Controls General Discussion VB Controls Visual Basic Controls

Controls General Discussion

VB Controls

Visual Basic Controls • A control is the generic name for any object placed on a form • Controls may be images, text boxes, buttons, pulldown menus, active-X controls, OLE objects, etc. • Each control type has its own set of methods, properties and events • Each control instantiation is given a unique name and is a unique entity

Control Placement • Controls are available from the control toolbox • Click to highlight the desired control • Click and drag to place it on the form in the location and size you want • Alternatively, double-click on the control and it will be placed in the middle of the form • After it is placed, its size and position can be altered as desired (mouse or ctrl-arrow to move, shift-arrow to size)

Using the Grid • The grid is used to “snap” positions and sizes to grid increments - helps in making your form neat. • Use the grid to keep things aligned • Tools/Options/General will allow you to turn the grid on and off and to change the spacing • Controls can be locked in place with the Format/Lock option – Prevents mouse from accidentally altering, but Ctrl/Shift-Arrows can still change position/size

Copying Controls (1) • A control identical to one just created can be made by: – – selecting the desired control pressing Ctrl-C (copy) pressing Ctrl-V (paste) moving the new control to the desired position • Note that when you paste the copy, you will be asked if you want a control array or just another control

Copying Controls (2) • You will be asked if this is part of a control array (the choice depends on what you are trying to accomplish) – If NO, then a new control with the next higher name will be created but with the same caption/text property (a copy of text 1 is text 2) – If YES, then a new control with the same name will be created, but with the next higher index number (an array copy of text 1 becomes text 1(1) and the original is text 1(0)) Note that all controls in an array share events but have individual properties

Basic Controls • Command Button – Main purpose is to make something happen – Default event is click • Text Box – Used for user data entry and simple result output – Default event is change • Label Control – A “do nothing” control for adding text to the form – Default event is click

Basic Controls (2) • Checkbox Control – Used for selecting options (e. g. setting variables which are tested by the program) – Default event is click – Multiple boxes may be checked • Option (Radio) Button Control – Used to select one (and only one) of many mutually exclusive options – Default event is click – Only one option set per form unless in a frame

Picturebox Control • Used to add a picture to a form (. bmp, . wmf, . gif, . jpg, . ico) • The Autosize property will cause the picturebox to expand/shrink to fit the picture. • If you make the picturebox smaller than the picture it will clip • Most used properties are name and picture • Default method is click • Much more functional than images

Image Control • Adds a scaled image Used to add a picture to a form (. bmp, . wmf, . gif, . jpg, . ico) • The image will be scaled to fit inside whatever box size you draw • Set the stretch property to true to permit altering the displayed control size. • Most used properties are name and picture • Default method is click • Cannot be placed on top of other controls or have focus at run time

Timer Control • Timer is visible only at design time • The enabled property enables or suspends the timer operation (unlike other controls) • The interval property determines how often the timer's timer event is triggered • Only a single event indicating timeout has occured

Common Control Properties • Enabled - allows alteration at run time – If false, control is grayed out at run time • Visible - visible to user at run time • tabindex - controls order that the tab key sequences through controls on a form at runtime

Other Controls • • Frame Control Combo. Box Control List. Box Control HScroll. Bar VScroll. Bar Controls Timer Control Drive. List. Box Control Dir. List. Box Control n n File. List. Box Control Shape Control – n n n rectangle, square, oval circle, rounded square, rounded rectangle Line Control Data Selection control OLE Control

Writing Event Handlers (1) • Open the Code window for the control – double-click on the control itself or – click the code-window icon on the Project Explorer and select the control-name of interest • Select the event of interest from the pull-down selection box if the default is not what you want. – Alternatively you could type the whole thing in, but it’s too easy to make a simple naming mistake • Enter your event-handler code between the Private Sub object_event() and End Sub lines

Writing Event Handlers (2) • Use indenting (tab) to make the code easier to read (and debug) • Keep names meaningful and short • Watch out for red lines (indicating errors) • Use completions and selections rather than typing in the full whatever • Use msgbox() for simple debugging

Form Events/Methods • form_load() - invoked when the form is first loaded. Does not display the form except for the startup form and then only on completion • form_unload() - invoked when the form is exited or otherwise terminated • [object. ]show - normally, a form is not displayed when it is loaded. Show overrides this.