# Refresh available ports

**URL:** <https://forum.opentap.io/t/refresh-available-ports/540>\
**Category:** Ecosystem\
**Tags:** plugin\
**Created:** [December 2, 2021, 4:10pm UTC](https://forum.opentap.io/t/refresh-available-ports/540 "2021-12-02T16:10:04Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![lucappelman](https://avatars.discourse-cdn.com/v4/letter/l/e274bd/32.png) [@lucappelman](https://forum.opentap.io/u/lucappelman)\
**Post date:** [December 2, 2021, 4:10pm UTC](https://forum.opentap.io/t/refresh-available-ports/540/1 "2021-12-02T16:10:04Z")

</div>

We are working on a instrument using the System.IO.Ports library to connect to a COM port on windows.

Everything is working fine, but we can’t get OpenTAP to update the connected devices without restarting the whole program.

The behaviour I would like to see it that when someone clicks on the select box with the list of devices the list gets updated or, even better, catch a event when the connected devices change. So the user always sees a accurate list of available devices to choose from. I tried to use the `get` methods from the `public List<>` as wel as the public property which holds the current selected COM port. But with no success.

```csharp
private List<string> m_AvailablePorts;
public List<string> mAvailablePorts
{
    get {
        m_AvailablePorts = new List<string>( SerialPort.GetPortNames());
        return m_AvailablePorts;
    }
    private set
    { m_AvailablePorts = value; }
}

```

```csharp
[Display(Name: "COM Port", Group: "Connection", Order: 1.1)]
[AvailableValues( nameof( mAvailablePorts ))]
public string mComPort {
    get {
        m_AvailablePorts = new List<string>( SerialPort.GetPortNames());
        return mComPort;
    }
    set{ mComPort = value; } 
}

```

What would be the best solution to get a accurate list of currently connected COM port devices?

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<div class="post-metadata">

**Author:** ![david-wsd](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opentap.io/david-wsd/32/204_2.png) [@david-wsd](https://forum.opentap.io/u/david-wsd)\
**Post date:** [December 3, 2021, 12:15am UTC](https://forum.opentap.io/t/refresh-available-ports/540/2 "2021-12-03T00:15:49Z")

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I wouldn’t recommend updating available values from within the getter of mComPort.

I usually structure things as seen below, and I get updated available values every time I click the select button. If it’s not working for you, can you verify that SerialPort.GetPortNames() is returning what you expect?

```csharp
public List<string> mAvailablePorts
{
    get {
        return new List<string>( SerialPort.GetPortNames());
    }
}

[Display(Name: "COM Port", Group: "Connection", Order: 1.1)]
[AvailableValues( nameof( mAvailablePorts ))]
public string mComPort {get;set;}

```

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<div class="post-metadata">

**Author:** ![lucappelman](https://avatars.discourse-cdn.com/v4/letter/l/e274bd/32.png) [@lucappelman](https://forum.opentap.io/u/lucappelman)\
**Post date:** [December 3, 2021, 10:52am UTC](https://forum.opentap.io/t/refresh-available-ports/540/3 "2021-12-03T10:52:18Z")

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Thanks for your reply.

I tried you solution and the list is updated while the OpenTAP is running but unfortunately it does not update when I click the dropdown. It does update when opening the instrument menu, and changing the value (or any other value in the instrument). And the `get` function is called 5 times, which seems a little unnecessary, but I think there’s nothing we can do about that (except creating a debounce).

Any chance you know another solution?

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<div class="post-metadata">

**Author:** ![rolf\_madsen](https://avatars.discourse-cdn.com/v4/letter/r/43a26b/32.png) [@rolf\_madsen](https://forum.opentap.io/u/rolf_madsen)\
**Post date:** [December 3, 2021, 1:36pm UTC](https://forum.opentap.io/t/refresh-available-ports/540/4 "2021-12-03T13:36:03Z")

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It may be a bit simplistic, but I’d recommend creating a button in the UI to update the values. This way the user knows what to expect and you don’t create performance issues.

```cs
[Display(/*...*/)]
[Browsable(true)]
public void RefreshAvailablePorts(){
   mAvailablePorts = new List<string>( SerialPort.GetPortNames());
}

```

---

<div class="post-metadata">

**Author:** ![lucappelman](https://avatars.discourse-cdn.com/v4/letter/l/e274bd/32.png) [@lucappelman](https://forum.opentap.io/u/lucappelman)\
**Post date:** [December 3, 2021, 1:59pm UTC](https://forum.opentap.io/t/refresh-available-ports/540/5 "2021-12-03T13:59:47Z")

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That’s a great idea. However, it will not call the getter to update the list in the UI.

I have done some more digging and found out even when forcefully updating the list using a timer the showed values in the UI will not update. Only when the menu is reloaded (by opening it) or a value is changed new values show. So it seems OpenTAP creates a complete copy of the class to display the menu and only gets new values when changes are made using the interface.

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<div class="post-metadata">

**Author:** ![rolf\_madsen](https://avatars.discourse-cdn.com/v4/letter/r/43a26b/32.png) [@rolf\_madsen](https://forum.opentap.io/u/rolf_madsen)\
**Post date:** [December 3, 2021, 3:15pm UTC](https://forum.opentap.io/t/refresh-available-ports/540/6 "2021-12-03T15:15:12Z")

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Ah you are right, button click does not automatically ensure a gui update. This seems like a mistake.

You can force it by calling ValidatingObject.OnPropertyChanged (so this should work on your object as well.) e.g:

```cs
[Display(/*...*/)]
[Browsable(true)]
public void RefreshAvailablePorts(){
   mAvailablePorts = new List<string>( SerialPort.GetPortNames());
 // force the GUI to reload settings values.
  OnPropertyChanged(nameof(mAvailablePorts));
}

```

Be a bit careful with OnPropertyChanged. It can affect UI performance if called too often.

---

<div class="post-metadata">

**Author:** ![lucappelman](https://avatars.discourse-cdn.com/v4/letter/l/e274bd/32.png) [@lucappelman](https://forum.opentap.io/u/lucappelman)\
**Post date:** [December 6, 2021, 10:50am UTC](https://forum.opentap.io/t/refresh-available-ports/540/7 "2021-12-06T10:50:44Z")

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This works, thank you!