C# 空值條件運算符（對於開發者的運行原理）

if (employee != null)
{
    var name = employee.FirstName;
}

If employee IsNot Nothing Then
	Dim name = employee.FirstName
End If

var name = employee?.FirstName;

Dim name = employee?.FirstName

var name = employee?.FirstName ?? "Unknown";

Dim name = If(employee?.FirstName, "Unknown")

var firstName = employees?[0]?.FirstName ?? "Unknown";

Dim firstName = If(employees?(0)?.FirstName, "Unknown")

if (PropertyChanged != null)
{
    PropertyChanged(this, new PropertyChangedEventArgs(name));
}

If PropertyChanged IsNot Nothing Then
	PropertyChanged(Me, New PropertyChangedEventArgs(name))
End If

PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));

If PropertyChanged IsNot Nothing Then
	PropertyChanged.Invoke(Me, New PropertyChangedEventArgs(name))
End If

using System.ComponentModel;

// Define a Person class that implements the INotifyPropertyChanged interface
public class Person : INotifyPropertyChanged
{
    private string name;

    // Event that is raised when a property changes
    public event PropertyChangedEventHandler PropertyChanged;

    // Property for the person's name with a getter and setter
    public string Name
    {
        get { return name; }
        set
        {
            if (name != value)
            {
                name = value;
                OnPropertyChanged(nameof(Name)); // Notify that the property has changed
            }
        }
    }

    // Method to invoke the PropertyChanged event safely using the null conditional operator
    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

class Program
{
    static void Main(string[] args)
    {
        // Create a new Person instance and subscribe to the PropertyChanged event
        Person person = new Person();
        person.PropertyChanged += (sender, e) =>
        {
            Console.WriteLine($"{e.PropertyName} property has changed.");
        };

        // Change the person's name, triggering the PropertyChanged event
        person.Name = "Iron Software";
    }
}

Imports System.ComponentModel

' Define a Person class that implements the INotifyPropertyChanged interface
Public Class Person
	Implements INotifyPropertyChanged

'INSTANT VB NOTE: The field name was renamed since Visual Basic does not allow fields to have the same name as other class members:
	Private name_Conflict As String

	' Event that is raised when a property changes
	Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged

	' Property for the person's name with a getter and setter
	Public Property Name() As String
		Get
			Return name_Conflict
		End Get
		Set(ByVal value As String)
			If name_Conflict <> value Then
				name_Conflict = value
				OnPropertyChanged(NameOf(Name)) ' Notify that the property has changed
			End If
		End Set
	End Property

	' Method to invoke the PropertyChanged event safely using the null conditional operator
	Protected Overridable Sub OnPropertyChanged(ByVal propertyName As String)
		RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(propertyName))
	End Sub
End Class

Friend Class Program
	Shared Sub Main(ByVal args() As String)
		' Create a new Person instance and subscribe to the PropertyChanged event
		Dim person As New Person()
		AddHandler person.PropertyChanged, Sub(sender, e)
			Console.WriteLine($"{e.PropertyName} property has changed.")
		End Sub

		' Change the person's name, triggering the PropertyChanged event
		person.Name = "Iron Software"
	End Sub
End Class

using IronPdf;

class Program
{
    static void Main(string[] args)
    {
        var renderer = new ChromePdfRenderer();

        // 1. Convert HTML String to PDF
        var htmlContent = "<h1>Hello, IronPDF!</h1><p>This is a PDF from an HTML string.</p>";
        var pdfFromHtmlString = renderer.RenderHtmlAsPdf(htmlContent);
        pdfFromHtmlString.SaveAs("HTMLStringToPDF.pdf");

        // 2. Convert HTML File to PDF
        var htmlFilePath = "path_to_your_html_file.html"; // Specify the path to your HTML file
        var pdfFromHtmlFile = renderer.RenderHtmlFileAsPdf(htmlFilePath);
        pdfFromHtmlFile.SaveAs("HTMLFileToPDF.pdf");

        // 3. Convert URL to PDF
        var url = "http://ironpdf.com"; // Specify the URL
        var pdfFromUrl = renderer.RenderUrlAsPdf(url);
        pdfFromUrl.SaveAs("URLToPDF.pdf");
    }
}

Imports IronPdf

Friend Class Program
	Shared Sub Main(ByVal args() As String)
		Dim renderer = New ChromePdfRenderer()

		' 1. Convert HTML String to PDF
		Dim htmlContent = "<h1>Hello, IronPDF!</h1><p>This is a PDF from an HTML string.</p>"
		Dim pdfFromHtmlString = renderer.RenderHtmlAsPdf(htmlContent)
		pdfFromHtmlString.SaveAs("HTMLStringToPDF.pdf")

		' 2. Convert HTML File to PDF
		Dim htmlFilePath = "path_to_your_html_file.html" ' Specify the path to your HTML file
		Dim pdfFromHtmlFile = renderer.RenderHtmlFileAsPdf(htmlFilePath)
		pdfFromHtmlFile.SaveAs("HTMLFileToPDF.pdf")

		' 3. Convert URL to PDF
		Dim url = "http://ironpdf.com" ' Specify the URL
		Dim pdfFromUrl = renderer.RenderUrlAsPdf(url)
		pdfFromUrl.SaveAs("URLToPDF.pdf")
	End Sub
End Class