Walkthrough: Writing a Visualizer in Visual Basic

Article
05/27/2020

Applies to: Visual Studio Visual Studio for Mac

Note

This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here

This walkthrough shows how to write a simple visualizer by using Visual Basic. The visualizer you will create in this walkthrough displays the contents of a string using a Windows Forms message box. This simple string visualizer is a basic example to show how you can create visualizers for other data types more applicable to your projects.

Note

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Visualizer code must be placed in a DLL that will be read by the debugger. The first step is to create a class library project for the DLL.

Create and Prepare a Class Library Project

To create a class library project

Create a new class library project.

From the top menu bar, choose File > New > Project. In the left pane of the New project dialog box, under Visual Basic, choose .NET Standard, and then in the middle pane choose Class Library (.NET Standard).
Type an appropriate name for the class library, such as MyFirstVisualizer, and then click Create or OK.

When you have created the class library, you must add a reference to Microsoft.VisualStudio.DebuggerVisualizers.DLL, so that you can use the classes defined there. First, however, you give your project a meaningful name.

To rename Class1.vb and add Microsoft.VisualStudio.DebuggerVisualizers

In Solution Explorer, right-click Class1.vb, and on the shortcut menu, click Rename.
Change the name from Class1.vb to something meaningful, such as DebuggerSide.vb.

Note

Visual Studio automatically changes the class declaration in DebuggerSide.vb to match the new file name.
In Solution Explorer, right-click My First Visualizer, and on the shortcut menu, click Add Reference.
In the Add Reference dialog box, on the Browse tab, select Browse and find the Microsoft.VisualStudio.DebuggerVisualizers.DLL.

You can find the DLL in <Visual Studio Install Directory>\Common7\IDE\PublicAssemblies subdirectory of Visual Studio's installation directory.
Click OK.
In DebuggerSide.vb, add the following statement to the Imports statements:
```
Imports Microsoft.VisualStudio.DebuggerVisualizers
```

Add the Debugger-side Code

Now, you are ready to create the debugger-side code. This is the code that runs within the debugger to display the information that you want to visualize. First, you have to change the declaration of the DebuggerSide object so that it inherits from the base class DialogDebuggerVisualizer.

To inherit from DialogDebuggerVisualizer

In DebuggerSide.vb, go to the following line of code:
```
Public Class DebuggerSide
```
Edit the code so that it looks like this:
```
Public Class DebuggerSide
Inherits DialogDebuggerVisualizer
```
DialogDebuggerVisualizer has one abstract method, Show, that you must override.

To override the DialogDebuggerVisualizer.Show method

In public class DebuggerSide, add the following method:
```
Protected Overrides Sub Show(ByVal windowService As Microsoft.VisualStudio.DebuggerVisualizers.IDialogVisualizerService, ByVal objectProvider As Microsoft.VisualStudio.DebuggerVisualizers.IVisualizerObjectProvider)

    End Sub
```
The Show method contains the code that actually creates the visualizer dialog box, or other user interface, and displays the information that has been passed to the visualizer from the debugger. You must add the code that creates the dialog box and displays the information. In this walkthrough, you will do this using a Windows Forms message box. First, you must add a reference and Imports statement for System.Windows.Forms.

To add System.Windows.Forms

In Solution Explorer, right-click References, and on the shortcut menu, click Add Reference.
In the Add Reference dialog box, on the Browse tab, select Browse, and find the System.Windows.Forms.DLL.

You can find the DLL in C:\Windows\Microsoft.NET\Framework\v4.0.30319.
Click OK.
In DebuggerSide.cs, add the following statement to the Imports statements:
```
Imports System.Windows.Forms
```

Create Your Visualizer's User Interface

Now you will add some code to create and show the user interface for your visualizer. Because this is your first visualizer, you will keep the user interface simple and use a Message Box.

To show the visualizer output in a dialog box

In the Show method, add the following line of code:
```
MessageBox.Show(objectProvider.GetObject().ToString())
```
This example code does not include error handling. You should include error handling in a real visualizer, or any other kind of application.
On the Build menu, click Build MyFirstVisualizer. The project should build successfully. Correct any build errors before continuing.

Add the Necessary Attribute

That is the end of the debugger-side code. There is one more step, however: the attribute that tells the debuggee side which collection of classes comprises the visualizer.

To add the type to visualize for the debuggee-side code

In the debugger-side code, you specify the type to visualize (the object source) for the debuggee using the DebuggerVisualizerAttribute attribute. The Target property sets the type to visualize.

Add the following attribute code to DebuggerSide.vb, after the Imports statements but before namespace MyFirstVisualizer:

<Assembly: System.Diagnostics.DebuggerVisualizer(GetType(MyFirstVisualizer.DebuggerSide), GetType(VisualizerObjectSource), Target:=GetType(System.String), Description:="My First Visualizer")>

On the Build menu, click Build MyFirstVisualizer. The project should build successfully. Correct any build errors before continuing.

Create a Test Harness

At this point, your first visualizer is finished. If you have followed the steps correctly, you can build the visualizer and install it into Visual Studio. Before you install a visualizer into Visual Studio, however, you should test it to make sure that it runs correctly. You will now create a test harness to run the visualizer without installing it into Visual Studio.

To add a test method to show the visualizer

Add the following method to class public DebuggerSide:

Shared Public Sub TestShowVisualizer(ByVal objectToVisualize As Object)
    Dim visualizerHost As New VisualizerDevelopmentHost(objectToVisualize, GetType(DebuggerSide))
visualizerHost.ShowVisualizer()
End Sub

On the Build menu, click Build MyFirstVisualizer. The project should build successfully. Correct any build errors before continuing.

Next, you must create an executable project to call your visualizer DLL. For simplicity, use a console application project.

To add a console application project to the solution

In Solution Explorer, right-click the solution, choose Add, and then click New Project.

From the top menu bar, choose File > New > Project. In the left pane of the New project dialog box, under Visual Basic, choose Windows Desktop, and then in the middle pane choose Console App (.NET Framework).
Type an appropriate name for the class library, such as MyTestConsole, and then click Create or OK.

Now, you must add the necessary references so MyTestConsole can call MyFirstVisualizer.

To add necessary references to MyTestConsole

In Solution Explorer, right-click MyTestConsole, and on the shortcut menu, click Add Reference.
In the Add Reference dialog box, on the Browse tab, click Microsoft.VisualStudio.DebuggerVisualizers.
Click OK.
Right-click MyTestConsole, and then click Add Reference again.
In the Add Reference dialog box, click the Projects tab, and then select MyFirstVisualizer.
Click OK.

Finish Your Test Harness and Test Your Visualizer

Now, you will add the code to finish the test harness.

To add code to MyTestConsole

In Solution Explorer, right-click Program.vb, and on the shortcut menu, click Rename.
Edit the name from Module1.vb to something appropriate, such as TestConsole.vb.

Notice that Visual Studio automatically changes the class declaration in TestConsole.vb to match the new file name.
In TestConsole. vb, add the following Imports statement:
```
Imports MyFirstVisualizer
```
In method Main, add the following code:
```
Dim myString As String = "Hello, World"
DebuggerSide.TestShowVisualizer(myString)
```
Now you are ready to test your first visualizer.

To test the visualizer

In Solution Explorer, right-click MyTestConsole, and on the shortcut menu, click Set as Startup Project.
On the Debug menu, click Start.

The console application starts. The visualizer appears and displays the string "Hello, World."

Congratulations. You have just built and tested your first visualizer.

If you want to use your visualizer in Visual Studio rather than just calling it from the test harness, you have to install it. For more information, see How to: Install a Visualizer.

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