String.IsNullOrEmpty(String) 方法
重要
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表示指定的字串是否為 null 或空字串 ("")。
public:
static bool IsNullOrEmpty(System::String ^ value);C#
public static bool IsNullOrEmpty(string value);C#
public static bool IsNullOrEmpty(string? value);static member IsNullOrEmpty : string -> boolPublic Shared Function IsNullOrEmpty (value As String) As Boolean- value
- String
要測試的字串。
如果 true 參數為 value 或空字串 ("")，則為 null，否則為 false。
下列範例會檢查三個字串，並判斷每個字串是否有值、是空字串或 。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.
C#
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.
let test (s: string): string =
if String.IsNullOrEmpty(s)
then "is null or empty"
else $"(\"{s}\") is neither null nor empty"
let s1 = "abcd"
let s2 = ""
let s3 = null
printfn "String s1 %s" (test s1)
printfn "String s2 %s" (test s2)
printfn "String s2 %s" (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.
如需此 API 的詳細資訊，請參閱 String.IsNullOrEmpty 的補充 API 備註。
| 產品 | 版本 |
|---|---|
| .NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9, 10 |
| .NET Framework | 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
| .NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1 |
| UWP | 10.0 |
