Home > System > Xml > XmlReader > CanResolveEntity

XmlReader.CanResolveEntity Method

Namespace: System.Xml Assembly: System.Xml.dll

Description

Gets a value indicating whether the XmlReader can resolve entities.

public virtual bool CanResolveEntity { get; }

Return Value

bool

true if the XmlReader can resolve entities; otherwise, false.

Remarks

When this property is true, the XmlReader.ResolveEntity method can be called to resolve entities. This property is true for XmlReader implementations that support entity resolution (e.g., XmlTextReader) and false for those that do not.

If you attempt to call ResolveEntity when CanResolveEntity is false, an InvalidOperationException will be thrown.

Usage
Example
Inheritance
Exceptions

Usage

The CanResolveEntity property is typically used to check if the current XmlReader implementation supports entity resolution before attempting to call the ResolveEntity method. This helps in writing more robust XML parsing code.


using System.Xml;

// Assume xmlReader is an initialized XmlReader instance
XmlReader xmlReader = XmlReader.Create("your_xml_file.xml");

if (xmlReader.CanResolveEntity)
{
    Console.WriteLine("The XmlReader can resolve entities.");
    // You can now safely call xmlReader.ResolveEntity() if needed.
}
else
{
    Console.WriteLine("The XmlReader cannot resolve entities.");
}

xmlReader.Close();

Example

This example demonstrates how to use the CanResolveEntity property to determine if an XmlReader supports entity resolution.


using System;
using System.Xml;
using System.IO;

public class XmlReaderEntityResolution
{
    public static void Main(string[] args)
    {
        string xmlString = @"
            <?xml version=""1.0"" encoding=""UTF-8""?>
            <root>
                <message>Hello, &world;</message>
            </root>";

        // Using XmlTextReader which supports entity resolution
        using (StringReader stringReader = new StringReader(xmlString))
        using (XmlReader reader = new XmlTextReader(stringReader))
        {
            Console.WriteLine("--- Using XmlTextReader ---");
            Console.WriteLine($"CanResolveEntity: {reader.CanResolveEntity}");

            // ResolveEntity is typically used in conjunction with DtdProcessing.Parse
            // to process external entities. For this simple example, we'll just check.
            if (reader.CanResolveEntity)
            {
                // In a real scenario, you would call ResolveEntity() when needed
                // to process a specific entity.
            }
            Console.WriteLine();
        }

        // Using a reader that might not support entity resolution (e.g., a simple stream reader)
        // Note: XmlReader.Create by default might disable DTD processing depending on settings.
        // To demonstrate a non-resolving reader, let's simulate a scenario where it's disabled.
        XmlReaderSettings settings = new XmlReaderSettings
        {
            DtdProcessing = DtdProcessing.Ignore // Explicitly ignore DTDs
        };

        using (StringReader stringReader = new StringReader(xmlString))
        using (XmlReader reader = XmlReader.Create(stringReader, settings))
        {
            Console.WriteLine("--- Using XmlReader.Create with DtdProcessing.Ignore ---");
            Console.WriteLine($"CanResolveEntity: {reader.CanResolveEntity}"); // This will likely be false
            Console.WriteLine();
        }
    }
}

Inheritance

System.Object > System.Xml.XmlReader

This property is part of the abstract base class XmlReader and its concrete implementations.

Exceptions

Calling ResolveEntity when CanResolveEntity is false will throw: