C# Virtual 关键字（对开发者的作用）

public class Shape
{
    public virtual double Area()
    {
        return 0; // Default implementation, returns 0
    }
}

Public Class Shape
	Public Overridable Function Area() As Double
		Return 0 ' Default implementation, returns 0
	End Function
End Class

public class Circle : Shape
{
    public double Radius { get; set; }
    public Circle(double radius)
    {
        Radius = radius;
    }
    public override double Area()
    {
        return Math.PI * Radius * Radius; // Own implementation for circle area
    }
}

Public Class Circle
	Inherits Shape

	Public Property Radius() As Double
	Public Sub New(ByVal radius As Double)
		Me.Radius = radius
	End Sub
	Public Overrides Function Area() As Double
		Return Math.PI * Radius * Radius ' Own implementation for circle area
	End Function
End Class

public class Program
{
    public static void Main(string [] args)
    {
        Shape myShape = new Shape();
        Shape myCircle = new Circle(5);
        Console.WriteLine($"Shape area: {myShape.Area()}");
        Console.WriteLine($"Circle area: {myCircle.Area()}");
    }
}

Public Class Program
	Public Shared Sub Main(ByVal args() As String)
		Dim myShape As New Shape()
		Dim myCircle As Shape = New Circle(5)
		Console.WriteLine($"Shape area: {myShape.Area()}")
		Console.WriteLine($"Circle area: {myCircle.Area()}")
	End Sub
End Class

public class BasicPdfRenderer
{
    // Virtual method allowing customization in derived classes
    public virtual byte [] RenderHtmlToPdf(string htmlContent)
    {
        // Use IronPDF to render PDF from HTML
        var renderer = new IronPdf.ChromePdfRenderer();
        var pdfDocument = renderer.RenderHtmlAsPdf(htmlContent);
        return pdfDocument.BinaryData;
    }
}
public class CustomPdfRenderer : BasicPdfRenderer
{
    // Overriding the base class method to implement custom rendering settings
    public override byte [] RenderHtmlToPdf(string htmlContent)
    {
        var renderer = new IronPdf.ChromePdfRenderer();
        var pdfDocument = renderer.RenderHtmlAsPdf(htmlContent);
        // Apply a prominent watermark to the PDF document
        pdfDocument.ApplyWatermark("<h2 style='color:red; font-size: 60px; opacity: 0.5; text-shadow: 2px 2px 5px grey;'>SAMPLE</h2>",
                                      30,
                                      IronPdf.Editing.VerticalAlignment.Middle,
                                      IronPdf.Editing.HorizontalAlignment.Center);
        // Return the binary data of the PDF document
        return pdfDocument.BinaryData;
    }
}
class Program
{
    static void Main(string [] args)
    {
        License.LicenseKey = "License-Key";
        // HTML content to be converted to PDF
        string htmlContent = "<h1>Hello, IronPDF!</h1><p>This is a simple PDF document generated from HTML.</p>";
        // Create an instance of CustomPdfRenderer
        CustomPdfRenderer renderer = new CustomPdfRenderer();
        // Call RenderHtmlToPdf method to generate PDF binary data
        byte [] pdfData = renderer.RenderHtmlToPdf(htmlContent);
        // Specify the file path to save the PDF
        string filePath = "f:\\CustomRenderedPdf.pdf";
        // Save the binary data to a file
        File.WriteAllBytes(filePath, pdfData);
        Console.WriteLine($"PDF generated and saved to {filePath}");
    }
}

Public Class BasicPdfRenderer
	' Virtual method allowing customization in derived classes
	Public Overridable Function RenderHtmlToPdf(ByVal htmlContent As String) As Byte()
		' Use IronPDF to render PDF from HTML
		Dim renderer = New IronPdf.ChromePdfRenderer()
		Dim pdfDocument = renderer.RenderHtmlAsPdf(htmlContent)
		Return pdfDocument.BinaryData
	End Function
End Class
Public Class CustomPdfRenderer
	Inherits BasicPdfRenderer

	' Overriding the base class method to implement custom rendering settings
	Public Overrides Function RenderHtmlToPdf(ByVal htmlContent As String) As Byte()
		Dim renderer = New IronPdf.ChromePdfRenderer()
		Dim pdfDocument = renderer.RenderHtmlAsPdf(htmlContent)
		' Apply a prominent watermark to the PDF document
		pdfDocument.ApplyWatermark("<h2 style='color:red; font-size: 60px; opacity: 0.5; text-shadow: 2px 2px 5px grey;'>SAMPLE</h2>", 30, IronPdf.Editing.VerticalAlignment.Middle, IronPdf.Editing.HorizontalAlignment.Center)
		' Return the binary data of the PDF document
		Return pdfDocument.BinaryData
	End Function
End Class
Friend Class Program
	Shared Sub Main(ByVal args() As String)
		License.LicenseKey = "License-Key"
		' HTML content to be converted to PDF
		Dim htmlContent As String = "<h1>Hello, IronPDF!</h1><p>This is a simple PDF document generated from HTML.</p>"
		' Create an instance of CustomPdfRenderer
		Dim renderer As New CustomPdfRenderer()
		' Call RenderHtmlToPdf method to generate PDF binary data
		Dim pdfData() As Byte = renderer.RenderHtmlToPdf(htmlContent)
		' Specify the file path to save the PDF
		Dim filePath As String = "f:\CustomRenderedPdf.pdf"
		' Save the binary data to a file
		File.WriteAllBytes(filePath, pdfData)
		Console.WriteLine($"PDF generated and saved to {filePath}")
	End Sub
End Class