Si lo que quieres es limitar la cantidad de caracteres de un String, puedes utilizar el buffer de un
StringBuilder:
Dim sb As New StringBuilder(1, 5) ' máximo 5 caracteres.
sb.Append("123456") ' 6 caracteres, dará error por sobrepasar el límite.
Si lo que quieres es un String de longitud variable pero que en principio contenga un número específico de caracteres, puedes usar el constructor del datatype String:
Dim str As New String(" "c, 10)
Si lo que quieres es crear un string de longitud fija, siempre puedes crear tu propia extensión de método, o type:
Modo de empleo:
Dim fixedStr As FixedLengthString
fixedStr = New FixedLengthString("", 10)
MessageBox.Show("""" & fixedStr.ValueFixed & """") ' Result: " "
fixedStr.ValueUnfixed = "12345"
MessageBox.Show("""" & fixedStr.ValueFixed & """") ' Result: "1245 "
fixedStr.ValueUnfixed = "1234567890abc"
MessageBox.Show("""" & fixedStr.ValueFixed & """") ' Result: "1234567890"
Source:
' ***********************************************************************
' Author : Elektro
' Modified : 04-February-2015
' ***********************************************************************
' <copyright file="FixedLengthString.vb" company="Elektro Studios">
' Copyright (c) Elektro Studios. All rights reserved.
' </copyright>
' ***********************************************************************
''' <summary>
''' Defines a <see cref="String"/> with a fixed length.
''' </summary>
Public NotInheritable Class FixedLengthString
#Region " Properties "
''' <summary>
''' Gets or sets the fixed string length.
''' </summary>
''' <value>The fixed string length.</value>
Public Property FixedLength As Integer
Get
Return Me.fixedLength1
End Get
Set(ByVal value As Integer)
Me.fixedLength1 = value
End Set
End Property
''' <summary>
''' The fixed string length.
''' </summary>
Private fixedLength1 As Integer
''' <summary>
''' Gets or sets the padding character thath fills the string.
''' </summary>
''' <value>The padding character thath fills the string.</value>
Public Property PaddingChar As Char
Get
Return Me.paddingChar1
End Get
Set(ByVal value As Char)
Me.paddingChar1 = value
End Set
End Property
''' <summary>
''' The padding character thath fills the string.
''' </summary>
Private paddingChar1 As Char
''' <summary>
''' Gets or sets the unmodified string.
''' </summary>
''' <value>The unmodified string.</value>
Public Property ValueUnfixed As String
Get
Return Me.valueUnfixed1
End Get
Set(ByVal value As String)
Me.valueUnfixed1 = value
End Set
End Property
''' <summary>
''' The unmodified string.
''' </summary>
Private valueUnfixed1 As String
''' <summary>
''' Gets the fixed string.
''' </summary>
''' <value>The fixed string.</value>
Public ReadOnly Property ValueFixed As String
Get
Return Me.FixLength(Me.valueUnfixed1, Me.fixedLength1, Me.paddingChar1)
End Get
End Property
#End Region
#Region " Constructors "
''' <summary>
''' Prevents a default instance of the <see cref="FixedLengthString" /> class from being created.
''' </summary>
Private Sub New()
End Sub
''' <summary>
''' Initializes a new instance of the <see cref="FixedLengthString" /> class.
''' </summary>
''' <param name="value">The string value.</param>
''' <param name="fixedLength">The fixed string length.</param>
''' <param name="paddingChar">The padding character thath fills the string.</param>
Public Sub New(ByVal value As String,
ByVal fixedLength As Integer,
Optional ByVal paddingChar As Char = " "c)
Me.valueUnfixed1 = value
Me.fixedLength1 = fixedLength
Me.paddingChar1 = paddingChar
End Sub
#End Region
#Region " Public Methods "
''' <summary>
''' Returns a <see cref="System.String" /> that represents this instance.
''' </summary>
''' <returns>A <see cref="System.String" /> that represents this instance.</returns>
Public Overrides Function ToString() As String
Return Me.ValueFixed
End Function
#End Region
#Region " Private Methods "
''' <summary>
''' Fixes the length of the specified string.
''' </summary>
''' <param name="value">The string value.</param>
''' <param name="fixedLength">The fixed string length.</param>
''' <param name="paddingChar">The padding character thath fills the string.</param>
''' <returns>System.String.</returns>
Private Function FixLength(ByVal value As String,
ByVal fixedLength As Integer,
ByVal paddingChar As Char) As String
If (value.Length > fixedLength) Then
Return value.Substring(0, fixedLength)
Else
Return value.PadRight(fixedLength, paddingChar)
End If
End Function
#End Region
End Class
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