user to navigate from
• User must use Task Manager to end a compiled
  program
• Or stop debugging in development mode

15
Two Ways to Address a Form in Code

• (A) Refer to the form by its name
• May refer to any public property or method of the
  form using FormName.PublicPropertyOrMethod
• FormName.lblCustomerID.Text
• FormName.Show
• FormName.Text
• Any changes made to a property or value this way
• Persist as long as the application is running
• (unless explicitly changed elsewhere)

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Two Ways to Address a Form in Code (cont.)

• (B) Create an object variable instance of the
  form
• The copy of the form created in the variable
  (theFormName in the example above) only lasts as
  long as the variable is in existence
• Follows normal variable scoping rules
• Any settings made to the copy expire when the
  object variable expires
• New copies will revert to the forms definition
  from design view

Dim theFormName as New FormName theFormName.lblCus
tomerID.Text theFormName.Show
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Passing Values Between Forms

• Forms expose certain elements to code on other
  forms or in other classes or modules
• All controls
• Because controls are declared in the form
  designer scoped with Friend
• Any variable or custom-written property declared
  with
• Public
• Available to any code
• Friend
• Available to any code in the same project

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Passing Values Between Forms (cont.)
Public Class FormB Friend intCustomerID as
Integer

• If the declaration above exists on Form B code on
  Form A can address intCustomerID directly
• Any code on Form B can then read this value
• Common to read the value in the Form Load event
  but it can be read anywhere
• Code on other forms can also read the value
• Friend cannot be used in a procedure

Code on Form A FormB.intCustomerID
Convert.ToInt32(txtCustID.Text)
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Passing Values Between Forms (cont.)

• Any form or control property on any form can be
  set or read by code on another form
• FormName.PropertyName
• FormName.ControlName.PropertyName
• We can also write Friend scoped custom properties
  for forms
• Covered in the Object Oriented classes later in
  the semester

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Returning to The Correct Form

• In a straight hierarchical navigation structure
  managing return to the correct form is
  straightforward
• Form A can use FormB.ShowDialog to show Form B
• Focus will be returned to Form A when Form B is
  released
• Or Form B can explicitly show Form A because it
  is the only form that will ever open Form B

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Returning to the Correct Form (cont.)

• If both Form A and Form B (or any other form)
  both open Form C (Special Technique)
• On Form C put this code

Public Class FormC Friend theCallingForm As
Form Private Sub btnClose_Click...
theCallingForm.Show() Me.Close() End
Sub End Class
Note object declared as type Form
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Returning to the Correct Form (cont.)

• Flexible form navigation (cont.)
• On the calling form use this code
• Form C now has a reference to the form that
  called it
• Note that you cannot CLOSE the calling form or
  the called form will have no form reference

Public Class FormA/FormB Private Sub
btnFormC_Click... Dim theFormC As New FormC
theFormC.theCallingForm Me theFormC.Show()
Me.Visible False End Sub
Do not close the callingform
23
Dialogs

• VB comes with a rich collection of dialogs with
  which to create
• Interactive mini-forms
• Input box
• Message box

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DialogsMessage Boxes

• Message Boxes return a value indicating which
  button was pushed
• Button combinations
• AbortRetryIgnore
• OK
• OKCancel
• RetryCancel
• YesNo
• YesNoCancel

• Return Values
• 1 OK
• 2 Cancel
• 3 Abort
• 4 Retry
• 5 Ignore
• 6 Yes
• 7 No

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DialogsMessage Boxes (cont.)

• Message boxes can be called as a statement or
  used in a function format to return a value
• Experiment with the wide variety of icons
• Avoid using message boxes excessively

lblMessageBoxResult.Text MessageBox.Show("Sho
w the message", _ "Click the Buttons", _
MessageBoxButtons.RetryCancel, MessageBoxIcon.Ques
tion, _ MessageBoxDefaultButton.Button1)
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DialogsInput Boxes

• An input box displays afixed size mini form
  withOK and Cancel buttonsand a single text
  input area
• Returns the contents of the text area if the OK
  button is pressed
• Returns an empty string
• If the Cancel button is pressed
• If the text input area is empty

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Miscelaneous

• Remember to always Open the next form before
  closing the current form
• If the project is set to end after the last form
  closes you could inadvertently end the program
• Avoid situations where you are leaving open forms
  behind you
• Use Close or Menu to indicate this form will
  close but you will return to a higher form
• Use Exit to indicate that the program will end
• It is good practice to have only one place to end
  the program