CIS 338: VB.NET Components

1. CIS 338: VB.NET Components Dr. Ralph D. Westfall April, 2011

2. Components = Building Blocks • form is the fundamental VB.NET component • = interface between user and other code • parts of a form • control box (click or double-click upper left corner) • Text (title) property • title bar • small buttons: minimize, maximize, close • follow along on laptops

3. Form Methods • if only one form, shows at Startup • can stop it by clicking small Close (x) button at top right, or run Close in code • do NOT use [frmName].Hide with only one form! • [frmName.]Close closes form, and also shuts down the project if there is only one form • End shuts down the project if there is more than one form

4. Controls • visible objects on forms or elsewhere • built into Visual Basic.NET or available from 3rd parties • examples of built in form controls • Button, TextBox, Label, CheckBox, RadioButtons, ListBox, ComboBox, etc. (view names on Visual Studio.NET Toolbox buttons)

5. Commonly Used VB.NET Controls • Label – puts text on a form • TextBox – accepts inputs, displays outputs • (Command) Button – causes code to run • CheckBox – accepts Yes/No inputs • (Option) RadioButtons – selects only one from multiple choices • ListBox – select from a list of choices • ComboBox – select from list or enter value

6. Sample Properties of Controls • properties = variables e.g., • (Name) of form or control • Location.X .Y = # of pixels from left and top edges of “container” • sets position on screen • container = what item is inside • a form is the container for Button, etc. • Size: Width Height are also in pixels • Anchor – attaches to side(s) of the form

7. Sample Properties of Controls - 2 • more properties • Enabled – True means user can change • for a Text Box that shows a calculated output, set Enabled = False (or show output in a Label instead) • Visible = True (or False) • guess what this does • where use? why? 'code

8. Using Properties of Controls • can set during development (“design time”) • can also use code to change (“run time”) • example: disable a Go to Next Form button until after user has entered inputs and clicked Enter button • use “dot notation” to reference properties • txtPayment.Text = CStr(decPayment) decPayment = CDec(txtPayment.Text) • conversions needed with Option Strict On

9. Some Label Control Properties • can set in Properties window or in code • AutoSize – label’s “box” expands to fit text • Font – size (points), font (typeface), style (bold, italic, etc.) • ForeColor – text color • BackColor – background color (behind text) • can use a white background color to make Label look like a TextBox (but why?)

10. Some TextBox Control Properties • setting content value (default) • txtName.Text = "Bubba" • for handling larger quantities of text • MultiLine – True enables text wrapping • goes to next line when reaches right side • ScrollBars determines if a scroll bar is used on a text box, and what type(s) • (None | Horizontal | Vertical | Both)

11. (Command) Button Properties • can use & in Text property to set shortcut key • [Alt] e runs &Exit, [Alt] r runs G&rin • may see an underline if & is before a letter in the middle of the word e.g., Grin • Enabled • if =True button is usable, but not if =False • when would you set it =False?

12. CheckBox Properties • 2 possible Checked (Boolean) Values: • False (not checked) • True (checked) • 3 possible CheckState Properties: • Unchecked • Indeterminate (checked and grayed; try it) • Checked

13. (Option) RadioButtons • only one radio button at a time can be selected • clicking one "unclicks" the other • different than clicking 2+ checkboxes • can use a GroupBox (container) to set up separate groups of radio buttons • user can only select one from each group

14. (Option) RadioButtons - 2 • Checked property is either True or False • two ways to run (checkboxes also) • can use [name]_Click method to cause code to run as soon as user clicks one • can use If … Then … Else or a Select Case structure to test a user choice later, instead of triggering an immediate action

15. GroupBoxes (are Containers) • can put other controls in a GroupBox • need to 1st put GroupBox on form, then put controls into it • GroupBox will notinclude controls already on form, even if you put it over them • can change appearance • Text – present or absent • FlatStyle – Standard, Popup, or System • ForeColor, BackColor, BackGroundImage

16. ListBoxes • 2 different kinds of ListBox • ListBox: selection is highlighted • CheckedListBox: selection is checked • lst[name].SelectedIndex property • item number of selected item in list (zero-based, starts at 0, but is -1 if unselected) • lst[name].Items.Count property (2 dots) • total number of items in ListBox 'code

17. Other List Box Properties • can use Sorted = True to sort, but this only sorts by left side of list if leftmost characters are the same • numbers are handled as text characters (lexical sort), so don't sort correctly e.g., 119 1-9 (or a-9) 5649 2-64 (or b-64, etc.) 94 3-119 9 4-5649 'prefix gives order 'or use leading zeros (0009, 0064 …)

18. ListBox Multiple Selection • 0, 1, or many based on SelectionMode • works on ListBox, not on CheckedListBox • 0 None – disabled • 1 One – can select only one item • 2 MultiSimple – can select with mouse, or arrow key followed by spacebar • 3 MultiExtended – also use Shift, Ctrl keys • if no item is selected, then SelectedIndex value is -1 regardless of SelectionMode

19. ListBox Multiple Selection - 2 • total number of selected items = lst[name].SelectedItems.Count • VB.NET creates a collection of specific selected items • can cycle through in a for loop e.g., For Each item inListBox1.SelectedItems MsgBox(item) Next

20. ListBox Properties that Are Useable in Code • .SelectedItem property shows user's 1st selected item (simple approach) str[variable] = lst[name].SelectedItem • .SelectedIndex property shows the sequential identifier of selected item • collection of items in the ListBox • (1st) selected item # is lst[name].ListIndex • lst[name].Items(lst[name].ListIndex)

21. Programmable List Box Properties - 2 • can set default selection in code with SelectedIndex property • 1st item in ListBox has SelectedIndex of 0 • 2nd item has 1 • SelectedIndex of -1 means that none is selected lst[name].SelectedIndex = 2 'which item? • can't set this in Properties window

22. ListBox & Collection Together

23. Adding Items to ListBox • using Items editor via Properties window • type in items, then click OK • can also paste into the editor window • programmatically lst[name].Items.Add("CIS") lst[name].Items.Add(str[variable]) • can load values into a parallel ArrayList (unlike an array, don't need to use a counter) als[name].Add(191919) 'code

24. ComboBox • like a combination (combo) of a TextBox and a ListBox • user can type information into the TextBox part to either enter an item not in the list or scroll down to item(s) in the (Sorted = True) list that start with the same letters • properties and methods are usually same or similar to those of a ListBox

25. ComboBox Properties • DropDownStyle property • 0 Simple (TextBox on top of a ListBox) • can select an item or type in something not in the ListBox part (Prof. Westfall's FAVORITE!!) • 1 Dropdown (ListBox drops down on a click) • can type in an item or initial letter(s), but don't see any match from the ListBox until it drops down • 2 DropdownList (ListBox drops down on click) • can't type anything in the TextBox part, but must click to drop down the ListBox to select an item

26. ComboBox Properties - 2 • Text property (for Styles Simple or DropDown) • can set it as a default selection, or make it be an instruction to the user when it runs, or leave it blank • code can access .Text property to get user inputs that are not in the list(box)

27. ComboBox Properties - 3 • can add objects to a ComboBox and make one attribute the DisplayItem • can then access other attributes of selected item • e.g., select name, get Social Security # 'code

28. Controlling Tab Sequence • if a control's TabStop property = True, user can use tab key to move from one control to the next • sequence is initially determined by order that item was added to form • set TabStop = False for items that will not be used for input (e.g. a Label or a TextBox or ListBox that displays outputs)

29. Changing Tab Sequence • can change by changing TabIndex • use a large number to make an item last • VB 6 changed tab indices to compensate for other changes • Visual Basic.NET seems to keep track of this in another way • tutorial (click Types of Windows>Tab Order) • set TabStop=True for Radio Buttons

30. Clicking to Change Tab Stops • in VB.NET, can mouse click items to change their tab sequence • View>Tab Order • then click each item in the order that you want for the tab sequence • repeated clicks on same item cycles through the TabIndex values • then click View>Tab Order (toggle it off) to set new values

31. Clicking to Change Tab Stops - 2 • note that Labels have a TabIndex property too, but not a TabStop property • so can't tab to them • could click them repeatedly to set all the values to 0, but not necessary • note that tab values in View>Tab Order don't match with TabIndex properties

32. Clearing Common Controls • sometimes need to clear (remove contents) of a control • txtName.Text = Nothing or txtName = "" • chkComputerOwner.Checked = False • rdoCategory.Checked = False • lstPersons.ClearSelected() • cboCities.SelectedItem = Nothing

33. Design Tips for Controls • hold down left mouse button and use cursor to select multiple controls • or hold Ctrl key and click items • after multiple items are selected, can move them as a group • can change properties of all selected controls by changing in one control • e.g., Font on Labels, Format>Align

34. Visual Studio's Format Menu • horizontal or vertical spacing • increase/decrease, make equal, remove • make same size • size to grid (all corners on grid points) • alignment • tops, lefts, etc.

35. Showing Grid Lines on Form • it can be helpful in designing a form to have grid lines showing during design • Tools>Options>Windows Forms Designer>General>Layout Settings>click Show Grid option • SnapToGrid LayoutMode forces controls to space themselves based on grid

36. Exercise • put a Button on a Form, and several other input controls covered today • click the Button, write code to put the keyboard inputs from one control into a different kind of control that takes Text • test, and then repeat with another pair of controls