String.IsNullOrEmpty(String) String.IsNullOrEmpty(String) String.IsNullOrEmpty(String) String.IsNullOrEmpty(String) Method

Definição

Indica se a cadeia de caracteres especificada é null ou uma cadeia de caracteres vazia ("").Indicates whether the specified string is null or an empty string ("").

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

Parâmetros

value
String String String String

A cadeia de caracteres a ser testada.The string to test.

Retornos

true se o parâmetro value for null ou uma cadeia de caracteres vazia (""); caso contrário, false.true if the value parameter is null or an empty string (""); otherwise, false.

Exemplos

O exemplo a seguir examina três Strings e determina se cada cadeia de caracteres tem um valor, é uma cadeia de caracteres nullvazia ou é.The following example examines three strings and determines whether each string has a value, is an empty string, or is null.

using namespace System;
String^ Test( String^ s )
{
   if (String::IsNullOrEmpty(s))
      return "is null or empty";
   else
      return String::Format( "(\"{0}\") is neither null nor empty", s );
}

int main()
{
   String^ s1 = "abcd";
   String^ s2 = "";
   String^ s3 = nullptr;
   Console::WriteLine( "String s1 {0}.", Test( s1 ) );
   Console::WriteLine( "String s2 {0}.", Test( s2 ) );
   Console::WriteLine( "String s3 {0}.", Test( s3 ) );
}
// The example displays the following output:
//       String s1 ("abcd") is neither null nor empty.
//       String s2 is null or empty.
//       String s3 is null or empty.
string s1 = "abcd";
string s2 = "";
string s3 = null;

Console.WriteLine("String s1 {0}.", Test(s1));
Console.WriteLine("String s2 {0}.", Test(s2));
Console.WriteLine("String s3 {0}.", Test(s3));

String Test(string s)
{
if (String.IsNullOrEmpty(s)) 
    return "is null or empty";
else
    return String.Format("(\"{0}\") is neither null nor empty", s);
}

// The example displays the following output:
//       String s1 ("abcd") is neither null nor empty.
//       String s2 is null or empty.
//       String s3 is null or empty.
Class Sample
   Public Shared Sub Main()
      Dim s1 As String = "abcd"
      Dim s2 As String = ""
      Dim s3 As String = Nothing
      
      Console.WriteLine("String s1 {0}.", Test(s1))
      Console.WriteLine("String s2 {0}.", Test(s2))
      Console.WriteLine("String s3 {0}.", Test(s3))
   End Sub
   
   Public Shared Function Test(s As String) As String
      If String.IsNullOrEmpty(s) Then
         Return "is null or empty"
      Else
         Return String.Format("(""{0}"") is neither null nor empty", s)
      End If
   End Function 
End Class  
' The example displays the following output:
'       String s1 ("abcd") is neither null nor empty.
'       String s2 is null or empty.
'       String s3 is null or empty.

Comentários

IsNullOrEmptyé um método de conveniência que permite que você teste simultaneamente se String um null é ou seu valor String.Empty.IsNullOrEmpty is a convenience method that enables you to simultaneously test whether a String is null or its value is String.Empty. É equivalente ao seguinte código:It is equivalent to the following code:

result = s == nullptr || s == String::Empty;
bool TestForNullOrEmpty(string s)
{
    bool result;
    result = s == null || s == string.Empty;
    return result;
}

string s1 = null;
string s2 = "";
Console.WriteLine(TestForNullOrEmpty(s1));
Console.WriteLine(TestForNullOrEmpty(s2));
result = s Is Nothing OrElse s = String.Empty

Você pode usar o IsNullOrWhiteSpace método para testar se uma cadeia de nullcaracteres é, seu String.Emptyvalor é ou se ela consiste apenas em caracteres de espaço em branco.You can use the IsNullOrWhiteSpace method to test whether a string is null, its value is String.Empty, or it consists only of white-space characters.

O que é uma cadeia de caracteres nula?What is a null string?

Uma cadeia de null caracteres é se não tiver sido atribuído um valor ( C++ in e Visual Basic) ou se tiver explicitamente atribuído um valor de null.A string is null if it has not been assigned a value (in C++ and Visual Basic) or if it has explicitly been assigned a value of null. Embora o recurso de formatação composta possa manipular normalmente uma cadeia de caracteres nula, como mostra o exemplo a seguir, tentar chamar um se seus membros NullReferenceExceptionlançam um.Although the composite formatting feature can gracefully handle a null string, as the following example shows, attempting to call one if its members throws a NullReferenceException.

using namespace System;

void main()
{
   String^ s;
  
   Console::WriteLine("The value of the string is '{0}'", s);

   try {
      Console::WriteLine("String length is {0}", s->Length);
   }
   catch (NullReferenceException^ e) {
      Console::WriteLine(e->Message);
   }   
}
// The example displays the following output:
//     The value of the string is ''
//     Object reference not set to an instance of an object.
String s = null;

Console.WriteLine("The value of the string is '{0}'", s);

try 
{
    Console.WriteLine("String length is {0}", s.Length);
}
catch (NullReferenceException e) 
{
    Console.WriteLine(e.Message);
}

// The example displays the following output:
//     The value of the string is ''
//     Object reference not set to an instance of an object.
Module Example
   Public Sub Main()
      Dim s As String

      Console.WriteLine("The value of the string is '{0}'", s)

      Try 
         Console.WriteLine("String length is {0}", s.Length)
      Catch e As NullReferenceException
         Console.WriteLine(e.Message)
      End Try   
   End Sub
End Module
' The example displays the following output:
'     The value of the string is ''
'     Object reference not set to an instance of an object.

O que é uma cadeia de caracteres vazia?What is an empty string?

Uma cadeia de caracteres estará vazia se for explicitamente atribuída uma cadeia de caracteres vazia (" String.Empty") ou.A string is empty if it is explicitly assigned an empty string ("") or String.Empty. Uma cadeia de caracteres vazia Length tem um de 0.An empty string has a Length of 0. O exemplo a seguir cria uma cadeia de caracteres vazia e exibe seu valor e seu comprimento.The following example creates an empty string and displays its value and its length.

String^ s = "";
Console::WriteLine("The length of '{0}' is {1}.", s, s->Length);
// The example displays the following output:
//       The length of '' is 0.      
String s = "";
Console.WriteLine("The length of '{0}' is {1}.", s, s.Length);

// The example displays the following output:
//       The length of '' is 0.      
Dim s As String = ""
Console.WriteLine("The length of '{0}' is {1}.", s, s.Length)
' The example displays the following output:
'        The length of '' is 0.      

Aplica-se a

Veja também