VB Controls

 

Each control has Properties, Methods and Events.

 

1. Properties

Properties are what belong to the control, its data, its characteristics. When you assign a property value to a control it is actually a call of a Sub, not just a simple passive assignment. Eg: Changing Font or ForeColor, you see the result immediately.

Some properties can be assigned at Design time. Others can only be assigned at run-time, i.e. by coding.

You change Properties of a control at design time by using the Properties Window or the Properties Pages.

Some of the popular properties are:

 

Visible: If Visible = FALSE the control is invisible. So you can blink an object by alternating its visible property between True and False every 500 ms.

 

Enabled: If Enabled=False the object is grayed and does not respond to any mouseclick or keystroke. So to make a Commandbutton unavailable you set its Enabled property to False.

Example:

CmdSave.Enabled = False ‘ this greys the Save button

 

 

Properties Pages of a ToolBar

 

Left, Top, Width, Height: Left and Top are the X,Y coordinates of the control relative to its container (not necessarily its Form). Width and Height give the size of the control. An efficient way to change these values is by using the Move method .

Eg:

newX=100 : newY=50 : newWidth=3000 : newHeight=2000

MyControl.Move newX, newY, newWidth, newHeight

If you just want to move the form without changing its size then just leave the size data out:

MyControl.Move newX, newY

 

 

Sometimes you cannot find where a control is on its Form, locate it using the Properties Window (click the down arrow on the right of the combobox at the top of the Properties Window to see the list of all controls on the form.) then look at its Left and Top values. One of them may be too big or negative which places the control outside the form (i.e. out of view). Change that crazy value to bring the control back to earth.

 

TabIndex: As you press the Tab key, the cursor moves the focus of the Mouse/Keyboard Input from one control to the next. You define the order by which the cursor moves among the control by assigning a TabIndex value to each control. So if presently the cursor is on the control with TabIndex equal 3, when you next press the Tab key the cursor will move to the control whose TabIndex is 4. The cursor does not stop at a label, a control that is locked or a control whose TabStop value is False.

 

2. Methods

Methods are what the control can do. You ask the control to do something by itself when you call the control's method with some optional parameters.

Eg: The following code adds a line of text to Listbox List1

List1.Additem "This is the test line of text"

For example some of the methods of a Listbox are Clear, AddItem, RemoveItem

 

3. Events

Events are provided as available hooks for you to use. For example, you want to check the data entered

at a text box as soon as user finishes with it. In that case you can use the LostFocus event.

Example:

 

Sub TxtAge_Lostfocus()

If Val(txtAge.text) > 100 then

MsgBox "Warning: This person appears too old."

End if

End Sub

 

 

Click To write code for the Click event of a Commandbutton, doubleClick that button, VB will bring you to the Code window and position the editing cursor at the right place after generating the declaration of the Event Click Sub.

You can call the Sub ControlName_Click like a normal Sub because it does not require any parameters. This will emulate someone clicking the Control.

Eg:

Call CmdShowTime_Click

You can find out what events are available for a particular control by clicking the Combobox on the right in Code Window after selecting the control. Those events that have code are in bold, eg: Click in this case.

 

 

Above is the list of Events available for the Commandbutton CmdConvert.

 

Each Form has two kinds of routines (i.e. Sub/Function): the Event and the General ones. If you removed a control that has an Event routine that Event routine still exists as a general routine.

 

 

Some controls like Frame, PictureBox are container controls. Form itself is a kind of container control. A container control can contain other controls. When you move a container all the controls contained in it are also moved. Note that it’s possible to have a control sitting on top of a container control but does not belong to (contained by) the container control.

 

Mousedown (used for Drag) ' Use MouseDown/MouseUp when Right Click or combine Click with SHIFT or CTRL. To find out what key was hold down, check the Button and Shift values.

Each Click event also has a MouseDown and a MouseUp event. MouseDown and MouseUp events also return the coordinates (position) of the mouse relative to the top left corner of the control’s container.

 

KeyPress

Example:

Private Sub Text1_KeyPress(KeyAscii As Integer)

' Treat Enter key like TAB key

If KeyAscii = 13 then

KeyAscii = 0 ‘ Eliminate the Enter keyascii to avoid side effect.

Sendkeys "{TAB}" ‘ Emulate pressing the Tab key

End If

End Sub

Certain keystrokes are not captured by KeyPress. In that case use KeyDown event which returns both the Keycode and Shift.

Change

Example:

Private Sub Text1_Change()

CmdConvert_Click ' Emulate a click of CommandButton CmdConvert

End Sub

Use the Change event of a Textbox carefully to avoid the Change Event Sub calling itself.

GotFocus ' gets the cursor. Opportunity to tell user that the program is ready to receive next input keystroke. For example, change the backcolor of the textbox.

LostFocus ' The cursor is moving to the next control in TabIndex order. You can check validity of entered data on LostFocus event

DragDrop ' Implement action for the Control on which another Control has just been dropped. Use DragOver to give visual feedback to user that a Drop can be carried out on the target Control. Don’t forget to assign a DragIcon to the Control that is being dragged, otherwise the outline of the whole control will drag.

VB Project

The VB project file (.vbp) is a text file. It contains:

• the list of ActiveXs and References that are required by the application
• the list of Forms, Modules and Classes etc
• all other information about the project. Any of these can be changed by using the Project | Properties menu command.

Form ASCII file is stored as a text file, extension *.FRM . It has two parts:

• the description of the Visual Components. Basing on this information VB can reconstruct the picture of the form with all its controls on the screen.
• the MSBasic Codes.

 

The Visual Control description part may include Menu details.

Form Graphic: File extension *.FRX. This file type contains the graphic part such as Picture, Icons of the form.

Modules has no Visual Control parts. It is visible by all Forms, ie. Any form can refer to the module's variables and Subs/Functions provided these items are declared Public.