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Interfaccia IFormatProvider

Offre un meccanismo per recuperare un oggetto di controllo della formattazione.

Spazio dei nomi: System
Assembly: mscorlib (in mscorlib.dll)

[ComVisibleAttribute(true)] 
public interface IFormatProvider
/** @attribute ComVisibleAttribute(true) */ 
public interface IFormatProvider
ComVisibleAttribute(true) 
public interface IFormatProvider

Alcuni metodi in Common Language Runtime consentono la conversione di un valore verso oppure da una rappresentazione in formato stringa e ricavano un parametro stringa contenente uno o più caratteri, chiamati specificatori di parametro, nei quali è indicato come effettuare la conversione. Se il significato dello specificatore di formato varia secondo la lingua, i caratteri effettivamente utilizzati nella rappresentazione in forma di stringa verranno forniti mediante l'oggetto formattatore.

Mediante una classe o un tipo valore è possibile implementare il metodo GetFormat di questa interfaccia per ottenere un oggetto che fornisca informazioni sul formato o che consenta l'elaborazione per il tipo di implementazione.

L'oggetto IFormatProvider, ad esempio, è implementato da NumberFormatInfo e DateTimeFormatInfo. NumberFormatInfo offre informazioni specifiche della lingua per formattare i numeri dei tipi di dati di base, mentre DateTimeFormatInfo fornisce informazioni specifiche della lingua per formattare i valori di data e ora.

Nell'esempio di codice riportato di seguito viene illustrato l'utilizzo di una classe per l'implementazione dell'interfaccia IFormatProvider e del metodo GetFormat. La classe AnyRadix supporta il codice di formattazione "Ra" e converte un valore Int64 in una stringa di qualsiasi radice specificata tra 2 e 36. GetFormat restituisce un riferimento a se stesso se il parametro Type fa riferimento a una classe che implementa ICustomFormatter; altrimenti, GetFormat restituisce riferimento null (Nothing in Visual Basic).

// Sample for the IFormatProvider interface and
// the IFormatProvider.GetFormat( Type ) method.
using System;

// This class implements the "Ra" formatting code. An instance of this 
// class should be passed to methods requiring an IFormatProvider.
public class AnyRadix : ICustomFormatter, IFormatProvider
{
    // The value to be formatted is returned as a signed string 
    // of digits from the rDigits array. 
    const string radixCode = "Ra";
    private static char[] rDigits = {
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 
        'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 
        'U', 'V', 'W', 'X', 'Y', 'Z' };
        
    // This method returns an object that implements ICustomFormatter 
    // to do the formatting. 
    public object GetFormat( Type argType )
    {
        // Here, the same object (this) is returned, but it would 
        // be possible to return an object of a different type.
        if ( argType == typeof( ICustomFormatter ) )
            return this;
        else
            return null;
    } 
        
    // This method does the formatting only if it recognizes the 
    // format codes. 
    public string Format( string formatString, 
        object argToBeFormatted, IFormatProvider provider )
    {
        // If no format string is provided or the format string cannot 
        // be handled, use IFormattable or standard string processing.
        if( formatString == null || 
            ! formatString.Trim( ).StartsWith( radixCode ) )
        {
            if( argToBeFormatted is IFormattable )
                return ( (IFormattable)argToBeFormatted ).
                    ToString( formatString, provider );
            else
                return argToBeFormatted.ToString( );
        }

        // The formatting is handled here.
        int     digitIndex = 0;
        long    radix;
        long    longToBeFormatted;
        long    longPositive;
        char[ ] outDigits = new char[ 63 ];
            
        // Extract the radix from the format string.
        formatString = formatString.Replace( radixCode, "" );
        try
        {
            radix = Convert.ToInt64( formatString );
        }
        catch( Exception ex )
        {
            throw new ArgumentException( String.Format( 
                "The radix \"{0}\" is invalid.", 
                formatString ), ex );
        }

        // Verify that the radix is in the proper range.
        if( radix <2 || radix > 36 )
            throw new ArgumentException( String.Format( 
                "The radix \"{0}\" is not in the range 2..36.", 
                formatString ) );
            
        // Verify that the argument can be converted to a long integer.
        try
        {
            longToBeFormatted = (long)argToBeFormatted;
        }
        catch( Exception ex )
        {
            throw new ArgumentException( String.Format(
                "The argument \"{0}\" cannot be " +
                "converted to an integer value.", 
                argToBeFormatted ), ex );
        }
            
        // Extract the magnitude for conversion.
        longPositive = Math.Abs( longToBeFormatted );

        // Convert the magnitude to a digit string.
        for( digitIndex = 0; digitIndex <= 64; digitIndex++ )
        {
            if( longPositive == 0 ) break;

            outDigits[ outDigits.Length - digitIndex - 1 ] = 
                rDigits[ longPositive % radix ];
            longPositive /= radix;
        }
            
        // Add a minus sign if the argument is negative.
        if( longToBeFormatted < 0 )
            outDigits[ outDigits.Length - digitIndex++ - 1 ] = 
                '-';

        return new string( outDigits, 
            outDigits.Length - digitIndex, digitIndex );
    } 
} 

class IFormatProviderDemo
{
    static void ConvertToAnyRadix( object argToConvert, 
        string formatStr )
    {
        AnyRadix    provider = new AnyRadix( );
        string      messageStr = 
            String.Format( "{{0:{0}}}", formatStr );

        // Write the first part of the output line.
        Console.Write( "{0,18}  {1,-6}", argToConvert, formatStr );

        // Convert the specified argument using the specified format.
        try
        {
            Console.WriteLine( String.Format( 
                provider, messageStr, argToConvert ) );
        }
        catch( Exception ex )
        {
            // Display the exception without the stack trace.
            int lineEnd = ex.ToString( ).IndexOf( '\n' );
            Console.WriteLine( "{0}\n",
                ex.ToString( ).Substring( 0, lineEnd ) );
        }
    } 
        
    static void Main( )
    {
        long twoToThe32 = 4294967296;
        long fifteenNines = 999999999999999;
            
        Console.WriteLine(
            "This example of the IFormatProvider interface \n" +
            "and the IFormatProvider.GetFormat( Type ) method " +
            "\ngenerates the following output.\n" );
        Console.WriteLine( "{0,18} Format Result", "Number" );
        Console.WriteLine( "{0,18} ------ ------", "------" );
            
        // These are valid conversions.
        ConvertToAnyRadix( twoToThe32, "Ra2" );
        ConvertToAnyRadix( twoToThe32, "Ra5" );
        ConvertToAnyRadix( twoToThe32, "Ra16" );
        ConvertToAnyRadix( twoToThe32, "Ra23" );
        ConvertToAnyRadix( twoToThe32, "Ra36" );
        ConvertToAnyRadix( fifteenNines, "Ra2" );
        ConvertToAnyRadix( fifteenNines, "Ra3" );
        ConvertToAnyRadix( fifteenNines, "Ra8" );
        ConvertToAnyRadix( fifteenNines, "Ra11" );
        ConvertToAnyRadix( fifteenNines, "Ra16" );
        ConvertToAnyRadix( fifteenNines, "Ra23" );
        ConvertToAnyRadix( fifteenNines, "Ra36" );
        ConvertToAnyRadix( fifteenNines, "E16" );
        ConvertToAnyRadix( fifteenNines, "" );
            
        // These are error conditions.
        ConvertToAnyRadix( fifteenNines, "Ra37" );
        ConvertToAnyRadix( "ABCDEFGHIJKLM", "Ra16" );
    } 
} 

/*
This example of the IFormatProvider interface
and the IFormatProvider.GetFormat( Type ) method
generates the following output.

            Number Format Result
            ------ ------ ------
        4294967296  Ra2   100000000000000000000000000000000
        4294967296  Ra5   32244002423141
        4294967296  Ra16  100000000
        4294967296  Ra23  1606K7IC
        4294967296  Ra36  1Z141Z4
   999999999999999  Ra2   11100011010111111010100100110001100111111111111111
   999999999999999  Ra3   11212010201001210101011021212000
   999999999999999  Ra8   34327724461477777
   999999999999999  Ra11  26A6A3689065639
   999999999999999  Ra16  38D7EA4C67FFF
   999999999999999  Ra23  1134DIFHLMM4
   999999999999999  Ra36  9UGXNORJLR
   999999999999999  E16   9.9999999999999900E+014
   999999999999999        999999999999999
   999999999999999  Ra37  System.ArgumentException: The radix "37" is not in th
e range 2..36.

     ABCDEFGHIJKLM  Ra16  System.ArgumentException: The argument "ABCDEFGHIJKLM
" cannot be converted to an integer value. ---> System.InvalidCastException: Sp
ecified cast is not valid.
*/

// Sample for the IFormatProvider interface and
// the IFormatProvider.GetFormat( Type ) method.
import System.*;

// This class implements the "Ra" formatting code. An instance of this
// class should be passed to methods requiring an IFormatProvider.
public class AnyRadix implements ICustomFormatter,IFormatProvider
{
    // The value to be formatted is returned as a signed string 
    // of digits from the rDigits array. 
    private String radixCode = "Ra";
    private static char rDigits[] = {
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 
        'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 
        'U', 'V', 'W', 'X', 'Y', 'Z' };
   
    // This method returns an object that implements ICustomFormatter 
    // to do the formatting. 
    public Object GetFormat(Type argType)
    {
        // Here, the same object (this) is returned, but it would 
        // be possible to return an object of a different type.
        if ( argType.Equals(ICustomFormatter.class.ToType()) ) {
            return this ;
        }
        else {
            return null ;
        }
    } //GetFormat
    
    // This method does the formatting only if it recognizes the 
    // format codes. 
    public String Format(String formatString, Object argToBeFormatted,
                        IFormatProvider provider) 
    {
        // If no format string is provided or the format string cannot 
        // be handled, use IFormattable or standard string processing.
        if(formatString == null||!(formatString.Trim().StartsWith(radixCode))) {
            if ( argToBeFormatted instanceof IFormattable  ) {
                return((IFormattable)(argToBeFormatted)).
                    ToString(formatString,provider);
            }
            else {
                return argToBeFormatted.ToString();
            }
        }

        // The formatting is handled here.
        int digitIndex = 0;
        long radix;
        long longToBeFormatted;
        long longPositive;
        char outDigits[] = new char[63];
      
        // Extract the radix from the format string.
        formatString = formatString.Replace(radixCode, "");
        try {
            radix = Convert.ToInt64(formatString);
        }
        catch(System.Exception  ex) {
            throw new ArgumentException(String.Format(
                "The radix \"{0}\" is invalid.", formatString), ex);
        }
      
        // Verify that the radix is in the proper range.
        if ( radix < 2 || radix > 36  ) {
            throw new ArgumentException(String.Format(
                "The radix \"{0}\" is not in the range 2..36.", formatString));
        }
      
        // Verify that the argument can be converted to a long integer.
        try {
            longToBeFormatted =(long)System.Convert.ToUInt64(argToBeFormatted);
        }
        catch(System.Exception  ex) {
            throw new ArgumentException(String.Format(
                "The argument \"{0}\" cannot be "
                + "converted to an integer value.", argToBeFormatted), ex);
        }
      
        // Extract the magnitude for conversion.
        longPositive = System.Math.Abs(longToBeFormatted);

        // Convert the magnitude to a digit string.
        for(digitIndex = 0;digitIndex <= 64;digitIndex++) {
            if ( longPositive == 0  ) {
                break ;
            }        
            outDigits[outDigits.length - digitIndex - 1] = 
                rDigits[(int)(longPositive % radix)];
            longPositive /= radix;
        }      
        // Add a minus sign if the argument is negative.
        if ( longToBeFormatted < 0  ) {
            outDigits [outDigits.length - digitIndex ++ - 1] = '-';
        }      
        return new String(outDigits, outDigits.length - digitIndex, digitIndex);
    } //Format
} //AnyRadix

class IFormatProviderDemo
{   
    static void ConvertToAnyRadix(Object argToConvert, String formatStr) 
    {
        AnyRadix provider = new AnyRadix();        
        String messageStr = String.Format("{{0:{0}}}", formatStr);
        
        // Write the first part of the output line.
        Console.Write("{0,18}  {1,-6}", argToConvert, formatStr);
        
        // Convert the specified argument using the specified format.
        try {
            Console.WriteLine(String.Format((IFormatProvider)provider,
                messageStr,new Object[]{ argToConvert}));
        }
        catch(System.Exception ex) {
            // Display the exception without the stack trace.
            int lineEnd = ex.ToString().IndexOf('\n');            
            Console.WriteLine("{0}\n", ex.ToString().Substring(0, lineEnd));
        }
    } //ConvertToAnyRadix  
   
    public static void main(String[] args)
    {
        long twoToThe32 = 4294967296L;
        long fifteenNines = 999999999999999L;

        Console.WriteLine(("This example of the IFormatProvider interface \n"
            + "and the IFormatProvider.GetFormat( Type ) method "
            + "\ngenerates the following output.\n"));
        Console.WriteLine("{0,18} Format Result", "Number");
        Console.WriteLine("{0,18} ------ ------", "------");

        // These are valid conversions.
        ConvertToAnyRadix(((System.UInt64 )(twoToThe32)), "Ra2");
        ConvertToAnyRadix(((System.UInt64)(twoToThe32)), "Ra5");
        ConvertToAnyRadix(((System.UInt64)(twoToThe32)), "Ra16");
        ConvertToAnyRadix(((System.UInt64)(twoToThe32)), "Ra23");
        ConvertToAnyRadix(((System.UInt64)(twoToThe32)), "Ra36");
        ConvertToAnyRadix(((System.UInt64)(fifteenNines)), "Ra2");
        ConvertToAnyRadix(((System.UInt64)(fifteenNines)), "Ra3");
        ConvertToAnyRadix(((System.UInt64)(fifteenNines)), "Ra8");
        ConvertToAnyRadix(((System.UInt64)(fifteenNines)), "Ra11");
        ConvertToAnyRadix(((System.UInt64)(fifteenNines)), "Ra16");
        ConvertToAnyRadix(((System.UInt64)(fifteenNines)), "Ra23");
        ConvertToAnyRadix(((System.UInt64)(fifteenNines)), "Ra36");
        ConvertToAnyRadix(((System.UInt64)(fifteenNines)), "E16");
        ConvertToAnyRadix(((System.UInt64)(fifteenNines)), "");

        // These are error conditions.
        ConvertToAnyRadix(((System.UInt64)(fifteenNines)), "Ra37");
        ConvertToAnyRadix("ABCDEFGHIJKLM", "Ra16");
    } //main
} //IFormatProviderDemo

/*
This example of the IFormatProvider interface
and the IFormatProvider.GetFormat( Type ) method
generates the following output.

            Number Format Result
            ------ ------ ------
        4294967296  Ra2   100000000000000000000000000000000
        4294967296  Ra5   32244002423141
        4294967296  Ra16  100000000
        4294967296  Ra23  1606K7IC
        4294967296  Ra36  1Z141Z4
   999999999999999  Ra2   11100011010111111010100100110001100111111111111111
   999999999999999  Ra3   11212010201001210101011021212000
   999999999999999  Ra8   34327724461477777
   999999999999999  Ra11  26A6A3689065639
   999999999999999  Ra16  38D7EA4C67FFF
   999999999999999  Ra23  1134DIFHLMM4
   999999999999999  Ra36  9UGXNORJLR
   999999999999999  E16   9.9999999999999900E+014
   999999999999999        999999999999999
   999999999999999  Ra37  System.ArgumentException: The radix "37" is not in th
e range 2..36.

     ABCDEFGHIJKLM  Ra16  System.ArgumentException: The argument "ABCDEFGHIJKLM"
 cannot be converted to an integer value. ---> System.FormatException: Input str
ing was not in a correct format.
*/

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile per Pocket PC, Windows Mobile per Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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.NET Framework

Supportato in: 2.0 1.1 1.0

.NET Compact Framework

Supportato in: 2.0 1.0
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