XAttribute.Value Properti

Definisi

Ruang nama:

System.Xml.Linq

Rakitan:

System.Xml.XDocument.dll

Sumber:

XAttribute.cs

Mendapatkan atau menetapkan nilai atribut ini.

public:
 property System::String ^ Value { System::String ^ get(); void set(System::String ^ value); };

public string Value { get; set; }

member this.Value : string with get, set

Public Property Value As String

Nilai Properti

String

yang String berisi nilai atribut ini.

Pengecualian

ArgumentNullException

Saat mengatur, value adalah null.

Contoh

Contoh berikut membuat elemen dengan atribut . Kemudian mengambil nilai atribut, lalu mengaturnya.

Perhatikan bahwa contoh Visual Basic menggunakan properti atribut XML.

XElement root = new XElement("Root",  
    new XAttribute("Att", "content")  
);  
XAttribute att = root.FirstAttribute;  
Console.WriteLine(att.Value);  
att.Value = "new text";  
Console.WriteLine(att.Value);  

Dim root As XElement = <Root Att="content"/>  
Console.WriteLine(root.@Att)  
root.@Att = "new text"  
Console.WriteLine(root.@Att)  

Contoh ini mencetak output berikut:

content  
new text  

Contoh berikut menunjukkan manfaat menggunakan operator konversi eksplisit untuk mendapatkan nilai atribut yang mungkin tidak ada:

XElement root = new XElement("Root",  
    new XAttribute("Att1", "attribute 1 content"),  
    new XAttribute("Att2", "2")  
);  

// The following assignments demonstrate why it is easier to use  
// casting when the attribute might or might not exist.  

string c1 = (string)root.Attribute("Att1");  
Console.WriteLine("c1:{0}", c1 == null ? "attribute does not exist" : c1);  

int? c2 = (int?)root.Attribute("Att2");  
Console.WriteLine("c2:{0}", c2 == null ? "attribute does not exist" : c2.ToString());  

string c3 = (string)root.Attribute("Att3");  
Console.WriteLine("c3:{0}", c3 == null ? "attribute does not exist" : c3);  

int? c4 = (int?)root.Attribute("Att4");  
Console.WriteLine("c4:{0}", c4 == null ? "attribute does not exist" : c4.ToString());  

Console.WriteLine();  

// The following assignments show the necessary code when using  
// the value property when the attribute might or might not exist.  

XAttribute att1 = root.Attribute("Att1");  
string v1;  
if (att1 == null)  
    v1 = null;  
else  
    v1 = att1.Value;  
Console.WriteLine("v1:{0}", v1 == null ? "attribute does not exist" : v1);  

XAttribute att2 = root.Attribute("Att2");  
int? v2;  
if (att2 == null)  
    v2 = null;  
else  
    v2 = Int32.Parse(att2.Value);  
Console.WriteLine("v2:{0}", v2 == null ? "attribute does not exist" : v2.ToString());  

XAttribute att3 = root.Attribute("Att3");  
string v3;  
if (att3 == null)  
    v3 = null;  
else  
    v3 = att3.Value;  
Console.WriteLine("v3:{0}", v3 == null ? "attribute does not exist" : v3);  

XAttribute att4 = root.Attribute("Att4");  
int? v4;  
if (att4 == null)  
    v4 = null;  
else  
    v4 = Int32.Parse(att4.Value);  
Console.WriteLine("v4:{0}", v4 == null ? "attribute does not exist" : v4.ToString());  

Dim root As XElement = <Root Att1="attribute 1 content" Att2="2"/>  

' The following assignments demonstrate why it is easier to use  
' casting when the attribute might or might not exist.  

Dim c1 As String = CStr(root.Attribute("Att1"))  
Console.WriteLine("c1:{0}", IIf(c1 Is Nothing, "attribute does not exist", c1))  

Dim c2 As Nullable(Of Integer) = CType(root.Attribute("Att2"), Nullable(Of Integer))  
Console.WriteLine("c2:{0}", IIf(c2.HasValue, c2, "attribute does not exist"))  

Dim c3 As String = CStr(root.Attribute("Att3"))  
Console.WriteLine("c3:{0}", IIf(c3 Is Nothing, "attribute does not exist", c3))  

Dim c4 As Nullable(Of Integer) = CType(root.Attribute("Att4"), Nullable(Of Integer))  
Console.WriteLine("c4:{0}", IIf(c4.HasValue, c4, "attribute does not exist"))  

Console.WriteLine()  

' The following assignments show the necessary code when using  
' the value property when the attribute might or might not exist.  

Dim att1 As XAttribute = root.Attribute("Att1")  
Dim v1 As String  
If att1 Is Nothing Then  
    v1 = Nothing  
Else  
    v1 = att1.Value  
End If  

Console.WriteLine("v1:{0}", IIf(v1 Is Nothing, "attribute does not exist", v1))  

Dim att2 As XAttribute = root.Attribute("Att2")  
Dim v2 As Nullable(Of Integer)  
If att2 Is Nothing Then  
    v2 = Nothing  
Else  
    v2 = Int32.Parse(att2.Value)  
End If  

Console.WriteLine("v2:{0}", IIf(v2.HasValue, v2, "attribute does not exist"))  

Dim att3 As XAttribute = root.Attribute("Att3")  
Dim v3 As String  
If att3 Is Nothing Then  
    v3 = Nothing  
Else  
    v3 = att3.Value  
End If  

Console.WriteLine("v3:{0}", IIf(v3 Is Nothing, "attribute does not exist", v3))  

Dim att4 As XAttribute = root.Attribute("Att4")  
Dim v4 As Nullable(Of Integer)  
If att4 Is Nothing Then  
    v4 = Nothing  
Else  
    v4 = Int32.Parse(att4.Value)  
End If  

Console.WriteLine("v4:{0}", IIf(v4.HasValue, v4, "attribute does not exist"))  

Contoh ini mencetak output berikut:

c1:attribute 1 content  
c2:2  
c3:attribute does not exist  
c4:attribute does not exist  

v1:attribute 1 content  
v2:2  
v3:attribute does not exist  
v4:attribute does not exist  

Keterangan

Anda dapat menggunakan properti ini untuk mendapatkan atau mengatur nilai atribut.

Mengatur properti ini akan meningkatkan Changed peristiwa dan Changing .

Jika Anda mendapatkan nilai dan atribut mungkin tidak ada, lebih mudah untuk menggunakan operator konversi eksplisit, dan menetapkan atribut ke jenis nullable seperti string atau Nullable<T> dari Int32. Jika atribut tidak ada, maka jenis nullable diatur ke null. Sebelum menggunakan properti ini, Anda harus memastikan bahwa Attribute metode tidak mengembalikan null.

Lihat juga

• SetValue(Object)
• Name
• ToString()
• Gambaran umum LINQ ke XML