Week 7

1
Week 7

• The Windows API
• Sound and Images

2
Dynamic link library files

• This is the first example we have come across of
  using pre-defined library functions-in this case
  to play a sound. These are sourced from dynamic
  link libraries (.dll) files in this case the
  winmm.dll.

3
What is the API?

• The Application Windows Interface (API) is an
  interface to the many routines made available
  through Dynamic Link Libraries (DLLs) containing
  thousands of functions and procedures.
• These are available for you to use in your
  applications
• Think of them as a toolbox of extra programming
  tools

4
Adding a .wav file to the application

• The first tutorial involves calling a pre-defined
  library dll called winmm.dll (Win multimedia)

5
Write the following code to the General
declarations section of the form.

• Private Declare Function sndPlaySound Lib
  "winmm.dll" Alias "sndPlaySoundA" (ByVal
  lpszSoundName As String, ByVal uFlags As Long) As
  Long
• ' Play AsynchronouslyConst SND_ASYNC H1

6
Write the following codebehind a command button

• Private Sub cmdChimes_Click()throw
  sndPlaySound("C\windows\media\chimes.wav",
  SND_ASYNC)End Sub

7
Image control

• Use the Image control to display a graphic. An
  Image control can display a graphic from a
  bitmap, icon, or metafile, as well as enhanced
  metafile, JPEG, or GIF files.

8
Inserting images

• We are going to start buy inserting card suit
  shape .ico files from Windows

9
Twips

• Visual Basic uses a device-independent unit of
  measurement, a twip, for calculating size and
  position. Two properties of the Screen object,
  TwipsPerPixelX and TwipsPerPixelY, can be used to
  determine the size of the display at run time.

10
For example-to adjust an image's location

• imgShape.Left 0
• ' Number of twips from left of Form window
• imgShape.Top 3820
• ' Number of twips from top of Form window

11

• The Image control uses fewer system resources and
  repaints faster than a PictureBox control, but it
  supports only a subset of the PictureBox
  properties, events, and methods. Although you can
  place an Image control within a container, an
  Image control can't act as a container.

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Image Control

• An Image control can display a graphic from a
  bitmap file. A bitmap defines an image as a
  pattern of dots (pixels). A bitmap has the file
  name extensions .bmp, .dib, or .2bp. You can use
  bitmaps of various color depths, including 2, 4,
  8, 16, 24, and 32-bits, but a bitmap only
  displays correctly if the display device supports
  the color depth used by the bitmap.
• For example, an 8-bit-per-pixel (256 color)
  bitmap only displays in 16 colors when shown on a
  4-bit-per-pixel (16 color) device.

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Picture

• Returns or sets a graphic to be displayed in a
  control.
• Syntax
• object.Picture picture
• The parts of the Picture property syntaxes are
  described in the following table.
• PartDescriptionpictureA string expression
  specifying a file containing a graphic, as
  described in Settings.

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Settings

• The settings for picture are described
• SettingDescription(None)(Default) No
  picture.BitmapSpecifies a graphic. You can load
  the graphic from the Properties window at design
  time. At run time, you can also set this property
  using the file name of a bitmap.Remarks
• At run time, the Picture property can be set to
  any other Picture property. Images are always
  specified by file name.
•  

15
Syntaxobject.Drag action

• The Drag method syntax has these parts
• PartDescriptionobjectRequired. An object
  expression that evaluates to an object in the
  Applies To list.
• If object is omitted, the object whose event
  procedure contains the Drag method is
  assumed.actionOptional. A constant or value that
  specifies the action to perform, as described in
  Settings. If action is omitted, the default is to
  begin dragging the object.Settings
• The settings for action are
• ConstantValueDescriptionvbCancel
• Cancels drag operation
• vbBeginDrag
• Begins dragging objectvbEndDrag
• Ends dragging and drop object

16
The Images Application

• The form shown uses four image controls, a shape
  control, a picture box, and a command button.
  When the user selects a playing card symbol, the
  shape control highlights the symbol and a
  description is displayed in the picture box. For
  a working version of this example, see Images.frm
  in the Controls.vbp sample application.

17
Image and shape control example
18
The following table lists the property settings
for the objects in the application
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(No Transcript)
20
Code

• The code in the image control Click event looks
  like this
• Private Sub imgHeart_Click()
• shpCard.Left imgClub.Left
• picStatus.Cls picStatus.Print "Selected Club"
  shpCard.Visible True
• End Sub

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Invoking methods

• Note that the first line in the Click event code
  assigns a value (the Left property of the image
  control) to the Left property of the shape
  control using the operator. The next two lines
  invoke methods, so no operator is needed. In the
  third line, the value ("Selected Club") is an
  argument to the Print method.

22

• There is one more line of code in the application
  that is of interest
• it is in the Form Load event.
• shpCard.Visible False
• By setting the Visible property of the shape
  control to False, the shape control is hidden
  until the first image is clicked. The Visible
  property is set to True as the last step in the
  image control Click event.