c# code 39 checksum CH AP T ER 5 VA LI D AT IN G X ML D OC UMEN TS in Visual C#.NET

Generation ANSI/AIM Code 39 in Visual C#.NET CH AP T ER 5 VA LI D AT IN G X ML D OC UMEN TS

In the preceding example, our XML document doesn t use a namespace. If it did, we would have to make two changes to our schema and XML documents: Add the targetNamespace attribute to the schema declaration. Use the xsi:schemaLocation attribute instead of the xsi:noNamespaceSchemaLocation attribute. Listing 5-13 shows the modified schema, and Listing 5-14 shows the modified XML document. Listing 5-13. Schema with Target Namespace <xs:schema attributeFormDefault="qualified" elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="myns" xmlns="myns"> ... As you can see, the schema now has a targetNamespace attribute that specifies the target namespace as myns. The XML document must use this namespace, as illustrated in Listing 5-14. Listing 5-14. XML Document with Namespace <myns:employees xmlns:myns="myns" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="myns employeesns.xsd"> <myns:employee myns:employeeid="1"> <myns:firstname>Nancy</myns:firstname> ... Note the markup in bold. The root element now declares a namespace called myns, and instead of xsi:noNamespaceSchemaLocation it now uses an xsi:schemaLocation attribute. Observe carefully how the attribute value is specified: it must contain the namespace name, a space, and then the URL of the XSD file.

If you find yourself using the same schema files again and again, consider adding your schema to the schema cache. Once you store a schema in the schema cache, you can access it readily in the XML editor of Visual Studio. The schema cache can be seen from the XML Schemas menu option of Visual Studio. Note that the XML menu option is visible only when you open an XML file in the Visual Studio editor. Figure 5-14 shows the schemas available by default.

Figure 5-14. Schema set of Visual Studio You can add or remove schemas from the cache by clicking the Add or Remove buttons, respectively. Once you ve added a particular schema, you can use it while writing an XML document by selecting the Use this schema option of the schema set dialog (see Figure 5-15).

The XmlReader class provides you with a way to validate XML documents by using its Create() method, which accepts the URL of the XML document and an instance of the XmlReaderSettings class. The XmlReaderSettings class configures the XmlReader class and can be used to indicate your intention of validating XML documents. You can also wire up an event handler to receive notification about validation errors. The XmlReader instance returned by the Create() method can be used to read the XML document in the same way as you learned in 3. To illustrate how to use XmlReader to validate XML documents, you will develop an application like the one shown in Figure 5-16.

Figure 5-16. Application for validating an XML document by using the XmlReader class The application consists of two text boxes for accepting the XML document filename and the DTD or schema filename, respectively. The radio buttons indicate whether you are validating against a DTD or schema. Clicking the Validate button validates the document. Any errors encountered during the validation process are indicated via a message box. Listing 5-15 shows the complete code of the application. Listing 5-15. Validating an XML Document by Using XmlReader private void button1_Click(object sender, EventArgs e) { XmlReaderSettings settings = new XmlReaderSettings(); if(radioButton1.Checked) { settings.ProhibitDtd = false; settings.ValidationType = ValidationType.DTD; } else { settings.Schemas.Add("", textBox2.Text); settings.ValidationType=ValidationType.Schema; } settings.ValidationEventHandler += new ValidationEventHandler(OnValidationError); XmlReader reader = XmlReader.Create(textBox1.Text, settings); while (reader.Read()) { //you can put code here //that reads and processes //the document }

reader.Close(); MessageBox.Show("Validation over"); } If the XML document is to be validated against a DTD (as indicated by the radio buttons), the ProhibitDtd property of the XmlReaderSettings class is set to false. The ProhibitDtd property decides whether validation against a DTD is allowed. By default this property is true. If the document is to be validated against an XSD schema, the schema is added to the Schemas collection, which can accept an in-memory schema in the form of an XmlSchema class or a file path. The Add() method of the schemas collection used by our code accepts the target namespace and schema file path. The ValidationType property indicates whether the XmlReader should perform validation and whether to use a DTD or a schema. The ValidationType property is an enumeration of type ValidationType and has five possible values, as listed in Table 5-3.