Walkthrough: Writing a Visualizer in C#

Article
09/01/2022
9 minutes to read

Applies to: Visual Studio Visual Studio for Mac Visual Studio Code

This walkthrough shows how to write a simple visualizer by using C#. The visualizer you will create in this walkthrough displays the contents of a string using a Windows Form. This simple string visualizer is not especially useful in itself, but it shows the basic steps that you must follow to create more useful visualizers for other data types.

Note

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Visualizer code must be placed in a DLL, which will be read by the debugger. Therefore, the first step is to create a Class Library project for the DLL.

Create a visualizer manually

Follow the tasks below to create a visualizer.

To create a class library project

Create a new class library project.

Choose File > New > Project. In the language drop-down, choose C#. In the search box, type class library, and then choose Class Library (.NET Framework). Click Next. In the dialog box that appears, type the name MyFirstVisualizer, and then click Create.

For the visualizer project, make sure you select a .NET Framework class library and not .NET. Although the visualizer needs to be .NET Framework, the calling app can be .NET.

After 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. Before you add the reference, however, you must rename some classes so that they have meaningful names.

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

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

Note

Visual Studio automatically changes the class declaration in DebuggerSide.cs to match the new file name.
In Solution Explorer, right-click References and choose Add Reference on the shortcut menu.
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.cs, add the following to the using directives:
```
using Microsoft.VisualStudio.DebuggerVisualizers;
```
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 inherits from the base class DialogDebuggerVisualizer.

To inherit from DialogDebuggerVisualizer

In DebuggerSide.cs, go to the following line of code:
```
public class DebuggerSide
```
Change the code to:
```
public class DebuggerSide : 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 override void Show(IDialogVisualizerService windowService, IVisualizerObjectProvider objectProvider)
{
}
```
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 using directive for System.Windows.Forms.

To add System.Windows.Forms

In Solution Explorer, right-click References and choose Add Reference on the shortcut menu.
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 to the using directives:
```
using System.Windows.Forms;
```
Now, you will add some code to create and show the user interface for your visualizer. Because this is your first visualizer, we 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, choose Build MyFirstVisualizer. The project should build successfully. Correct any build errors before continuing.

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.cs, after the using directives but before namespace MyFirstVisualizer:

[assembly:System.Diagnostics.DebuggerVisualizer(
typeof(MyFirstVisualizer.DebuggerSide),
typeof(VisualizerObjectSource),
Target = typeof(System.String),
Description = "My First Visualizer")]

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

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:

public static void TestShowVisualizer(object objectToVisualize)
{
   VisualizerDevelopmentHost visualizerHost = new VisualizerDevelopmentHost(objectToVisualize, typeof(DebuggerSide));
   visualizerHost.ShowVisualizer();
}

On the Build menu, choose 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.

Choose File > New > Project. In the language drop-down, choose C#. In the search box, type console app, and then choose either Console App (.NET Framework) or Console Application for .NET. Click Next. In the dialog box that appears, type the name MyTestConsole, and then click Create.

Note

If you want to easily test the visualizer using a test harness, create a .NET Framework console app. You can create a .NET console app instead, but the test harness described later is not yet supported for .NET, so you will need to install the visualizer to test it. For a .NET console app, first create the console app here, add the required DLL and project references, and then follow steps described in Add a debuggee-side data object. For ASP.NET Core scenarios, see Special debugger side considerations for .NET 5.0+.

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

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

To add code to MyTestConsole

In Solution Explorer, right-click Program.cs and choose Rename on the shortcut menu.
Edit the name from Program.cs to something more meaningful, such as TestConsole.cs.

Note

Visual Studio automatically changes the class declaration in TestConsole.cs to match the new file name.
In TestConsole.cs, add the following code to the using directives:
```
using MyFirstVisualizer;
```
In method Main, add the following code:
```
String myString = "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 choose Set as Startup Project on the shortcut menu.
On the Debug menu, choose Start.

The console application starts and 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.

Add a debuggee-side data object

In this section, you switch from the System.String data object to a custom data object.

In Solution Explorer, right-click the solution, choose Add, and then click New Project. In the language drop-down, choose C#. In the search box, type class library, and then choose either Class Library (.NET Framework) or Class Library for .NET Standard.

Note

If you are using a .NET Framework test console app, make sure you create a .NET Framework class library project.
Click Next. In the dialog box that appears, type the name MyDataObject, and then click Create.
(.NET Standard class library only) In Solution Explorer, right-click the project and choose Edit Project File. Change the <TargetFramework> value to netstandard2.0.
```
<TargetFramework>netstandard2.0</TargetFramework>
```
Inside the MyDataObject namespace, replace the default code with the following code.
```
[Serializable] 
public class CustomDataObject
{
   public CustomDataObject()
   {
      this.MyData = "MyTestData";
   }
   public string MyData { get; set; }
}
```
For a read-only visualizer, such as in this example, it is not necessary to implement methods of VisualizerObjectSource.

Next, update the MyFirstVisualizer project to use the new data object.
In Solution Explorer under the MyFirstVisualizer project, right-click the References node and choose Add Reference.
Under Projects, select the MyDataObject project.
In the attribute code of DebuggerSide.cs, update the Target value, changing System.String to MyDataObject.CustomDataObject.
```
Target = typeof(MyDataObject.CustomDataObject),
```

In the MyFirstVisualizer project, replace the code for the Show method with the following code.

var data = objectProvider.GetObject() as MyDataObject.CustomDataObject;

// You can replace displayForm with your own custom Form or Control.  
Form displayForm = new Form();
displayForm.Text = data.MyData;
windowService.ShowDialog(displayForm);

The preceding code uses a property of the data object to show in the Form's title.

Next, update the console app to use the custom data object.

In Solution Explorer under the MyTestConsole project, right-click the References or Dependencies node, and add a project reference to MyDataObject.

In Program.cs, replace the code in the Main method with the following code.

// String myString = "Hello, World";
CustomDataObject customDataObject = new CustomDataObject();

DebuggerSide.TestShowVisualizer(customDataObject);

(.NET console app) Enclose the call to TestShowVisualizer in a try-catch statement, since the test harness is unsupported.
```
try
{
      DebuggerSide.TestShowVisualizer(customDataObject);
}
catch (Exception) {
}
```
The console app needs a runtime reference to the visualizer. You can maintain the reference by keeping the preceding code instead of commenting it out.
For a .NET Framework console app, you can run the test harness (press F5), or you can follow instructions in How to: Install a Visualizer.

If you run the app using the test harness, the app shows the Windows Form.
For a .NET console app, copy the MyFirstVisualizer.dll and the MyDataObject.dll to the folders described in How to: Install a Visualizer.
After installing the visualizer, set a breakpoint, run the console app, and hover over customDataObject. If everything is set up correctly, you should see the magnifying glass icon .

When you choose MyFirstVisualizer from the magnifying glass, you will see the Form with the data object text in the title.