visualbasic lecture4.pdf
TRANSCRIPT
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Copyright 2011 Pearson Addison-Wesley
Addison Wesley
is an imprint of
2011 Pearson Addison-Wesley. All rights reserved.
Addison Wesley
is an imprint of
Chapter 3
Variables and Calculations
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Copyright 2011 Pearson Addison-Wesley
The TextBox Control
% text box is a rectangular area on a "or# that
accepts input "ro# a eyboard
Tutorial 3&1 pro'ides an exa#ple in the use o"a text box
Chapter 3& Slide 3
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Copyright 2011 Pearson Addison-Wesley
(sing the Text )roperty in Code
The TextBox control$s Text property can be
accessed in code the sa#e way you access
other properties
*or +xa#ple
The contents o" the Text property can be assigned
into a -abel control$s Text property
lblInfo.Text = txtInput.Text
The contents o" the Text property can be displayed
in a #essage box Chapter 3& Slide
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String Concatenation
%ssu#e the user has entered their na#e into
the TextBox txt2a#e
-abel lblGreeting can say, 4ello5 to any na#e"ound in the TextBox
lblreeting.Text = !"ello ! # txt$ame.Text
%ppends user na#e in txt2a#e.Text to 4ello 5and stores result in text property o" lblGreeting
Chapter 3& Slide 6
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String Concatenation
Tutorial 3&7 pro'ides another exa#ple o" how
to concatenate strings "ro# text boxes
Chapter 3& Slide 8
txtDayOfWee
ktxtMonth
txtDayOfMont
htxtYear
lblDateString
btnExitbtnClearbtnShowDate
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%ligning Controls in 9esign /ode
!hen dragging a control to a "or#, it can be
aligned with a control already on the "or#
Blue guide lines appear "or 'ertical align#ent
-a'ender guide lines "or hori:ontal align#ent
Chapter 3& Slide ;
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The *ocus /ethod
*or a control to ha'e the "ocus #eans that it is
ready to recei'e the user
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The *ocus /ethod
?ou can tell which control has "ocus by its
characteristics
!hen a TextBox has "ocus, it will ha'e a blining
cursor or its text will be highlighted
!hen a button, radio button, or a chec box has
"ocus, you$ll see a thin dotted line around the
control
Tutorial 3&3 shows an exa#ple o" the *ocus
#ethodChapter 3& Slide1@
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Controlling a *or#$s Tab =rder
with the TabIndex )roperty Tab ey steps "ocus "ro# one control to the
next
This order is set by the TabIndex property The Tab ey causes the "ocus to Au#p to the
control with the next highest TabIndex 'alue
The TabIndex property is best changed withthe Tab =rder option "ro# the View #enu
9isplays the "or# in tab order selection #ode
Set a new tab order by clicing the controls in theChapter 3& Slide11
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%ssigning eyboard %ccess eys to Buttons
Say your "or# had a button with the text
+xit on it
?ou can allow the user to acti'ate the buttonusing %lt&D instead o" a #ouse clic
Eust change the button text property to
+Fxit The character "ollowing the
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Setting the %ccept Button
The accept button is a button that is i#plicitly
acti'ated i" the user hits the +nter ey
The %cceptButton )roperty designates whichbutton on the "or# will beha'e in this #anner
The button cliced #ost "reuently on a "or#
is usually assigned as the accept button
Chapter 3& Slide1
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Setting the Cancel Button
The cancel button is a button that is i#plicitly
acti'ated i" the user hits the +scape ey
The CancelButton )roperty designates whichbutton on the "or# will beha'e in this #anner
%ny exit or cancel button on a "or# is a
candidate to beco#e the cancel button Tutorial 3& pro'ides exa#ples o" setting
access eys, accept, and cancel buttons
Chapter 3& Slide1
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Copyright 2011 Pearson Addison-Wesley
Addison Wesley
is an imprint of
2011 Pearson Addison-Wesley. All rights reserved.
Addison Wesley
is an imprint of
Section 3.7
Variables and 9ata Types
Variables hold data that #ay be
#anipulated, used to #anipulate other data, or re#e#bered "or later use.
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!hy 4a'e VariablesJ
% 'ariable is a storage location in the
co#puter$s #e#ory, used "or holding
in"or#ation while the progra# is running
The in"or#ation that is stored in a 'ariable
#ay change, hence the na#e 'ariable5
Chapter 3& Slide18
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!hat Can ?ou 9o !ith VariablesJ
Copy and store 'alues entered by the user, so
they #ay be #anipulated
)er"or# arith#etic on 'alues Test 'alues to deter#ine that they #eet so#e
criterion
Te#porarily hold and #anipulate the 'alue o"a control property
Ke#e#ber in"or#ation "or later use in the
progra# Chapter 3& Slide1;
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4ow to Thin %bout Variables
?ou the progra##er #ae up a na#e "or the
'ariable
Visual Basic associates that na#e with alocation in the co#puter
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9eclaring Variables
% 'ariable declaration is a state#ent that creates a 'ariable in
#e#ory
The syntax is
im ariable$ame *s ataType
imshort "or 9i#ensionH is a eyword
ariable$ameis the progra##er designated na#e
*sis a eyword
ataTypeis one o" #any possible eywords "or the type
o" 'alue the 'ariable will contain
Chapter 3& Slide7@