XML 架构可以包含<xs:import />和<xs:include /><xs:redefine />元素。 这些架构元素指的是其他 XML 架构，这些架构可以用于补充包含或导入它们的架构结构。
XmlSchemaImport、XmlSchemaInclude和XmlSchemaRedefine类映射到在架构对象模型（SOM）API中的这些元素。
包括或导入 XML 架构
下面的代码示例使用地址架构补充 在生成 XML 架构 主题中创建的客户架构。 使用地址架构补充客户架构可使地址类型在客户架构中可用。
地址架构可以通过使用<xs:include />或<xs:import />元素来运用地址架构 as-is的组件，或者使用<xs:redefine />元素修改任何组件以适应客户架构的需求。 由于地址架构与 targetNamespace 客户架构不同，因此使用了 <xs:import /> 元素和导入语义。
代码示例在以下步骤中包括地址架构。
将客户架构和地址架构添加到新 XmlSchemaSet 对象，然后对其进行编译。 由ValidationEventHandler 委托处理在读取或编译架构时遇到的任何架构验证警告和错误。
从XmlSchema中循环访问XmlSchemaSet属性以检索客户架构和地址架构的已Schemas编译对象。 由于架构已编译，可以访问Compilation-Infoset （PSCI）架构后属性。
创建一个XmlSchemaImport对象，将导入的Namespace属性设置为地址架构的命名空间，将导入的Schema属性设置为地址架构中的XmlSchema对象，并将导入添加到客户架构的Includes属性。
使用XmlSchema类的方法Reprocess和Compile重新处理并编译客户架构中的XmlSchemaSet对象的修改，并将其写入控制台。
最后，以递归方式使用 Includes 客户架构的属性将导入到客户架构中的所有架构写入控制台。 该 Includes 属性提供对添加到架构的所有包含项、导入项或重新定义项的访问权。
下面是完整的代码示例以及写入控制台的客户和地址架构。
using System;
using System.Xml;
using System.Xml.Schema;
class XmlSchemaImportExample
{
static void Main(string[] args)
{
// Add the customer and address schemas to a new XmlSchemaSet and compile them.
// Any schema validation warnings and errors encountered reading or
// compiling the schemas are handled by the ValidationEventHandler delegate.
XmlSchemaSet schemaSet = new XmlSchemaSet();
schemaSet.ValidationEventHandler += new ValidationEventHandler(ValidationCallback);
schemaSet.Add("http://www.tempuri.org", "customer.xsd");
schemaSet.Add("http://www.example.com/IPO", "address.xsd");
schemaSet.Compile();
// Retrieve the compiled XmlSchema objects for the customer and
// address schema from the XmlSchemaSet by iterating over
// the Schemas property.
XmlSchema customerSchema = null;
XmlSchema addressSchema = null;
foreach (XmlSchema schema in schemaSet.Schemas())
{
if (schema.TargetNamespace == "http://www.tempuri.org")
customerSchema = schema;
else if (schema.TargetNamespace == "http://www.example.com/IPO")
addressSchema = schema;
}
// Create an XmlSchemaImport object, set the Namespace property
// to the namespace of the address schema, the Schema property
// to the address schema, and add it to the Includes property
// of the customer schema.
XmlSchemaImport import = new XmlSchemaImport();
import.Namespace = "http://www.example.com/IPO";
import.Schema = addressSchema;
customerSchema.Includes.Add(import);
// Reprocess and compile the modified XmlSchema object
// of the customer schema and write it to the console.
schemaSet.Reprocess(customerSchema);
schemaSet.Compile();
customerSchema.Write(Console.Out);
// Recursively write all of the schemas imported into the
// customer schema to the console using the Includes
// property of the customer schema.
RecurseExternals(customerSchema);
}
static void RecurseExternals(XmlSchema schema)
{
foreach (XmlSchemaExternal external in schema.Includes)
{
if (external.SchemaLocation != null)
{
Console.WriteLine($"External SchemaLocation: {external.SchemaLocation}");
}
if (external is XmlSchemaImport)
{
XmlSchemaImport import = external as XmlSchemaImport;
Console.WriteLine($"Imported namespace: {import.Namespace}");
}
if (external.Schema != null)
{
external.Schema.Write(Console.Out);
RecurseExternals(external.Schema);
}
}
}
static void ValidationCallback(object sender, ValidationEventArgs args)
{
if (args.Severity == XmlSeverityType.Warning)
Console.Write("WARNING: ");
else if (args.Severity == XmlSeverityType.Error)
Console.Write("ERROR: ");
Console.WriteLine(args.Message);
}
}
Imports System.Xml
Imports System.Xml.Schema
Class XmlSchemaImportExample
Shared Sub Main()
' Add the customer and address schemas to a new XmlSchemaSet and compile them.
' Any schema validation warnings and errors encountered reading or
' compiling the schemas are handled by the ValidationEventHandler delegate.
Dim schemaSet As XmlSchemaSet = New XmlSchemaSet()
AddHandler schemaSet.ValidationEventHandler, AddressOf ValidationCallback
schemaSet.Add("http://www.tempuri.org", "customer.xsd")
schemaSet.Add("http://www.example.com/IPO", "address.xsd")
schemaSet.Compile()
' Retrieve the compiled XmlSchema objects for the customer and
' address schema from the XmlSchemaSet by iterating over
' the Schemas property.
Dim customerSchema As XmlSchema = Nothing
Dim addressSchema As XmlSchema = Nothing
For Each schema As XmlSchema In schemaSet.Schemas()
If schema.TargetNamespace = "http://www.tempuri.org" Then
customerSchema = schema
ElseIf schema.TargetNamespace = "http://www.example.com/IPO" Then
addressSchema = schema
End If
Next
' Create an XmlSchemaImport object, set the Namespace property
' to the namespace of the address schema, the Schema property
' to the address schema, and add it to the Includes property
' of the customer schema.
Dim import As XmlSchemaImport = New XmlSchemaImport()
import.Namespace = "http://www.example.com/IPO"
import.Schema = addressSchema
customerSchema.Includes.Add(import)
' Reprocess and compile the modified XmlSchema object
' of the customer schema and write it to the console.
schemaSet.Reprocess(customerSchema)
schemaSet.Compile()
customerSchema.Write(Console.Out)
' Recursively write all of the schemas imported into the
' customer schema to the console using the Includes
' property of the customer schema.
RecurseExternals(customerSchema)
End Sub
Shared Sub RecurseExternals(ByVal schema As XmlSchema)
For Each external As XmlSchemaExternal In Schema.Includes
If Not external.SchemaLocation = Nothing Then
Console.WriteLine("External SchemaLocation: {0}", external.SchemaLocation)
End If
If external.GetType() Is GetType(XmlSchemaImport) Then
Dim import As XmlSchemaImport = CType(external, XmlSchemaImport)
Console.WriteLine("Imported namespace: {0}", import.Namespace)
End If
If Not external.Schema Is Nothing Then
external.Schema.Write(Console.Out)
RecurseExternals(external.Schema)
End If
Next
End Sub
Shared Sub ValidationCallback(ByVal sender As Object, ByVal args As ValidationEventArgs)
If args.Severity = XmlSeverityType.Warning Then
Console.Write("WARNING: ")
Else
If args.Severity = XmlSeverityType.Error Then
Console.Write("ERROR: ")
End If
End If
Console.WriteLine(args.Message)
End Sub
End Class
<?xml version="1.0" encoding="utf-8"?>
<xs:schema xmlns:tns="http://www.tempuri.org" targetNamespace="http://www.tempuri.org" xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:import namespace="http://www.example.com/IPO" />
<xs:element name="Customer">
<xs:complexType>
<xs:sequence>
<xs:element name="FirstName" type="xs:string" />
<xs:element name="LastName" type="tns:LastNameType" />
</xs:sequence>
<xs:attribute name="CustomerId" type="xs:positiveInteger" use="required" />
</xs:complexType>
</xs:element>
<xs:simpleType name="LastNameType">
<xs:restriction base="xs:string">
<xs:maxLength value="20" />
</xs:restriction>
</xs:simpleType>
</xs:schema>
<schema targetNamespace="http://www.example.com/IPO" xmlns="http://www.w3.org/2001/XMLSchema" xmlns:ipo="http://www.example.com/IPO">
<annotation>
<documentation xml:lang="en">
Addresses for International Purchase order schema
Copyright 2000 Example.com. All rights reserved.
</documentation>
</annotation>
<complexType name="Address">
<sequence>
<element name="name" type="string"/>
<element name="street" type="string"/>
<element name="city" type="string"/>
</sequence>
</complexType>
<complexType name="USAddress">
<complexContent>
<extension base="ipo:Address">
<sequence>
<element name="state" type="ipo:USState"/>
<element name="zip" type="positiveInteger"/>
</sequence>
</extension>
</complexContent>
</complexType>
<!-- other Address derivations for more countries or regions -->
<simpleType name="USState">
<restriction base="string">
<enumeration value="AK"/>
<enumeration value="AL"/>
<enumeration value="AR"/>
<!-- and so on ... -->
</restriction>
</simpleType>
</schema>
有关<xs:import />、<xs:include />和<xs:redefine />元素及XmlSchemaImport、XmlSchemaInclude和XmlSchemaRedefine类的详细信息，请参阅W3C XML 架构和System.Xml.Schema命名空间类参考文档。
