Getting Started with CVB.Net

Programming Questions .Net API
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8

Display a Stream (Windows Forms)

For this post, let’s create a new Windows Forms App (Visual C#) and call it CvbViewer:

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After the wizard finishes its work you should see an open Form1.cs [Design].

Don’t forget to disable the Prefer 32-bit check-box.

Before we can do anything useful we also need to add the Stemmer.Cvb.dll, Stemmer.Cvb.Forms.dll, Stemmer.Cvb.Aux.dll and Stemmer.Cvb.Extensions.dll to the references.

Open your Toolbox, right-click on the General tab and click on Choose items…

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After loading finishes first try to enter Stemmer in the Filter: text field. This should list:

  • Display
  • GenApiGrid
  • StreamHandler

If that doesn’t show you anything you can click on Browse… and enter

%CVB%Lib\Net

and choose Stemmer.Cvb.Forms. Then confirm this and the Choose Toolbox Items dialog with Ok. You now should see three new entries under General:

  • Display
  • GenApiGrid
  • StreamHandler
  1. We quickly add an “Open”-Button (openButton) and a “Grab”-CheckBox (grabCheckBox) and anchor them to the Bottom, Left.
  2. We add the StreamHandler as streamHandler to the Form1. It will be placed below the Designer window in the Components section.
  3. We add the Display as displayand anchor it Top, Bottom, Left, Right.

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As we finished our UI-design, we can double-click on the Open… button to create its Click handler and enter the following code:

private void openButton_Click(object sender, EventArgs e)
{
  try
  {
    Device device = FileDialogs.LoadByDialog(path => DeviceFactory.Open(path), "CVB Devices|*.vin;*.emu;*.avi");
    if (device == null)
      return; // canceled

    Device = device;
  }
  catch (IOException ex)
  {
    MessageBox.Show(ex.Message, "Error loading device", MessageBoxButtons.OK, MessageBoxIcon.Error);
  }
}

and

private Device Device
{
  get { return _device; }
  set
  {
    if (!ReferenceEquals(value, _device))
    {
      display.Image = value?.DeviceImage;
      streamHandler.Stream = value?.Stream;

      _device?.Dispose(); // old one is not needed anymore
      _device = value;
    }
  }
}
private Device _device;

To make this work add the following namespaces:

using Stemmer.Cvb;
using Stemmer.Cvb.Forms;
using System.IO;

We use the helper FileDialogs.LoadByDialog to easily open a FileDialog that returns the opened Device or null if canceled. This dialog supports avi- and emu-files as well a preconfigured vin-drivers.

We also utilize a Device Form1.Device property to manage life-time of prior loaded devices and to assign the DeviceImage to the display and the Device.Stream to the streamHandler. (If ?. looks unfamiliar: that is automatic null handling: null is assigned if value == null.)

When we run the app and load e.g. the GenICam.vin, we see a black image in the Display. This is normal as we don’t do “Auto Snap” and no data has been acquired, yet.

Finally let’s connect to the grabCheckBox’s CheckedChanged event by double-clicking on the CheckBox in the designer. Add the following code:

private void grabCheckBox_CheckedChanged(object sender, EventArgs e)
{
  if (grabCheckBox.Checked)
    streamHandler.Start();
  else
    streamHandler.Stop();

  openButton.Enabled = !grabCheckBox.Checked;
}

And that’s it. You have your life-display :cvb: app.

If you want to be correct and properly clean-up, move the void Dispose(bool disposing) (see the Dispose pattern for more info about this) method from the .Designer.cs into your implementation cs file and change it to:

protected override void Dispose(bool disposing)
{
  if (disposing)
  {
    components?.Dispose();
    Device?.Dispose();
  }
  base.Dispose(disposing);
}

components?.Dispose() will dispose the streamHandler, which will abort any ongoing acquisition. And last but not least we clean-up our opened Device. This is especially useful if you use your window as a dialog in your application and must ensure that the Device is not open anymore after the dialog is closed.

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