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AdjustableControl Class

  + Object
    + Display
      + UIComponent
        + Control
          + AdjustableControl

Description

The AdjustableControl class implements the common behaviors of controls that allow selection of a ranged numeric value. Its derived classes are Scrollbar, Slider and SpinButton. Like all the classes derived from UIComponent, this class is not instantiable, cloneable or derivable. The only instances available to the programmer are those automatically generated by HB++ when you place this control on a form.

The range of valid values is defined by the Min and Max properties, the current value being held in the Value property. When the user clicks between the cursor and one of the extremes of the control, the current value is increased or decreased by the value held by LargeChange. The SetValues method allows all these values to be modified together.

The Track event is raised when the user moves the cursor whilst the Scroll event is raised when the user releases the cursor. Note: This event is not raised by the SpinButton control.

The example below which should be copied onto a form containing a scrollbar and a field, implements a metronome. The user chooses the number of beats per minute by scrolling a scrollbar.

Private T as New Timer

Private Sub Form_Load()
  Scrollbar1.SetValues 40, 240, 10, 90
  Scrollbar1_Scroll Scrollbar1.Value
  T.Enabled = True
End Sub

Private Sub Form_Unload()
  T.Enabled = False
End Sub

Private Sub Scrollbar1_Track(ByVal iValue As Integer)
  Field1.Text = iValue & " bpm"
End Sub

Private Sub Scrollbar1_Scroll(ByVal iValue As Integer)
  Scrollbar1_Track iValue
  T.Interval=60000/CLng(iValue)
End Sub

Private Sub T_Timer()
  Beep 100, 20
End Sub

Note that the Track event is intercepted to update the contents of field, giving the user feedback on the current position of the cursor, whilst the Scroll event is used to update the timer itself.

Members

System requirements