#WinML – How to create a #Windows10 App using #YOLO for object detection (2 of 4)

Windows 10 and YOLOV2 for Object Detection Series


Now we already have downloaded the YoloV2 ONNX file. We can create an UWP App to use the model. Here’s the step by step and some comments

1. We create a new Windows 10 UWP App. As always the name is super original


2. We are going to use the camera as images source to be processed with YoloV2. There are many examples of how to do this. In this case we will use a control of Windows Community Toolkit V 3.0 (as I wrote in a previous post). We add the following Packages Via NuGet

  • Microsoft.Toolkit.Uwp.UI
  • Microsoft.Toolkit.Uwp.UI.Controls


3. We add a control CameraPreview In our Xaml and we’re already 2 lines away of having the camera working.


4. We enable the necessary permissions to use the camera in the app manifest. With The following lines our app have a functional camera


5. The time has come to start using YoloV2. The latest versions of Visual Studio 2017 allow us to import an ONNX model into a project and the IDE will create the classes needed to work with it. We add as an existing file to the file [Tiny-YOLOv2. Onnx].

Our solution should be similar to the following


6. The class that is generated in VS to work with the model It’s pretty ugly.


7. My suggestion, replace [8d4d0fa662b14686b1865e0e6d3c598eByTinyYoloV2]


8. Now we can see the generated class and within it we can find 3 classes

  • An Input class for the Model
  • An Output class for the Model
  • A class to work with the Model

It’s time to load the model into our App. We do this before initializing the camera as shown in the following Code


9. Because we will use the model as part of our App, we have to define that it be treated as a Content in the process of Build


10. The next step is to evaluate a Frame Of the camera with the YOLOV2 model. Here the code shows us how we use the classes we create when we import the model.

11. Finally a Break Point is an useful way to show the output of the model and the information of the model output, which we will have to process later.



Well, at this point we are already using the model YoloV2 to analyze the frames of the camera. In the following posts I’ll write on how to work with the output of the model to get information which makes sense to us!

Important: At some point I should write about the model conversion capabilities that Visual Studio Tools brings to us For AI.

Happy Coding!

Greetings @ Toronto

El Bruno


57 thoughts on “#WinML – How to create a #Windows10 App using #YOLO for object detection (2 of 4)”

  1. Hi El Bruno,

    Excellent tutorial.

    Between steps #3 and #4, I cannot seem to initialize my Camera as I am receiving red error lines under CameraPreview in my MainPage.xaml.cs script:

    await CameraPreview.StartAsync();
    CameraPreview.CameraHelper.FrameArrived += CameraHelper_FrameArrived;

    Also, I see a difference in the MainPage.xaml code for the CameraPreview grid:

    Do you know what my issue may be?


    Liked by 1 person

    1. Fixed it in the MainPage.xaml.cs script:

      protected override async void OnNavigatedTo(NavigationEventArgs e)

      await CameraPreviewControl.StartAsync();
      CameraPreviewControl.CameraHelper.FrameArrived += CameraHelper_FrameArrived;

      Here is the code for the XAML:

      Liked by 1 person

        1. Hi elbruno,
          I have a problem with adding Tiny-YOLOv2.cs file into my project. Actually, when I add another YOLO file there is no problem and the .cs file will be added automatically. But, when I wanna try the one you recommended, The .cs file does not show up automatically. Can please let me know what the problem can be?


  2. I guess I’m missing something but even form your github I have a NullReferenceException with a null learning model on EvaluateAsync line in FrameArrived method, any clue ?

    Liked by 1 person

  3. Unable to load the Tiny-YOLOv2.onnx in Visual Studio 2017 i get the error:

    Tiny-YOLOv2.onnx -l CS -n VanUI -t VS_Marketplace’ failed with exit code 1
    mlgen failed: Node:batchnorm Required attribute ‘consumed_inputs’ is missing.


  4. Hi,
    I’m not a specialist in VS and I’m having a hard time to understand what do you mean by “We add as an existing file to the file [Tiny-YOLOv2. Onnx].” I add the onnx file to my project but the .cs file is not created automatically. I’m using Visual Studio Community 2017, Version 15.9.16.

    Thank you very much.. your post has been very useful to me,


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