关于asp.net String.IsNullOrEmpty
对于asp.net String.IsNullOrEmpty你了解多少呢？我们在学习ASP.NET的时候掌握String.IsNullOrEmpty是非常重要的，那么下面我们就一起去看看关于asp.net String.IsNullOrEmpty的知识。
此方法在 .NET Framework 2.0 版中是新增的。
指示指定的 String 对象是 空引用（在 Visual Basic 中为 Nothing） 还是 Empty 字符串。
这个方法在VB，VB.Net, C#,C++,JScript,J#中都有，很好很强大的一个方法。
String.Empty 字段
表示空字符串。此字段为只读。
命名空间:System
程序集:mscorlib（在 mscorlib.dll 中）
语法
Visual Basic（声明）
Public Shared ReadOnly Empty As String
Visual Basic（用法）
Dim value As String
value = String.Empty
C#
public static readonly string Empty
C++
public:
static initonly String^ Empty
J#
public static final String Empty
JScript
public static final var Empty : String
备注
此字段的值为零长度字符串 ""。
示例
下面的代码示例演示如何使用 Empty 字段。
在第一个示例中，如果另一个字段的值为 空引用（在 Visual Basic 中为 Nothing），则 Empty 字符串作为默认值返回。
Visual Basic 复制代码
Dim myBinding As DataBinding = DataBindings("Text")
If Not (myBinding Is Nothing) Then
Return myBinding.Expression
End If
Return [String].Empty
End Get
C# 复制代码
DataBinding myBinding = DataBindings["Text"];
if (myBinding != null)
{
return myBinding.Expression;
}
return String.Empty;
C++ 复制代码
DataBinding^ myBinding = DataBindings[ "Text" ];
if ( myBinding != nullptr )
{
return myBinding->Expression;
}
return String::Empty;
J# 复制代码
DataBinding myBinding = get_DataBindings().get_Item("Text");
if (myBinding != null) {
return myBinding.get_Expression();
}
return("");
在第二个示例中，Compare 中使用了 Empty 字符串来测试子字符串。
Visual Basic 复制代码
Dim myString As String = "abc"
Dim test1 As Boolean = String.Compare(myString.Substring(2, 1), "c") = 0 ' This is true.
myString.Substring(3, 1) ' This throws ArgumentOutOfRangeException.
Dim test2 As Boolean = String.Compare(myString.Substring(3, 0), String.Empty) = 0 ' This is true.
C# 复制代码
String myString = "abc";
bool test1 = String.Compare(myString.Substring(2, 1), "c") == 0; // This is true.
myString.Substring(3, 1); // This throws ArgumentOutOfRangeException.
bool test2 = String.Compare(myString.Substring(3, 0), String.Empty) == 0; // This is true.
C++ 复制代码
String^ myString = "abc";
bool test1 = String::Compare( myString->Substring( 2, 1 ), "c" ) == 0; // This is true.
myString->Substring( 3, 1 ); // This throws ArgumentOutOfRangeException.
bool test2 = String::Compare( myString->Substring( 3, 0 ), String::Empty ) == 0; // This is true.
J# 复制代码
String myString = "abc";
// This is true.
boolean test1 = String.Compare(myString.Substring(2, 1), "c") == 0;
myString.Substring(3, 1); // This throws ArgumentOutOfRangeException.
// This is true.
boolean test2 = String.Compare(myString.Substring(3, 0), " ") == 0;
JScript 复制代码
var myString : String = "abc";
var test1 : boolean = String.Compare(myString.Substring(2, 1), "c") == 0; // This is true.
myString.Substring(3, 1); // This throws ArgumentOutOfRangeException.
var test2 : boolean = String.Compare(myString.Substring(3, 0), String.Empty) == 0; // This is true.
在第三个示例中，XPathNavigator 对象的决策块中使用了 Empty 字符串来作出有关 XML 分析的决策。
Visual Basic 复制代码
public shared sub RecursiveWalk(nav as XPathNavigator)
select case nav.NodeType
case XPathNodeType.Element
if (nav.Prefix=String.Empty)
Console.WriteLine("", nav.LocalName)
else
Console.Write("", nav.Prefix, nav.LocalName)
Console.WriteLine(" "+ nav.NamespaceURI)
end if
case XPathNodeType.Text
Console.WriteLine(" " + nav.Value)
end select
if ( nav.MoveToFirstChild() )
do
RecursiveWalk(nav)
loop while ( nav.MoveToNext() )
nav.MoveToParent()
if (nav.NodeType = XPathNodeType.Element)
Console.WriteLine("{0}>", nav.Name)
end if
end if
end sub
C# 复制代码
public static void RecursiveWalk(XPathNavigator nav)
{
switch (nav.NodeType){
case XPathNodeType.Element:
if (nav.Prefix==String.Empty)
Console.WriteLine("", nav.LocalName);
else
Console.Write("", nav.Prefix, nav.LocalName);
Console.WriteLine("\t"+ nav.NamespaceURI);
break;
case XPathNodeType.Text:
Console.WriteLine("\t" + nav.Value);
break;
}
if ( nav.MoveToFirstChild() )
{
do{
RecursiveWalk(nav);
} while ( nav.MoveToNext() );
nav.MoveToParent();
if (nav.NodeType == XPathNodeType.Element)
Console.WriteLine("{0}>", nav.Name);
}
}
C++ 复制代码
static void RecursiveWalk( XPathNavigator^ nav )
{
switch ( nav->NodeType )
{
case XPathNodeType::Element:
if ( nav->Prefix == String::Empty )
Console::WriteLine( "", nav->LocalName );
else
Console::Write( "", nav->Prefix, nav->LocalName );
Console::WriteLine( "\t {0}", nav->NamespaceURI );
break;
case XPathNodeType::Text:
Console::WriteLine( "\t {0}", nav->Value );
break;
}
if ( nav->MoveToFirstChild() )
{
do
{
RecursiveWalk( nav );
}
while ( nav->MoveToNext() );
nav->MoveToParent();
if ( nav->NodeType == XPathNodeType::Element )
Console::WriteLine( " {0}>", nav->Name );
}
}
J# 复制代码
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