IFormatProvider.GetFormat Method

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

Returns an object that provides formatting services for the specified type.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Syntax

Function GetFormat ( _
    formatType As Type _
) As Object
Object GetFormat(
    Type formatType
)

Parameters

  • formatType
    Type: System..::.Type
    An object that specifies the type of format object to return.

Return Value

Type: System..::.Object
An instance of the object specified by formatType, if the IFormatProvider implementation can supply that type of object; otherwise, nullNothingnullptra null reference (Nothing in Visual Basic).

Remarks

GetFormat is a callback method that formatting and parsing methods invoke to retrieve information about the format of the input string in parsing operations or the format of the output string in formatting operations. In the formatType parameter, the formatting or parsing method passes the type of object it requires to perform its operation. If the IFormatProvider implementation can supply this formatting or parsing object, it returns that object. If not, it returns nullNothingnullptra null reference (Nothing in Visual Basic).

For example, in the call to the Int32..::.ToString(IFormatProvider) method, the method argument is an IFormatProvider object that provides information about how the string representation of the current integer instance might be formatted. When the runtime executes the method, it calls the IFormatProvider object's GetFormat method and passes it a Type object that represents the NumberFormatInfo type. If the IFormatProvider object can supply a NumberFormatInfo object, it returns that object. If it cannot supply an object of that type, it returns nullNothingnullptra null reference (Nothing in Visual Basic).

You can implement the IFormatProvider interface and the GetFormat method in classes that provide custom formatting or parsing services. The IFormatProvider implementation is then passed as an argument to any overload of a parsing or formatting method that has a parameter of type IFormatProvider, such as String..::.Format(IFormatProvider, String, array<Object>[]()[]), Int32..::.ToString(String, IFormatProvider), or DateTime..::.Parse(String, IFormatProvider).

Examples

The following example illustrates the use of a class that implements the IFormatProvider interface and the GetFormat method. The AcctNumberFormat class converts an Int64 value that represents an account number to a formatted 12-digit account number. Its GetFormat method returns a reference to itself if the formatType parameter refers to a class that implements ICustomFormatter; otherwise, GetFormat returns nullNothingnullptra null reference (Nothing in Visual Basic).

Public Class AcctNumberFormat : Implements IFormatProvider, ICustomFormatter

   Private Const ACCT_LENGTH As Integer = 12

   Public Function GetFormat(ByVal formatType As Type) As Object _
                   Implements IFormatProvider.GetFormat
      If formatType Is GetType(ICustomFormatter) Then
         Return Me
      Else
         Return Nothing
      End If
   End Function

   Public Function Format(fmt As String, arg As Object, formatProvider As IFormatProvider) As String _
                          Implements ICustomFormatter.Format

      ' Provide default formatting if arg is not an Int64.
       If Not TypeOf arg Is Int64 Then
         Try 
            Return HandleOtherFormats(fmt, arg) 
         Catch e As FormatException 
            Throw New FormatException(String.Format("The format of '{0}' is invalid.", fmt), e)
         End Try
       End If   

      ' Provider default formatting for unsupported format strings.
      fmt = fmt.ToUpper(CultureInfo.InvariantCulture)
      If Not (fmt = "H" Or fmt = "I") Then
         Return HandleOtherFormats(fmt, arg)
      End If   

      ' Convert argument to a string.
      Dim result As String = arg.ToString()

      ' If account number is less than 12 characters, pad with leading zeroes.
      If result.Length < ACCT_LENGTH Then result = result.PadLeft(ACCT_LENGTH, "0"c)
      ' If account number is more than 12 characters, truncate to 12 characters.
      If result.Length > ACCT_LENGTH Then result = Left(result, ACCT_LENGTH)   

      If fmt = "I"                              ' Integer-only format.
         Return result
      ' Add hyphens for H format specifier.
      Else If fmt.ToUpper = "H"                 ' Hypenated format.
         Return Left(result, 5) & "-" & Mid(result, 6, 3) & "-" & Right(result, 4)
      ' This branch should never be reached.
      Else
         Try 
            Return HandleOtherFormats(fmt, arg) 
         Catch e As FormatException 
            Throw New FormatException(String.Format("The format of '{0}' is invalid.", fmt), e)
         End Try
      End If   
   End Function   

   Private Function HandleOtherFormats(fmt As String, arg As Object) As String
      If TypeOf arg Is IFormattable Then
         Return DirectCast(arg, IFormattable).ToString(fmt, CultureInfo.CurrentCulture)
      ElseIf arg IsNot Nothing Then
         Return arg.ToString()
      Else
         Return String.Empty
      End If
   End Function
End Class
public class AcctNumberFormat : IFormatProvider, ICustomFormatter
{
   private const int ACCT_LENGTH = 12;

   public object GetFormat(Type formatType)
   {
      if (formatType == typeof(ICustomFormatter))
         return this;
      else
         return null;
   }

   public string Format(string fmt, object arg, IFormatProvider formatProvider) 
   {
      // Provide default formatting if arg is not an Int64.
      if (arg.GetType() != typeof(Int64))
         try {
            return HandleOtherFormats(fmt, arg); 
         }
         catch (FormatException e) {
            throw new FormatException(String.Format("The format of '{0}' is invalid.", fmt), e);
         }

      // Provide default formatting for unsupported format strings.
      fmt = fmt.ToUpper(CultureInfo.InvariantCulture);
      if (! (fmt == "H" || fmt == "I")) 
         return HandleOtherFormats(fmt, arg);

      // Convert argument to a string.
      string result = arg.ToString();

      // If account number is less than 12 characters, pad with leading zeroes.
      if (result.Length < ACCT_LENGTH)
         result = result.PadLeft(ACCT_LENGTH, '0');
      // If account number is more than 12 characters, truncate to 12 characters.
      if (result.Length > ACCT_LENGTH)
         result = result.Substring(0, ACCT_LENGTH);   

      if (fmt.ToUpper() == "I")                    // Integer-only format. 
         return result;
      // Add hyphens for H format specifier.
      else if (fmt.ToUpper() == "H")               // Hyphenated format.
         return result.Substring(0, 5) + "-" + result.Substring(5, 3) + "-" + result.Substring(8);
      // Return string representation of argument for any other formatting code.
      else
         try {
            return HandleOtherFormats(fmt, arg); 
         }
         catch (FormatException e) {
            throw new FormatException(String.Format("The format of '{0}' is invalid.", fmt), e);
         }
   }

   private string HandleOtherFormats(string format, object arg)
   {
      if (arg is IFormattable) 
         return ((IFormattable)arg).ToString(format, CultureInfo.CurrentCulture);
      else if (arg != null)
         return arg.ToString();
      else
         return String.Empty;
   }
}

An instance of the AcctNumberFormat class can then be passed as an argument to a method that provides formatting or parsing services. For example, the following code passes an AcctNumberFormat class to the String..::.Format(IFormatProvider, String, array<Object>[]()[]) method to generate a formatted 12-digit account number.

Imports System.Globalization

Public Enum DaysOfWeek As Long
   Monday = 1
   Tuesday = 2
End Enum

Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim acctNumber As Long, balance As Double 
      Dim wday As DaysOfWeek 
      Dim output As String

      acctNumber = 104254567890
      balance = 16.34
      wday = DaysOfWeek.Monday

      output = String.Format(New AcctNumberFormat(), "On {2}, the balance of account {0:H} was {1:C2}.", acctNumber, balance, wday)
      outputBlock.Text += output + vbCrLf

      wday = DaysOfWeek.Tuesday
      output = String.Format(New AcctNumberFormat(), "On {2}, the balance of account {0:I} was {1:C2}.", acctNumber, balance, wday)
      outputBlock.Text += output + vbCrLf
   End Sub
End Module
' The example displays the following output:
'    On Monday, the balance of account 10425-456-7890 was $16.34.
'    On Tuesday, the balance of account 104254567890 was $16.34.
public enum DaysOfWeek { Monday=1, Tuesday=2 };

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      long acctNumber;
      double balance; 
      DaysOfWeek wday; 
      string output;

      acctNumber = 104254567890;
      balance = 16.34;
      wday = DaysOfWeek.Monday;

      output = String.Format(new AcctNumberFormat(), 
                             "On {2}, the balance of account {0:H} was {1:C2}.", 
                             acctNumber, balance, wday);
      outputBlock.Text += output + "\n";

      wday = DaysOfWeek.Tuesday;
      output = String.Format(new AcctNumberFormat(), 
                             "On {2}, the balance of account {0:I} was {1:C2}.", 
                             acctNumber, balance, wday);
      outputBlock.Text += output + "\n";
   }
}
// The example displays the following output:
//    On Monday, the balance of account 10425-456-7890 was $16.34.
//    On Tuesday, the balance of account 104254567890 was $16.34.

Version Information

Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Platforms

Windows Phone

See Also

Reference

IFormatProvider Interface

System Namespace