StringBuilder.AppendFormat Method (IFormatProvider, String, Object())
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Appends the string returned by processing a composite format string, which contains zero or more format items, to this instance. Each format item is replaced by the string representation of a corresponding argument in a parameter array using a specified format provider.
Assembly: mscorlib (in mscorlib.dll)
'Declaration Public Function AppendFormat ( _ provider As IFormatProvider, _ format As String, _ ParamArray args As Object() _ ) As StringBuilder
Parameters
- provider
- Type: System.IFormatProvider
An object that supplies culture-specific formatting information.
- format
- Type: System.String
A composite format string (see Remarks).
- args
- Type:
System.Object
()
An array of objects to format.
Return Value
Type: System.Text.StringBuilderA reference to this instance after the append operation has completed. After the append operation, this instance contains any data that existed before the operation, suffixed by a copy of format, where each format item is replaced by the string representation of the corresponding object argument.
| Exception | Condition |
|---|---|
| ArgumentNullException | format is Nothing. |
| FormatException | format is invalid. -or- The index of a format item is less than 0 (zero), or greater than or equal to the length of the args array. |
| ArgumentOutOfRangeException | The length of the expanded string would exceed the maximum capacity of this instance. |
This method uses the Composite Formatting of the .NET Framework to convert the value of an object to its text representation and embed that representation in the current StringBuilder object.
The format parameter consists of zero or more runs of text intermixed with zero or more indexed placeholders, called format items, that correspond to objects in the parameter list of this method. The formatting process replaces each format item with the string representation of the corresponding object.
The syntax of a format item is as follows:
{index[,length][:formatString]}
Elements in square brackets are optional. The following table describes each element.
Element | Description |
|---|---|
index | The zero-based position in the parameter list of the object to be formatted. If the object specified by index is Nothing, the format item is replaced by String.Empty. If there is no parameter in the index position, a FormatException is thrown. |
,length | The minimum number of characters in the string representation of the parameter. If positive, the parameter is right-aligned; if negative, it is left-aligned. |
:formatString | A standard or custom format string that is supported by the parameter. |
Note: |
|---|
For the standard and custom format strings used with date and time values, see Standard Date and Time Format Strings and Custom Date and Time Format Strings. For the standard and custom format strings used with numeric values, see Standard Numeric Format Strings and Custom Numeric Format Strings. For the standard format strings used with enumerations, see Enumeration Format Strings. |
The provider parameter specifies an IFormatProvider implementation that can provide formatting information for the objects in args. provider can be any of the following:
A CultureInfo object that provides culture-specific formatting information.
A NumberFormatInfo object that provides culture-specific formatting information for numeric values in args.
A DateTimeFormatInfo object that provides culture-specific formatting information for date and time values in args.
A custom IFormatProvider implementation that provides formatting information for one or more of the objects in args. Typically, such an implementation also implements the ICustomFormatter interface. The second example in the next section illustrates an StringBuilder.AppendFormat(IFormatProvider, String, Object()) method call with a custom IFormatProvider implementation.
If the provider parameter is Nothing, format provider information is obtained from the current culture.
args represents the objects to be formatted. Each format item in format is replaced with the string representation of the corresponding object in args. If the format item includes formatString and the corresponding object in args implements the IFormattable interface, then args[index].Format(formatString, provider) defines the formatting. Otherwise, args[index].ToString(provider) defines the formatting.
The following example demonstrates the AppendFormat method.
Imports System.Text Imports System.Globalization Class Example Private Shared sb As New StringBuilder() Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock) Dim var1 As Integer = 111 Dim var2 As Single = 2.22F Dim var3 As String = "abcd" Dim var4 As Object() = {3, 4.4, "X"c} outputBlock.Text &= vbCrLf outputBlock.Text &= "StringBuilder.AppendFormat method:" & vbCrLf sb.AppendFormat("1) {0}", var1) Show(outputBlock, sb) sb.AppendFormat("2) {0}, {1}", var1, var2) Show(outputBlock, sb) sb.AppendFormat("3) {0}, {1}, {2}", var1, var2, var3) Show(outputBlock, sb) sb.AppendFormat("4) {0}, {1}, {2}", var4) Show(outputBlock, sb) Dim ci As New CultureInfo("es-ES") sb.AppendFormat(ci, "5) {0}", var2) Show(outputBlock, sb) End Sub 'Main Public Shared Sub Show(ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal sbs As StringBuilder) outputBlock.Text &= sbs.ToString() & vbCrLf sb.Length = 0 End Sub 'Show End Class 'Sample ' 'This example produces the following results: ' 'StringBuilder.AppendFormat method: '1) 111 '2) 111, 2.22 '3) 111, 2.22, abcd '4) 3, 4.4, X '5) 2,22
The following example defines a custom IFormatProvider implementation named CustomerFormatter that formats a 10-digit customer number with hyphens after the fourth and seventh digits. It is passed to the StringBuilder.AppendFormat(IFormatProvider, String, Object()) method to create a string that includes the formatted customer number and customer name.
Imports System.Text Public Class Customer Private custName As String Private custNumber As Integer Public Sub New(ByVal name As String, ByVal number As Integer) custName = name custNumber = number End Sub Public ReadOnly Property Name() As String Get Return Me.custName End Get End Property Public ReadOnly Property CustomerNumber() As Integer Get Return Me.custNumber End Get End Property End Class Public Class CustomerNumberFormatter Implements IFormatProvider, ICustomFormatter Public Function GetFormat(ByVal formatType As Type) As Object _ Implements IFormatProvider.GetFormat If formatType Is GetType(ICustomFormatter) Then Return Me End If Return Nothing End Function Public Function Format(ByVal fmt As String, ByVal arg As Object, ByVal provider As IFormatProvider) As String _ Implements ICustomFormatter.Format If TypeOf arg Is Int32 Then Dim custNumber As String = CInt(arg).ToString("D10") Return custNumber.Substring(0, 4) + "-" + custNumber.Substring(4, 3) + _ "-" + custNumber.Substring(7, 3) Else Return Nothing End If End Function End Class Module Example Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock) Dim customer As New Customer("A Plus Software", 903654) Dim sb As New StringBuilder() sb.AppendFormat(New CustomerNumberFormatter, "{0}: {1}", _ customer.CustomerNumber, customer.Name) outputBlock.Text &= sb.ToString() & vbCrLf End Sub End Module ' The example displays the following output: ' 0000-903-654: A Plus Software
Note: