String.IsNullOrWhiteSpace(String) 方法

定義

命名空間:
System
組件:
System.Runtime.dll
組件:
mscorlib.dll, System.Runtime.dll
組件:
mscorlib.dll
組件:
netstandard.dll

表示指定的字串是否為 null、空白，或只由空白字元組成的字串。Indicates whether a specified string is null, empty, or consists only of white-space characters.

public:
 static bool IsNullOrWhiteSpace(System::String ^ value);
public static bool IsNullOrWhiteSpace (string value);
public static bool IsNullOrWhiteSpace (string? value);
static member IsNullOrWhiteSpace : string -> bool
Public Shared Function IsNullOrWhiteSpace (value As String) As Boolean

參數

value
String

要測試的字串。The string to test.

傳回

Boolean

如果 true 參數是 value 或 null，或者 Empty 完全由空白字元組成，則為 value。true if the value parameter is null or Empty, or if value consists exclusively of white-space characters.

範例

下列範例會建立字串陣列，然後將陣列的每個元素傳遞給 IsNullOrWhiteSpace 方法。The following example creates a string array, and then passes each element of the array to the IsNullOrWhiteSpace method.

using System;

public class Example
{
   public static void Main()
   {
      string[] values = { null, String.Empty, "ABCDE", 
                          new String(' ', 20), "  \t   ", 
                          new String('\u2000', 10) };
      foreach (string value in values)
         Console.WriteLine(String.IsNullOrWhiteSpace(value));
   }
}
// The example displays the following output:
//       True
//       True
//       False
//       True
//       True
//       True

Module Example
   Public Sub Main()
      Dim values() As String = { Nothing, String.Empty, "ABCDE", 
                                 New String(" "c, 20), "  " + vbTab + "   ", 
                                 New String(ChrW(&h2000), 10) }
      For Each value As String In values
         Console.WriteLine(String.IsNullOrWhiteSpace(value))
      Next
   End Sub
End Module
' The example displays the following output:
'       True
'       True
'       False
'       True
'       True
'       True

備註

IsNullOrWhiteSpace 是很方便的方法，類似于下列程式碼，不同之處在于它會提供較佳的效能：IsNullOrWhiteSpace is a convenience method that is similar to the following code, except that it offers superior performance:

return String.IsNullOrEmpty(value) || value.Trim().Length == 0;

Return String.IsNullOrEmpty(value) OrElse value.Trim().Length = 0

空白字元是由 Unicode 標準所定義。White-space characters are defined by the Unicode standard. IsNullOrWhiteSpace方法 true 會在傳遞至 Char.IsWhiteSpace 方法做為空白字元時，解讀傳回值的任何字元。The IsNullOrWhiteSpace method interprets any character that returns a value of true when it is passed to the Char.IsWhiteSpace method as a white-space character.

適用於

另請參閱