發行項
11/18/2011

UInt16.TryParse Method (String, NumberStyles, IFormatProvider, UInt16%)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Updated: August 2009

Tries to convert the string representation of a number in a specified style and culture-specific format to its 16-bit unsigned integer equivalent. A return value indicates whether the conversion succeeded or failed.

This API is not CLS-compliant. The CLS-compliant alternative is TryParse(String, Int32%).

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

Syntax

'Declaration
<CLSCompliantAttribute(False)> _
Public Shared Function TryParse ( _
    s As String, _
    style As NumberStyles, _
    provider As IFormatProvider, _
    <OutAttribute> ByRef result As UShort _
) As Boolean

[CLSCompliantAttribute(false)]
public static bool TryParse(
    string s,
    NumberStyles style,
    IFormatProvider provider,
    out ushort result
)

Parameters

s
Type: System.String
A string that represents the number to convert. The string is interpreted by using the style specified by the style parameter.

style
Type: System.Globalization.NumberStyles
A bitwise combination of enumeration values that indicates the permitted format of s. A typical value to specify is NumberStyles.Integer.

provider
Type: System.IFormatProvider
An object that supplies culture-specific formatting information about s.

result
Type: System.UInt16%
When this method returns, contains the 16-bit unsigned integer value equivalent to the number contained in s, if the conversion succeeded, or zero if the conversion failed. The conversion fails if the s parameter is nulla null reference (Nothing in Visual Basic), is not in a format compliant with style, or represents a number less than UInt16.MinValue or greater than UInt16.MaxValue. This parameter is passed uninitialized.

Return Value

Type: System.Boolean
true if s was converted successfully; otherwise, false.

Exceptions

Exception	Condition
ArgumentException	style is not a NumberStyles value. -or- style is not a combination of NumberStyles.AllowHexSpecifier and NumberStyles.HexNumber values.

ArgumentException

style is not a NumberStyles value.

-or-

style is not a combination of NumberStyles.AllowHexSpecifier and NumberStyles.HexNumber values.

Remarks

The TryParse(String, NumberStyles, IFormatProvider, UInt16%) method is like the Parse(String, NumberStyles, IFormatProvider) method, except that it does not throw an exception if the conversion fails. This method eliminates the need to use exception handling to test for a FormatException if s is invalid and cannot be parsed successfully..

The style parameter defines the style elements (such as white space or a positive or negative sign) that are allowed in the s parameter for the parse operation to succeed. It must be a combination of bit flags from the NumberStyles enumeration. Depending on the value of style, the s parameter may include the following elements:

[ws][$][sign][digits,]digits[.fractional_digits][E[sign]exponential_digits][ws]

Items in square brackets ([ and ]) are optional. Or, if the style parameter includes AllowHexSpecifier, the s parameter may include the following elements:

[ws]hexdigits[ws]

The following table describes each element.

ws
Optional white space. White space can appear at the start of s if style includes the NumberStyles.AllowLeadingWhite flag, or at the end of s if style includes the NumberStyles.AllowTrailingWhite flag.
$
A culture-specific currency symbol. Its position in the string is defined by the CurrencyPositivePattern property of the NumberFormatInfo object returned by the GetFormat method of the provider parameter. The currency symbol can appear in s if style includes the NumberStyles.AllowCurrencySymbol flag.
sign
An optional sign. The sign can appear at the start of s if style includes the NumberStyles.AllowLeadingSign flag, and it can appear at the end of s if style includes the NumberStyles.AllowTrailingSign flag. Parentheses can be used in s to indicate a negative value if style includes the NumberStyles.AllowParentheses flag. However, if the negative sign is present, s can only represent the value zero for the parse operation to succeed.
digits
A sequence of digits from 0 through 9.
,
A culture-specific group separator. The group separator of the culture specified by provider can appear in s if style includes the NumberStyles.AllowThousands flag.
.
A culture-specific decimal point symbol. The decimal point symbol of the culture specified by provider can appear in s if style includes the NumberStyles.AllowDecimalPoint flag.
fractional_digits
One or more occurrences of the digit 0. Fractional digits can appear in s only if style includes the NumberStyles.AllowDecimalPoint flag.
E
The "e" or "E" character, which indicates that the value is represented in exponential (scientific) notation. The s parameter can represent a number in exponential notation if style includes the NumberStyles.AllowExponent flag.
exponential_digits
A sequence of digits from 0 through 9. The s parameter can represent a number in exponential notation if style includes the NumberStyles.AllowExponent flag.
hexdigits
A sequence of hexadecimal digits from 0 through f, or 0 through F.

A string with decimal digits only (which corresponds to the NumberStyles.None flag) always parses successfully. Most of the remaining NumberStyles members control elements that may be present, but are not required to be present, in this input string. The following table indicates how individual NumberStyles members affect the elements that may be present in s.

Non-composite NumberStyles values	Elements permitted in value in addition to digits
None	Decimal digits only.
AllowDecimalPoint	The decimal point (.) and fractional_digits elements. However, fractional_digits must consist of only one or more 0 digits, or the method returns false.
AllowExponent	The "e" or "E" character, which indicates exponential notation, along with exponential_digits. If s represents a number in exponential notation, it cannot have a non-zero, fractional component.
AllowLeadingWhite	The ws element at the start of s.
AllowTrailingWhite	The ws element at the end of s.
AllowLeadingSign	The sign element before digits.
AllowTrailingSign	The sign element after digits.
AllowParentheses	The sign element in the form of parentheses enclosing a zero numeric value.
AllowThousands	The group separator (,) element.
AllowCurrencySymbol	The currency ($) element.
Currency	All elements. However, s cannot represent a hexadecimal number or a number in exponential notation.
Float	The ws element at the start or end of s, sign at the start of s, and the decimal point (.) symbol. The s parameter can also use exponential notation.
Number	The ws, sign, group separator (,), and decimal point (.) elements.
Any	All elements. However, s cannot represent a hexadecimal number.

If the NumberStyles.AllowHexSpecifier flag is used, s must be a hexadecimal value. The only other flags that can be present in style are NumberStyles.AllowLeadingWhite and NumberStyles.AllowTrailingWhite. (The NumberStyles enumeration has a composite style, HexNumber, that includes both white-space flags.)

Note:
If s is the string representation of a hexadecimal number, it cannot be preceded by any decoration (such as 0x or &h) that differentiates it as a hexadecimal number. This causes the conversion to fail.

The provider parameter is an IFormatProvider implementation. Its GetFormat method returns a NumberFormatInfo object that provides culture-specific information about the format of s. The provider parameter can be any one of the following:

A CultureInfo object that represents the culture that supplies formatting information. Its GetFormat method returns the NumberFormatInfo object that provides numeric formatting information for that culture.
A NumberFormatInfo object that provides numeric formatting information. (Its implementation of GetFormat just returns itself.)
A custom object that implements IFormatProvider. Its GetFormat method instantiates and returns the NumberFormatInfo object that provides formatting information.

If provider is nulla null reference (Nothing in Visual Basic), the NumberFormatInfo object for the current culture is used.

Examples

The following example calls the TryParse(String, NumberStyles, IFormatProvider, UInt16%) method with a number of different strings and NumberStyles values.

Imports System.Globalization

Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim numericString As String
      Dim styles As NumberStyles

      numericString = "10603"
      styles = NumberStyles.Integer
      CallTryParse(outputBlock, numericString, styles)

      numericString = "-10603"
      styles = NumberStyles.None
      CallTryParse(outputBlock, numericString, styles)

      numericString = "29103.00"
      styles = NumberStyles.Integer Or NumberStyles.AllowDecimalPoint
      CallTryParse(outputBlock, numericString, styles)

      numericString = "10345.72"
      styles = NumberStyles.Integer Or NumberStyles.AllowDecimalPoint
      CallTryParse(outputBlock, numericString, styles)

      numericString = "2210E-01"
      styles = NumberStyles.Integer Or NumberStyles.AllowExponent
      CallTryParse(outputBlock, numericString, styles)

      numericString = "9112E-01"
      CallTryParse(outputBlock, numericString, styles)

      numericString = "312E01"
      CallTryParse(outputBlock, numericString, styles)

      numericString = "FFC8"
      CallTryParse(outputBlock, numericString, NumberStyles.HexNumber)

      numericString = "0x8F8C"
      CallTryParse(outputBlock, numericString, NumberStyles.HexNumber)
   End Sub

   Private Sub CallTryParse(ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal stringToConvert As String, ByVal styles As NumberStyles)
      Dim number As UShort
      Dim result As Boolean = UInt16.TryParse(stringToConvert, styles, _
                                              CultureInfo.InvariantCulture, number)
      If result Then
         outputBlock.Text += String.Format("Converted '{0}' to {1}.", stringToConvert, number) & vbCrLf
      Else
         outputBlock.Text += String.Format("Attempted conversion of '{0}' failed.", _
                           Convert.ToString(stringToConvert)) & vbCrLf
      End If
   End Sub
End Module
' The example displays the following output:
'       Converted '10603' to 10603.
'       Attempted conversion of '-10603' failed.
'       Converted '29103.00' to 29103.
'       Attempted conversion of '10345.72' failed.
'       Converted '2210E-01' to 221.
'       Attempted conversion of '9112E-01' failed.
'       Converted '312E01' to 3120.
'       Converted 'FFC8' to 65480.
'       Attempted conversion of '0x8F8C' failed.

using System;
using System.Globalization;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string numericString;
      NumberStyles styles;

      numericString = "10603";
      styles = NumberStyles.Integer;
      CallTryParse(outputBlock, numericString, styles);

      numericString = "-10603";
      styles = NumberStyles.None;
      CallTryParse(outputBlock, numericString, styles);

      numericString = "29103.00";
      styles = NumberStyles.Integer | NumberStyles.AllowDecimalPoint;
      CallTryParse(outputBlock, numericString, styles);

      numericString = "10345.72";
      styles = NumberStyles.Integer | NumberStyles.AllowDecimalPoint;
      CallTryParse(outputBlock, numericString, styles);

      numericString = "2210E-01";
      styles = NumberStyles.Integer | NumberStyles.AllowExponent;
      CallTryParse(outputBlock, numericString, styles);

      numericString = "9112E-01";
      CallTryParse(outputBlock, numericString, styles);

      numericString = "312E01";
      CallTryParse(outputBlock, numericString, styles);

      numericString = "FFC8";
      CallTryParse(outputBlock, numericString, NumberStyles.HexNumber);

      numericString = "0x8F8C";
      CallTryParse(outputBlock, numericString, NumberStyles.HexNumber);
   }

   private static void CallTryParse(System.Windows.Controls.TextBlock outputBlock, string stringToConvert, NumberStyles styles)
   {
      ushort number;
      bool result = UInt16.TryParse(stringToConvert, styles,
                                   CultureInfo.InvariantCulture, out number);
      if (result)
         outputBlock.Text += String.Format("Converted '{0}' to {1}.", stringToConvert, number) + "\n";
      else
         outputBlock.Text += String.Format("Attempted conversion of '{0}' failed.",
                           Convert.ToString(stringToConvert)) + "\n";
   }
}
// The example displays the following output:
//       Converted '10603' to 10603.
//       Attempted conversion of '-10603' failed.
//       Converted '29103.00' to 29103.
//       Attempted conversion of '10345.72' failed.
//       Converted '2210E-01' to 221.
//       Attempted conversion of '9112E-01' failed.
//       Converted '312E01' to 3120.
//       Converted 'FFC8' to 65480.
//       Attempted conversion of '0x8F8C' failed.

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Change History

Date	History	Reason
August 2009	Revised extensively.	Information enhancement.

共用方式為