Note The VisitIdenti er method processes the token passed to it as a parameter in in VS .NET

Creator PDF-417 2d barcode in VS .NET Note The VisitIdenti er method processes the token passed to it as a parameter in

9. In the Class View window, right-click the ITokenVisitor interface, and then click Go To De nition. This action displays the ITokenVisitor.cs source le in the Code and Text Editor window. The ITokenVisitor interface contains one method for each type of token. The result of this hierarchy of interfaces, abstract classes, and classes is that you can create a class that implements the ITokenVisitor interface, create an instance of this class, and pass this instance as the parameter to the Accept method of a SourceFile object. For example:

class MyVisitor : ITokenVisitor { public void VisitIdentifier(string token) { ... } public void VisitKeyword(string token) { ... } } ... class Program { static void Main() { SourceFile source = new SourceFile(); MyVisitor visitor = new MyVisitor(); source.Accept(visitor); } }

The code in the Main method will result in each token in the source le calling the matching method in the visitor object. In the following exercise, you will create a class that derives from the ITokenVisitor interface and whose implementation displays the tokens from our hard-coded source le in a rich text box in color syntax (for example, keywords in blue) by using the visitor mechanism.

1. In Solution Explorer (click the Solution Explorer tab below the Class View window), double-click Window1.xaml to display the Color Syntax form in the Design View window.

13

You will use this form to test the framework. This form contains a button for opening a le to be tokenized and a rich text box for displaying the tokens:

The rich text box in the middle of the form is named codeText, and the button is named Open. Note A rich text box is like an ordinary text box except that it can display formatted content rather than simple, unformatted text. 2. Right-click the form, and then click View Code to display the code for the form in the Code and Text Editor window. 3. Locate the openClick method. This method is called when the user clicks the Open button. You must implement this method so that it displays the tokens de ned in the SourceFile class in the rich text box, by using a ColorSyntaxVisitor object. Add the code shown here in bold to the openClick method:

private void openClick(object sender, RoutedEventArgs e) { SourceFile source = new SourceFile(); ColorSyntaxVisitor visitor = new ColorSyntaxVisitor(codeText); source.Accept(visitor); }

Remember that the Accept method of the SourceFile class iterates through all the tokens, processing each one by using the speci ed visitor. In this case, the visitor is the ColorSyntaxVisitor object, which will render each token in color. Note In the current implementation, the Open button uses just data that is hard-coded in

the SourceFile class. In a fully functional implementation, the Open button would prompt the user for the name of a text le and then parse and tokenize it into the format shown in the SourceFile class before calling the Accept method.

4. Open the ColorSyntaxVisitor.cs le in the Code and Text Editor window. The ColorSyntaxVisitor class has been partially written. This class implements the ITokenVisitor interface and already contains two elds and a constructor to initialize a reference to the rich text box, named target, used to display tokens. Your task is to implement the methods inherited from the ITokenVisitor interface and also create a method that will write the tokens to the rich text box. 5. In the Code and Text Editor window, add the Write method to the ColorSyntaxVisitor class exactly as follows:

private void Write(string token, SolidColorBrush color) { target.AppendText(token); int offsetToStartOfToken = -1 * token.Length - 2; int offsetToEndOfToken = -2; TextPointer start = target.Document.ContentEnd.GetPositionAtOffset(offsetToStartOfToken); TextPointer end = target.Document.ContentEnd.GetPositionAtOffset(offsetToEndOfToken); TextRange text = new TextRange(start, end); text.ApplyPropertyValue(TextElement.ForegroundProperty, color); }

This code appends each token to the rich text box identi ed by the target variable using the speci ed color. The two TextPointer variables, start and end, indicate where the new token starts and ends in the rich text box control. (Don t worry about how these positions are calculated. If you re wondering, they are negative values because they are offset from the ContentEnd property.) The TextRange variable text obtains a reference to the portion of the text in the rich text box control displaying the newly appended token. The ApplyPropertyValue method sets the color of this text to the color speci ed as the second parameter. Each of the various visit methods in the ColorSyntaxVisitor class will call this Write method with an appropriate color to display color-coded results. 6. In the Code and Text Editor window, add the following methods that implement the ITokenVisitor interface to the ColorSyntaxVisitor class. Specify Brushes.Blue for keywords, Brushes.Green for StringLiterals, and Brushes.Black for all other methods. (Brushes is a class de ned in the System.Windows.Media namespace.) Notice that this code implements the interface explicitly; it quali es each method with the interface name.

void ITokenVisitor.VisitComment(string token) { Write(token, Brushes.Black); } void ITokenVisitor.VisitIdentifier(string token) { Write(token, Brushes.Black);