Properties,Methods and Events

Properties describe objects. Methods cause an object to do something. Events are what happens when an object does something.

Every object, such as a form or control, has a set of properties that describe it. Although this set isn't identical for all objects, some properties--such as those listed in Table 1--are common to most controls. You can see every property for a given control by looking at the Properties window in the IDE.

TABLE 1  Common Properties of Visual Basic Controls

Property	Description
Left	The position of the left side of a control with respect to its container
Top	The position of the top of a control with respect to its container
Height	A control's height
Width	A control's width
Name	The string value used to refer to a control
Enabled	The Boolean (True/False) value that determines whether users can manipulate the control
Visible	The Boolean (True/False) value that determines whether users can see the control

Another important property to consider is BorderStyle, which determines the window elements (title bar, Maximize and Minimize buttons, and so forth) a form will have. Table 2 summarizes the six BorderStyle settings;

TABLE 2  The Six Settings of the BorderStyle Property

Setting	Description
0-None	No borders, no title bar, not movable. Use this as a backdrop for a splash screen.
Setting	Description
1-Fixed Single	Not sizable by dragging borders but can have Maximize and Minimize buttons. Use this for any fixed-size window for which you want a button to appear in the taskbar.
2-Sizable (default)	Sizable by dragging borders and by using Maximize and Minimize buttons. Use this for typical programs.
3-Fixed Dialog	Not sizable and no Maximize/Minimize buttons. Use this for simple forms such as a password dialog.
4-Fixed ToolWindow	Similar to 3-Fixed Dialog except that the title bar is shorter and the title bar font and Close button are correspondingly smaller. Use this for floating toolbars.
5-Sizable ToolWindow	Similar to a 4-Fixed ToolWindow except that it's sizable by dragging the border. Use this for windows such as the Visual Basic Properties window.

Methods are blocks of code designed into a control that tell the control how to do things, such as move to another location on a form. Just as with properties, not all controls have the same methods, although some common methods do exist, as shown in Table 3.

TABLE 3  Common Methods of Visual Basic Controls

Method	Use
Move	Changes an object's position in response to a code request
Drag	Handles the execution of a drag-and-drop operation by the user
SetFocus	Gives focus to the object specified in the method call
ZOrder	Determines the order in which multiple objects appear onscreen

Events are what happen in and around your program. For example, when a user clicks a button, many events occur: The mouse button is pressed, the CommandButton in your program is clicked, and then the mouse button is released. These three things correspond to the MouseDown event, the Click event, and the MouseUp event. During this process, the GotFocus event for the CommandButton and the LostFocus event for whichever object previously held the focus also occur.

Again, not all controls have the same events, but some events are shared by many controls (see Table 4). These events occur as a result of some specific user action, such as moving the mouse, pressing a key on the keyboard, or clicking a text box. These types of events are user-initiated events and are what you will write code for most often.

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Using GotFocus and LostFocus

The GotFocus and LostFocus events relate to most other events because they occur whenever a new control becomes active to receive user input. This makes GotFocus and LostFocus useful for data validation, the process of making sure that data is in the proper format for your program. Be careful, though! Improperly coding these two events can cause your program to begin an endless loop, which will cause your program to stop responding.

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TABLE 4  Common Events of Visual Basic Controls

Event	Occurrence
Change	The user modifies text in a combo box or text box.
Click	The user clicks the primary mouse button on an object.
DblClick	The user double-clicks the primary mouse button on an object.
DragDrop	The user drags an object to another location.
DragOver	The user drags an object over another control.
GotFocus	An object receives focus.
KeyDown	The user presses a keyboard key while an object has focus.
KeyPress	The user presses and releases a keyboard key while an object has focus.
KeyUp	The user releases a keyboard key while an object has focus.
Event	Occurrence
LostFocus	An object loses focus.
MouseDown	The user presses any mouse button while the mouse pointer is over an object.
MouseMove	The user moves the mouse pointer over an object.
MouseUp	The user releases any mouse button while the mouse pointer is over an object.