Puzzling Exception ("Invalid parameter") Thrown by MeasureCharacterRanges

  • Thread starter Thread starter eBob.com
  • Start date Start date
E

eBob.com

I have some code which is trying to determine where text will wrap in a
custom text box (which Inherits from Control). It determines the number of
characters which will fit in the first line, but then encounters an
exception when it calls MeasureCharacterRanges to see if the next character,
i.e. the one destined to become the first character of the second line, will
fit. The message says only "Invalid parameter" - it does not say which
parameter it did not like. And I can't find any problem with any of the
parameters.

The code uses an If loop to step from line to line and a Do loop within the
If loop to test how many characters will fit on the line. This code occurs
within the Property Set routine for the Text property:

Public Overrides Property Text() As String
Get
End Get

Set(ByVal Value As String)
Dim nlo As Integer = 0 'Next Line Offset (from
the top of the control)
Dim ll As Integer 'line length
Dim lo As Integer 'line offset of next
line

Dim cr(1) As CharacterRange
Dim strformat As New StringFormat
strformat.Alignment = StringAlignment.Near
Dim strregion(1) As Region
Dim measure_rect As New RectangleF
Dim mcr_rect As New RectangleF

MyBase.Text = Value

'build LineInfo array to facilitate scrolling
Dim grfx As Graphics = MyBase.CreateGraphics
lo = 0 'next line offset is
initially 0
mcr_rect = New RectangleF(0, 0, Me.ClientRectangle.Width,
Me.ClientRectangle.Height) 'for call
' to MeasureCharacterRanges
strformat.FormatFlags = StringFormatFlags.MeasureTrailingSpaces
For i As Integer = 0 To LIA_MaxSize
If i > (LIA_CurSize - 1) Then 'expand LIA if necessary
ReDim Preserve LIA(LIA_CurSize + LIA_ChunkSize)
LIA_CurSize += LIA_ChunkSize
End If
LIA(i).offset = lo 'set line offset
ll = 1 'initially try a line
length of 1
Do
cr(0) = New CharacterRange(lo, ll)
'MsgBox("trying """ & MyBase.Text.Substring(lo, ll) &
"""")
strformat.SetMeasurableCharacterRanges(cr)
strregion =
grfx.MeasureCharacterRanges(MyBase.Text.Substring(lo, ll), MyBase.Font, _
mcr_rect, strformat)
measure_rect = strregion(0).GetBounds(grfx)
If measure_rect.Width > MyBase.Width Then Exit Do
If measure_rect.Height > MyBase.Font.Height Then Exit Do
ll += 1 'try one more character next time through Do
loop
If (ll + lo) > MyBase.Text.Length Then Exit Do 'exit Do
if we're out of text
Loop
LIA(i).length = ll - 1
lo = lo + ll - 1
LIA_LastIndex += 1
If lo >= MyBase.Text.Length Then Exit For
Next
MsgBox(LIA_LastIndex.ToString & " lines")
End Set
End Property

I've struggled with this for hours so I sure hope someone sees whatever it
is that I am not seeing.

If anyone is inclined to play with the code the whole thing is pasted below.
The form has two NumericUpDown controls, nudWidth and nudHeight, and a
"Draw" button, btnDraw. Note that the OnPaint code is way out of date.

Thanks, Bob

Option Strict On
Option Explicit On

Imports System.ComponentModel
Imports System.drawing.drawing2d
Imports System.io

Public Class Form1
Inherits System.Windows.Forms.Form

Public sampstring As String = "The quick brown fox jumped over the lazy
dog."

Dim stb As New SpecialTextBox


#Region " Windows Form Designer generated code "

#End Region

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load

stb.Location = New Point(200, 100)
stb.Width = 60
nudWidth.Value = stb.Width
stb.Height = 200
nudHeight.Value = stb.Height


Dim tr As StreamReader
Dim tfn As String


dlgOpenTstFile.ShowDialog()
If dlgOpenTstFile.ShowDialog = DialogResult().OK Then

tfn = dlgOpenTstFile.FileName

End If

tr = New StreamReader(tfn)
'stb.Text = tr.ReadToEnd
stb.Text = sampstring

Controls.Add(stb)

End Sub

Private Sub btnDraw_Click(ByVal sender As Object, ByVal e As
System.EventArgs) Handles btnDraw.Click
'stb.Width = nudWidth.Value
'stb.Height = nudHeight.Value
stb.Refresh()
End Sub
End Class

Public Class SpecialTextBox
Inherits System.Windows.Forms.Control

Structure LineInfo
Public offset As Integer 'offset to first character in the line
Public length As Integer 'number of characters in the line
End Structure

Const LIA_ChunkSize As Integer = 5
Const LIA_MaxSize As Integer = 50000
Dim LIA_CurSize As Integer = LIA_ChunkSize
Dim LIA_ChunkNum As Integer = 1
Dim LIA_LastIndex As Integer = -1 'index of last line
in LIA
Private LIA(LIA_ChunkSize) As LineInfo 'LineInfo Array

Public Sub New()
MyBase.New()
End Sub
Public Overrides Property Text() As String
Get
End Get

Set(ByVal Value As String)
Dim nlo As Integer = 0 'Next Line Offset (from
the top of the control)
Dim ll As Integer 'line length
Dim lo As Integer 'line offset of next
line

Dim cr(1) As CharacterRange
Dim strformat As New StringFormat
strformat.Alignment = StringAlignment.Near
Dim strregion(1) As Region
Dim measure_rect As New RectangleF
Dim mcr_rect As New RectangleF

MyBase.Text = Value

'build LineInfo array to facilitate scrolling
Dim grfx As Graphics = MyBase.CreateGraphics
lo = 0 'next line offset is
initially 0
mcr_rect = New RectangleF(0, 0, Me.ClientRectangle.Width,
Me.ClientRectangle.Height) 'for call
' to MeasureCharacterRanges
strformat.FormatFlags = StringFormatFlags.MeasureTrailingSpaces
For i As Integer = 0 To LIA_MaxSize
If i > (LIA_CurSize - 1) Then 'expand LIA if necessary
ReDim Preserve LIA(LIA_CurSize + LIA_ChunkSize)
LIA_CurSize += LIA_ChunkSize
End If
LIA(i).offset = lo 'set line offset
ll = 1 'initially try a line
length of 1
Do
cr(0) = New CharacterRange(lo, ll)
'MsgBox("trying """ & MyBase.Text.Substring(lo, ll) &
"""")
strformat.SetMeasurableCharacterRanges(cr)
strregion =
grfx.MeasureCharacterRanges(MyBase.Text.Substring(lo, ll), MyBase.Font, _
mcr_rect, strformat)
measure_rect = strregion(0).GetBounds(grfx)
If measure_rect.Width > MyBase.Width Then Exit Do
If measure_rect.Height > MyBase.Font.Height Then Exit Do
ll += 1 'try one more character next time through Do
loop
If (ll + lo) > MyBase.Text.Length Then Exit Do 'exit Do
if we're out of text
Loop
LIA(i).length = ll - 1
lo = lo + ll - 1
LIA_LastIndex += 1
If lo >= MyBase.Text.Length Then Exit For
Next
MsgBox(LIA_LastIndex.ToString & " lines")
End Set
End Property




Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)

Dim rectf As RectangleF
Dim grfx As Graphics = e.Graphics
grfx.FillRectangle(Brushes.LightGray, Me.ClientRectangle)


'grfx.FillRectangle(Brushes.Yellow, 0, 0, 90, 20)
'rectf = New RectangleF(New PointF(0, 0), New
SizeF(Me.ClientRectangle.Width, Me.ClientRectangle.Height))
Dim nextoff As Integer = 0
Dim fh As Integer = Font.Height
Dim msr As SizeF 'MeasureString Result
Dim nlo As Integer = 0 'Next Line Offset (from the
top of the control)
Dim length As Integer
'Dim textlength = MyBase.Text.Length
Dim debugstr As String
For i As Integer = 0 To LIA_MaxSize
nlo = i * fh
length = 1
Do
msr = grfx.MeasureString(MyBase.Text.Substring(nextoff,
length), Font)
If msr.Width > Width Then Exit Do
length += 1
If (length + nextoff) > MyBase.Text.Length Then Exit Do
Loop
length -= 1
msr = grfx.MeasureString(MyBase.Text.Substring(nextoff, length),
Font)
grfx.FillRectangle(Brushes.White, 0, nlo, msr.Width, msr.Height)
grfx.DrawString(MyBase.Text.Substring(nextoff, length), Font,
Brushes.Black, 0, nlo)
debugstr = MyBase.Text.Substring(nextoff, length)
nlo = nlo + fh
nextoff = nextoff + length
If nextoff >= MyBase.Text.Length Then Exit For
Next

MyBase.OnPaint(e)

End Sub
End Class
 
eBob.com said:
I have some code which is trying to determine where text will wrap in a
custom text box (which Inherits from Control). It determines the number of
characters which will fit in the first line, but then encounters an
exception when it calls MeasureCharacterRanges to see if the next
character, i.e. the one destined to become the first character of the
second line, will fit. The message says only "Invalid parameter" - it does
not say which parameter it did not like. And I can't find any problem with
any of the parameters.

The code uses an If loop to step from line to line and a Do loop within
the If loop to test how many characters will fit on the line. This code
occurs within the Property Set routine for the Text property:

Public Overrides Property Text() As String
Get
End Get

Set(ByVal Value As String)
Dim nlo As Integer = 0 'Next Line Offset (from
the top of the control)
Dim ll As Integer 'line length
Dim lo As Integer 'line offset of next
line

Dim cr(1) As CharacterRange
Dim strformat As New StringFormat
strformat.Alignment = StringAlignment.Near
Dim strregion(1) As Region
Dim measure_rect As New RectangleF
Dim mcr_rect As New RectangleF

MyBase.Text = Value

'build LineInfo array to facilitate scrolling
Dim grfx As Graphics = MyBase.CreateGraphics
lo = 0 'next line offset is
initially 0
mcr_rect = New RectangleF(0, 0, Me.ClientRectangle.Width,
Me.ClientRectangle.Height) 'for call
' to MeasureCharacterRanges
strformat.FormatFlags = StringFormatFlags.MeasureTrailingSpaces
For i As Integer = 0 To LIA_MaxSize
If i > (LIA_CurSize - 1) Then 'expand LIA if
necessary
ReDim Preserve LIA(LIA_CurSize + LIA_ChunkSize)
LIA_CurSize += LIA_ChunkSize
End If
LIA(i).offset = lo 'set line offset
ll = 1 'initially try a line
length of 1
Do
cr(0) = New CharacterRange(lo, ll)
'MsgBox("trying """ & MyBase.Text.Substring(lo, ll) &
"""")
strformat.SetMeasurableCharacterRanges(cr)
strregion =
grfx.MeasureCharacterRanges(MyBase.Text.Substring(lo, ll), MyBase.Font, _
mcr_rect, strformat)
measure_rect = strregion(0).GetBounds(grfx)
If measure_rect.Width > MyBase.Width Then Exit Do
If measure_rect.Height > MyBase.Font.Height Then Exit
Do
ll += 1 'try one more character next time through Do
loop
If (ll + lo) > MyBase.Text.Length Then Exit Do 'exit Do
if we're out of text
Loop
LIA(i).length = ll - 1
lo = lo + ll - 1
LIA_LastIndex += 1
If lo >= MyBase.Text.Length Then Exit For
Next
MsgBox(LIA_LastIndex.ToString & " lines")
End Set
End Property

I've struggled with this for hours so I sure hope someone sees whatever it
is that I am not seeing.

If anyone is inclined to play with the code the whole thing is pasted
below. The form has two NumericUpDown controls, nudWidth and nudHeight,
and a "Draw" button, btnDraw. Note that the OnPaint code is way out of
date.

Thanks, Bob
Click to expand...

Well ... I have finally spotted the problem. When I invoke
MeasureCharacterRanges I am passing a substring as the first argument
(".Text.Substring(lo,ll)") but the CharacterRange assigned to the
StringFormat argument also contains the starting character and length of the
substring ...

cr(0) = New CharacterRange(lo, ll)
strformat.SetMeasurableCharacterRanges(cr)

This works for the first line where lo remains 0 and ll starts at 1 and is
incremented until the line is full. But the first time through the Do Loop
to determine how many characters will fit in the second line, lo is, for
example, 10 - so the first argument is passing a 1 character string and the
CharacterRange is specifying 1 character starting at the 10th character of
the first argument!

This is what happens when you start out using MeasureString and then switch
to MeasureCharacterRanges.

So ... "my bad", but it will be a cold day in hell before I forgive MS for
such an inprecise error message.

Bob
 
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