[RESOLVED] Problem with Color.FromName

[Poppa Mintin]

Hi,

I've been trying to use...

Dim myColour As Color = Color.FromName(TextBox1.Text)

...to give a user a choice of colour for Form background or, for example, Pen color.

I've run into a problem because 'Color.FromName' doesn't automatically detect an unknown colour or misspelling, if the text is unknown the code just returns Black.

Using...

     myColour = Color.FromName(TextBox2.Text)
     Me.BackColor = myColour

...however does produce a detectable error, and it's what I've been using.

In a previous thread jmcilhinney made this suggestion:

Dim names = {"Red", "Rid"}
 
For Each s In names
    If [Enum].IsDefined(GetType(KnownColor), s) Then
        Console.WriteLine($"There is a known colour named '{s}'.")
    Else
        Console.WriteLine($"There is NOT a known colour named '{s}'.")
    End If
Next

I can see how that would work but I don't really want to sit and add all 140 odd 'Known' colours to the string array 'names', not least because I can't type and produce far too many typo's at the best of times.

I've been trying, without success, to find where to access a 'look-up' list to compare the text with the known colours. I'm sure there must be a list somewhere in Visual Studio because a selection is presented each time a colour is selected in design.


Poppa

[jmcilhinney]

I've been trying, without success, to find where to access a 'look-up' list to compare the text with the known colours.

Um, the KnownColor enumeration that I just demonstrated for you. You don't have to add anything to any array. You seem to have missed the principle the example was demonstrating. The line that matters there is this one:

If [Enum].IsDefined(GetType(KnownColor), s) Then

where s is the String value you want to test. In your case, that String value is TextBox1.Text so you substitute that for s, e.g.

Dim colourName = TextBox1.Text
 
If [Enum].IsDefined(GetType(KnownColor), colourName) Then
    Dim colour = Color.FromName(colourName)
 
    'Use colour here.
Else
    'There is no such colour.
End If

[dday9]

To elaborate, Enum.IsDefined in this case returns a Boolean value showing whether a value's name exists in the KnownColor enumeration.

Behind the scenes, it is iterating over every 167 values and checking whether or not the value you passed is one of them.

Here is the relevant documentation: https://docs.microsoft.com/en-us/dot...enum.isdefined

[Poppa Mintin]

Um, the KnownColor enumeration that I just demonstrated for you. You don't have to add anything to any array. You seem to have missed the principle the example was demonstrating.

Sorry John, still got problem. You're right, I did miss what you meant.

So: this is how I interpreted your post:

Private Sub Colours()
        Dim colour(2) As Color
 
        colour(0) = Color.FromName(TextBox1.Text)
        colour(1) = Color.FromName(TextBox2.Text)
        For Each s In colour
            If [Enum].IsDefined(GetType(KnownColor), s) Then
                'Color ok
            Else
                StartUp()
                Label3.Show()
            End If
        Next
        pen1 = New Pen(colour(1), 1)
        Me.BackColor = colour(0)
        PictureBox1.BackColor = colour(0)
        PictureBox1.Show()
    End Sub

When I run this code I get this error at Line 7. (For reference the Line 90 as referenced in the copy below is Line 9 in the shown snippet.)

System.InvalidOperationException
HResult=0x80131509
Message=Unknown enum type.
Source=mscorlib
StackTrace:
at System.RuntimeType.IsEnumDefined(Object value)
at System.Enum.IsDefined(Type enumType, Object value)
at Polly_Draw.Form1.Colours() in D:\~VB Trials\Polly Draw\Form1.vb:line 90
at Polly_Draw.Form1.Button2_Click() in D:\~VB Trials\Polly Draw\Form1.vb:line 68
at Polly_Draw.Form1._Lambda$__R31-3(Object a0, EventArgs a1)
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoCompo nentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine)
at Polly_Draw.My.MyApplication.Main(String[] Args) in :line 81

This exception was originally thrown at this call stack:
[External Code]
Polly_Draw.Form1.Colours() in Form1.vb
Polly_Draw.Form1.Button2_Click() in Form1.vb
[External Code]

Which probably means that I've got it wrong again.


Poppa

PS.
Meant to say... This was with two valid colours, 'Red and Blue'.

Pop.

[dday9]

Do you have System.Drawing imported? I'm able to test JMcIlhinney's solution without any issues:

Imports System
Imports System.Drawing
Public Module Module1
    Public Sub Main()
        Dim input As String = Console.ReadLine()
        If [Enum].IsDefined(GetType(KnownColor), input) Then
            Console.WriteLine("{0} is a known color.", input)
        Else
            Console.WriteLine("{0} is not a known color.", input)
        End If

    End Sub
End Module

Fiddle: Live Demo

Screenshot:

[dbasnett]

It would help if you had Strict and Explicit on, something you've been told numerous times.

An experiment / hint

        Dim colour(2) As Color

        colour(0) = Color.FromName("Blue")
        colour(1) = Color.FromName("red")
        For Each s As String In From c In colour Select c.Name
            If [Enum].IsDefined(GetType(KnownColor), s) Then
                'Color ok
                Stop
            Else
                Stop
            End If
        Next

[Poppa Mintin]

It would help if you had Strict and Explicit on, something you've been told numerous times.

I thought I had both of those 'On' by default but can't find where to check.


Poppa

[.paul.]

You’re doing it wrong...

Colours(0) = Color.FroName(TextBox1.Text)

You said yourself in an earlier post that that doesn’t work, so why would it work now?
You’re supposed to be testing if a STRING color name exists in the knowncolors enum, before setting any colors.fromname

[Poppa Mintin]

Update.

I realised I had a basic error, I was checking a Color, not a String, so I've changed things a bit.

Private Sub Colours()
        Dim colour(2) As Color, chk(2) As String
 
        '   Ensure the input colours start with an upper case letter.
        chk(0) = TextBox1.Text
        chk(1) = TextBox2.Text
        chk(0) = chk(0).Substring(0, 1).ToUpper & chk(0).Substring(1)
        chk(1) = chk(1).Substring(0, 1).ToUpper & chk(1).Substring(1)
 
        For i = 0 To 1
            If [Enum].IsDefined(GetType(KnownColor), chk(i)) Then
                colour(i) = Color.FromName(chk(i))
            Else
                StartUp()
                Label3.Show()
                Exit Sub
            End If
        Next
        pen1 = New Pen(colour(1), 1)
        Me.BackColor = colour(0)
        PictureBox1.BackColor = colour(0)
        PictureBox1.Show()
    End Sub

Well at least my first attempt didn't throw up any errors but it failed to recognise 'red' as a colour.
Then I tried 'Red' and that worked correctly. So I added Lines 4 to 8.

Thanks guys


Poppa

[.paul.]

Why declare colours(2) and chk(2)???
You’re only using 2 elements in both. You know arrays are zero based, but you need to declare arrays with the Upperbound and not the Length...

I.e. colours(1), chk(1)

Edit: That’s how to declare and dimension an array in VB. In C languages, you do use the array Length when declaring and dimensioning...

[.paul.]

If TextBox1.Text = ‘red’ this is how to change it to ‘Red’
If it already is ‘Red’ and not ‘red’, no harm done...

chk(0) = StrConv(TextBox1.Text, vbProperCase)
chk(1) = StrConv(TextBox2.Text, vbProperCase)

[.paul.]

As you're using TextBoxes for inputting color names, I'd recommend using AutoComplete to avoid many errors. Here's an example...

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim source As New AutoCompleteStringCollection
        source.AddRange([Enum].GetNames(GetType(KnownColor)))

        TextBox1.AutoCompleteCustomSource = source
        TextBox1.AutoCompleteMode = AutoCompleteMode.SuggestAppend
        TextBox1.AutoCompleteSource = AutoCompleteSource.CustomSource

        TextBox2.AutoCompleteCustomSource = source
        TextBox2.AutoCompleteMode = AutoCompleteMode.SuggestAppend
        TextBox2.AutoCompleteSource = AutoCompleteSource.CustomSource

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim c1 As String = TextBox1.Text.ToLower
        Dim c2 As String = TextBox2.Text.ToLower

        Dim knownColorNames() As String = [Enum].GetNames(GetType(KnownColor))
        Dim knownColorNamesToLower() As String = [Enum].GetNames(GetType(KnownColor)).Select(Function(n) n.ToLower).ToArray
        Dim i1 As Integer = Array.IndexOf(knownColorNamesToLower, c1)
        Dim i2 As Integer = Array.IndexOf(knownColorNamesToLower, c2)
        If i1 > -1 AndAlso i2 > -1 Then
            c1 = knownColorNames(i1)
            c2 = knownColorNames(i2)
            TextBox1.ForeColor = Color.FromName(c1)
            TextBox1.BackColor = Color.FromName(c2)
            TextBox2.ForeColor = Color.FromName(c2)
            TextBox2.BackColor = Color.FromName(c1)
        End If
    End Sub

End Class

[jmcilhinney]

Keep in mind that the KnownColor enumeration contains values like Red, LightBlue and HighlightText. Here's a method that will match those values regardless of case while also excluding the system values:

Private Function IsColorName(name As String) As Boolean
    Dim knownColorNames = [Enum].GetNames(GetType(KnownColor))
 
    'Check for known colours, e.g. Red, LightBlue, Control.
    If Not knownColorNames.Any(Function(kcn) String.Equals(kcn, name, StringComparison.OrdinalIgnoreCase)) Then
        'The input does not match a known colour.
        Return False
    End If
 
    Dim systemColorNames = GetType(SystemColors).GetProperties(BindingFlags.Public Or BindingFlags.Static).Select(Function(pi) pi.Name)
 
    'Check for system colours, e.g. ButtonFace, Control, HighlightText.
    If systemColorNames.Any(Function(scn) String.Equals(scn, name, StringComparison.OrdinalIgnoreCase)) Then
        'The input matches a system colour.
        Return False
    End If
 
    'The specified colour is known but is not part of the system.
    Return True
End Function

Sample usage:

Dim colourNames = {"Red", "blue", "Groan", "control", "Window"}
 
For Each colourName As String In colourNames
    Console.WriteLine($"{colourName}: {IsColorName(colourName)}")
Next

You may also want to allow people to enter values like "light blue". A simple option would be to just remove the spaces from the input before comparing:

Private Function IsColorName(name As String) As Boolean
    name = name.Replace(" ", String.Empty)
 
    Dim knownColorNames = [Enum].GetNames(GetType(KnownColor))
 
    'Check for known colours, e.g. Red, LightBlue, Control.
    If Not knownColorNames.Any(Function(kcn) String.Equals(kcn, name, StringComparison.OrdinalIgnoreCase)) Then
        'The input does not match a known colour.
        Return False
    End If
 
    Dim systemColorNames = GetType(SystemColors).GetProperties(BindingFlags.Public Or BindingFlags.Static).Select(Function(pi) pi.Name)
 
    'Check for system colours, e.g. ButtonFace, Control, HighlightText.
    If systemColorNames.Any(Function(scn) String.Equals(scn, name, StringComparison.OrdinalIgnoreCase)) Then
        'The input matches a system colour.
        Return False
    End If
 
    'The specified colour is known but is not part of the system.
    Return True
End Function

The issue with that is that it will match "li ghtbl ue" as well as "light blue". The more rigorous option is to insert single spaces before upper-case letters within the field and property names:

Private Const SPACE As String = " "
 
Private Function IsColorName(name As String) As Boolean
    Dim knownColorNames As IEnumerable(Of String) = [Enum].GetNames(GetType(KnownColor))
 
    If name.Contains(SPACE) Then
        'The input contains at least one space so insert spaces into the known colour names for matching.
        knownColorNames = knownColorNames.Select(Function(kcn) InsertSpacesBetweenWords(kcn))
    End If
 
    'Check for known colours, e.g. Red, LightBlue, Control.
    If Not knownColorNames.Any(Function(kcn) String.Equals(kcn, name, StringComparison.OrdinalIgnoreCase)) Then
        'The input does not match a known colour.
        Return False
    End If
 
    Dim systemColorNames = GetType(SystemColors).GetProperties(BindingFlags.Public Or BindingFlags.Static).Select(Function(pi) pi.Name)
 
    If name.Contains(SPACE) Then
        'The input contains at least one space so insert spaces into the system colour names for matching.
        systemColorNames = systemColorNames.Select(Function(scn) InsertSpacesBetweenWords(scn))
    End If
 
    'Check for system colours, e.g. ButtonFace, Control, HighlightText.
    If systemColorNames.Any(Function(scn) String.Equals(scn, name, StringComparison.OrdinalIgnoreCase)) Then
        'The input matches a system colour.
        Return False
    End If
 
    'The specified colour is known but is not part of the system.
    Return True
End Function
 
Private Function InsertSpacesBetweenWords(text As String) As String
    For i = text.Length - 1 To 1 Step -1
        If Char.IsUpper(text(i)) Then
            text = text.Insert(i, SPACE)
        End If
    Next
 
    Return text
End Function

Sample usage:

Dim colourNames = {"Red", "blue", "Groan", "control", "Window", "light blue", "li    ghtbl ue", "highlight text", "hig hlightte xt"}
 
For Each colourName As String In colourNames
    Console.WriteLine($"{colourName}: {IsColorName(colourName)}")
Next

[.paul.]

If you wanted to give a color preview for your color selection process, you could use an extended combobox...

Public Class colorComboBox
    Inherits ComboBox

    Public Sub New()
        Me.DropDownStyle = ComboBoxStyle.DropDownList
        Me.DrawMode = Windows.Forms.DrawMode.OwnerDrawVariable
        MyBase.Items.Clear()
        MyBase.Items.AddRange([Enum].GetNames(GetType(KnownColor)).OrderBy(Function(n) Color.FromName(n).GetHue).ToArray)
    End Sub

    Protected Overrides Sub OnDrawItem(ByVal e As System.Windows.Forms.DrawItemEventArgs)
        Dim c As Color = Color.Empty
        If e.Index <> -1 Then
            c = Color.FromName(MyBase.Items(e.Index).ToString)
        End If
        If (e.State And DrawItemState.ComboBoxEdit) = DrawItemState.ComboBoxEdit Then
            ' Draw the contents of the edit area of the combo box.
            e.Graphics.FillRectangle(New SolidBrush(c), New Rectangle(4, e.Bounds.Top + 1, 16, 12))
            e.Graphics.DrawRectangle(Pens.Black, New Rectangle(4, e.Bounds.Top + 1, 16, 12))
            e.Graphics.DrawString(If(c.Name = "0", "Empty", c.Name), Me.Font, Brushes.Black, 22, e.Bounds.Top + 1)
        Else
            ' Draw the contents of an item in the drop down list.
            e.Graphics.FillRectangle(New SolidBrush(c), New Rectangle(2, e.Bounds.Top + 2, 16, 12))
            e.Graphics.DrawRectangle(Pens.Black, New Rectangle(2, e.Bounds.Top + 2, 16, 12))
            e.Graphics.DrawString(c.Name, Me.Font, Brushes.Black, 20, e.Bounds.Top + 2)
            ' Draw the focus rectangle.
            e.DrawFocusRectangle()
        End If
        MyBase.OnDrawItem(e)
    End Sub

    Public Function getSelectedColor() As Color
        If MyBase.SelectedIndex > -1 Then
            Return Color.FromName(MyBase.Text)
        Else
            Return Color.Transparent
        End If
    End Function

End Class

[Poppa Mintin]

Why declare colours(2) and chk(2)???
You’re only using 2 elements in both. You know arrays are zero based, but you need to declare arrays with the Upperbound and not the Length...

I.e. colours(1), chk(1)

Oh !
I've always used length, maybe from my original BASIC language from the 1970's.

Poppa

[.paul.]

Oh !
I've always used length, maybe from my original BASIC language from the 1970's.

Poppa

Color choice in your 70's BASIC would be easy. These days choosing knowncolors is more complicated. I'd still use my extended combobox. It avoids user error. Allowing text entry in a textbox for color choosing isn't an efficient method...

[Delaney]

If you wanted to give a color preview for your color selection process, you could use an extended combobox...

That's a nice tips, thanks (need to spread some rep before being able to give some to you).

I wonder if I can replace the colored rectangle with an image...?? I will try that as a good exercise.

[ChrisE]

If you wanted to give a color preview for your color selection process, you could use an extended combobox...

Public Class colorComboBox
    Inherits ComboBox

    Public Sub New()
        Me.DropDownStyle = ComboBoxStyle.DropDownList
        Me.DrawMode = Windows.Forms.DrawMode.OwnerDrawVariable
        MyBase.Items.Clear()
        MyBase.Items.AddRange([Enum].GetNames(GetType(KnownColor)).OrderBy(Function(n) Color.FromName(n).GetHue).ToArray)
    End Sub

    Protected Overrides Sub OnDrawItem(ByVal e As System.Windows.Forms.DrawItemEventArgs)
        Dim c As Color = Color.Empty
        If e.Index <> -1 Then
            c = Color.FromName(MyBase.Items(e.Index).ToString)
        End If
        If (e.State And DrawItemState.ComboBoxEdit) = DrawItemState.ComboBoxEdit Then
            ' Draw the contents of the edit area of the combo box.
            e.Graphics.FillRectangle(New SolidBrush(c), New Rectangle(4, e.Bounds.Top + 1, 16, 12))
            e.Graphics.DrawRectangle(Pens.Black, New Rectangle(4, e.Bounds.Top + 1, 16, 12))
            e.Graphics.DrawString(If(c.Name = "0", "Empty", c.Name), Me.Font, Brushes.Black, 22, e.Bounds.Top + 1)
        Else
            ' Draw the contents of an item in the drop down list.
            e.Graphics.FillRectangle(New SolidBrush(c), New Rectangle(2, e.Bounds.Top + 2, 16, 12))
            e.Graphics.DrawRectangle(Pens.Black, New Rectangle(2, e.Bounds.Top + 2, 16, 12))
            e.Graphics.DrawString(c.Name, Me.Font, Brushes.Black, 20, e.Bounds.Top + 2)
            ' Draw the focus rectangle.
            e.DrawFocusRectangle()
        End If
        MyBase.OnDrawItem(e)
    End Sub

    Public Function getSelectedColor() As Color
        If MyBase.SelectedIndex > -1 Then
            Return Color.FromName(MyBase.Text)
        Else
            Return Color.Transparent
        End If
    End Function

End Class

nice one

[.paul.]

I wonder if I can replace the colored rectangle with an image...?? I will try that as a good exercise.

You can draw anything you choose in the DrawItem event, but it helps to have something that relates to the item, as in this case...