How to refresh Combobox Items at Runtime when Combobox Itemsource is binded to a List in WPF?

Question

How to refresh Combobox Items at Runtime when Combobox Itemsource is binded to a List in WPF?

MERUN KUMAR MAITY 636

Hi there, I have a WPF application where I use a ComboBox. My ComboBox ItemSource is bind to a List <> which I populate from C# in background.

Here is the C# code of that List<> :

// Main code  
         List<AudioDevice> devices = new List<AudioDevice>();  
     HRESULT hr = HRESULT.E_FAIL;  
     Guid CLSID_MMDeviceEnumerator = new Guid("{BCDE0395-E52F-467C-8E3D-C4579291692E}");  
     Type MMDeviceEnumeratorType = Type.GetTypeFromCLSID(CLSID_MMDeviceEnumerator, true);  
     object MMDeviceEnumerator = Activator.CreateInstance(MMDeviceEnumeratorType);  
     IMMDeviceEnumerator pMMDeviceEnumerator = (IMMDeviceEnumerator)MMDeviceEnumerator;  
     if (pMMDeviceEnumerator != null)  
     {  
         string sIdDefaultRender = null;  
         string sIdDefaultCapture = null;  
         IMMDevice pDefaultDevice = null;  
         hr = pMMDeviceEnumerator.GetDefaultAudioEndpoint(EDataFlow.eRender, ERole.eConsole, out pDefaultDevice);  
         if (hr == HRESULT.S_OK)  
         {  
             IntPtr hGlobal = Marshal.AllocHGlobal(260);  
             hr = pDefaultDevice.GetId(out hGlobal);  
             sIdDefaultRender = Marshal.PtrToStringUni(hGlobal);  
             Marshal.FreeHGlobal(hGlobal);  
             Marshal.ReleaseComObject(pDefaultDevice);  
         }  
         hr = pMMDeviceEnumerator.GetDefaultAudioEndpoint(EDataFlow.eCapture, ERole.eConsole, out pDefaultDevice);  
         if (hr == HRESULT.S_OK)  
         {  
             IntPtr hGlobal = Marshal.AllocHGlobal(260);  
             hr = pDefaultDevice.GetId(out hGlobal);  
             sIdDefaultCapture = Marshal.PtrToStringUni(hGlobal);  
             Marshal.FreeHGlobal(hGlobal);  
             Marshal.ReleaseComObject(pDefaultDevice);  
         }  
         IMMDeviceCollection pDeviceCollection = null;  
         hr = pMMDeviceEnumerator.EnumAudioEndpoints(EDataFlow.eAll, DEVICE_STATE_ACTIVE | DEVICE_STATE_UNPLUGGED, out pDeviceCollection);  
         if (hr == HRESULT.S_OK)  
         {  
             uint nDevices = 0;  
             hr = pDeviceCollection.GetCount(out nDevices);  
             devices.Add(new AudioDevice() { Name = "System default", Direction = "Playback", Id = sIdDefaultRender, Default = true });  
             for (uint i = 0; i < nDevices; i++)  
             {  
                 IMMDevice pDevice = null;  
                 hr = pDeviceCollection.Item(i, out pDevice);  
                 if (hr == HRESULT.S_OK)  
                 {  
                     IPropertyStore pPropertyStore = null;  
                     hr = pDevice.OpenPropertyStore(STGM_READ, out pPropertyStore);  
                     if (hr == HRESULT.S_OK)  
                     {  
                         string sFriendlyName = null;  
                         string sDesc = null;  
                         PROPVARIANT pv = new PROPVARIANT();  
                         hr = pPropertyStore.GetValue(ref PKEY_Device_FriendlyName, out pv);  
                         if (hr == HRESULT.S_OK)  
                         {  
                             sFriendlyName = Marshal.PtrToStringUni(pv.pwszVal);  
                         }  
                         hr = pPropertyStore.GetValue(ref PKEY_Device_DeviceDesc, out pv);  
                         if (hr == HRESULT.S_OK)  
                         {  
                             sDesc = Marshal.PtrToStringUni(pv.pwszVal);  
                         }  
                         IntPtr hGlobal = Marshal.AllocHGlobal(260);  
                         hr = pDevice.GetId(out hGlobal);  
                         string sId = Marshal.PtrToStringUni(hGlobal);  
                         Marshal.FreeHGlobal(hGlobal);  
                         IMMEndpoint pEndpoint = null;  
                         pEndpoint = (IMMEndpoint)pDevice;  
                         EDataFlow eDirection = EDataFlow.eAll;  
                         hr = pEndpoint.GetDataFlow(out eDirection);  
                         //System.Diagnostics.Trace.WriteLine("\tDirection : " + eDirection.ToString());  
                         string sDirection = "";  
                         if (eDirection == EDataFlow.eRender)  
                             sDirection = "Playback";  
                         else if (eDirection == EDataFlow.eCapture)  
                             sDirection = "Recording";  
                         int nState = 0;  
                         hr = pDevice.GetState(out nState);  
                         if ((nState == DEVICE_STATE_ACTIVE))  
                         {  
                             devices.Add(new AudioDevice() { Name = sFriendlyName, Direction = sDirection, Id = sId, Default = (sId == sIdDefaultRender || (sId == sIdDefaultCapture)) });  
                             //sFriendlyName += (sId == sIdDefaultRender || sId == sIdDefaultCapture) ? " (System default)" : "";  
                             //devices.Add(new AudioDevice() { Name = sFriendlyName, Direction = sDirection, Default = (sId == sIdDefaultRender || (sId == sIdDefaultCapture)) });  
                             ////devices.Add(new AudioDevice() { Name = sFriendlyName, Direction = sDirection, Default = (sId == sIdDefaultRender || (sId == sIdDefaultCapture)) });  
                         }  
                         Marshal.ReleaseComObject(pPropertyStore);  
                     }  
                     Marshal.ReleaseComObject(pDevice);  
                 }  
             }  
             devices.Insert(devices.Count - 0, new AudioDevice() { Name = "Selected application ...", Direction = "Recording", Id = "Idlast", Default = false });  
         }  
         Marshal.ReleaseComObject(pDeviceCollection);  
         ListCollectionView lcv = new ListCollectionView(devices);  
         lcv.GroupDescriptions.Add(new PropertyGroupDescription("Direction"));  
         this.cmb1.ItemsSource = lcv;  
     }  
 }  
 public class AudioDevice  
         {  
             public string Name { get; set; }  
             public string Direction { get; set; }  
             public string Id { get; set; }  
             public bool Default { get; set; }  
      
         }

If you carefully see the code then You see this line this.cmb1.ItemsSource = lcv; That means the List<> is added as ItemSource of the ComboBox, Now, I have a control template for comboBoxItem, my ComboBoxitem control template have lots of visual customisation and effects according to my choice.

Here is my ComboBoxItem controltemplate :

<Style x:Key="ItemStyleOne" TargetType="{x:Type ComboBoxItem}">  
             <Setter Property="SnapsToDevicePixels" Value="True"/>  
             <Setter Property="UseLayoutRounding" Value="True"/>  
             <Setter Property="RenderOptions.BitmapScalingMode" Value="NearestNeighbor"/>  
             <Setter Property="RenderOptions.ClearTypeHint" Value="Enabled"/>  
             <Setter Property="Template">  
                 <Setter.Value>  
                     <ControlTemplate TargetType="{x:Type ComboBoxItem}">  
                         <Grid>  
                             <Border x:Name="gd" Background="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ComboBox}},Path=Background}" BorderThickness="0" SnapsToDevicePixels="True" UseLayoutRounding="True" RenderOptions.BitmapScalingMode="NearestNeighbor" RenderOptions.ClearTypeHint="Enabled">  
                                 <ContentPresenter  
                                 Name="ContentSite" Margin="25, 3, 0, 11" VerticalAlignment="Center">  
                                     <ContentPresenter.ContentTemplate>  
                                     <DataTemplate>  
                                          <TextBlock SnapsToDevicePixels="True" UseLayoutRounding="True" RenderOptions.BitmapScalingMode="HighQuality" RenderOptions.EdgeMode="Aliased">  
                                                
                                                 <Run Text="{Binding Name}"/>  
                                             </TextBlock>  
                                     </DataTemplate>  
                                 </ContentPresenter.ContentTemplate>  
                                 </ContentPresenter>  
                             </Border>  
                             <Rectangle x:Name="Border1" Width="12" Height="10" Margin="-220,-7,0,0"          RenderOptions.BitmapScalingMode="HighQuality" RenderOptions.ClearTypeHint="Auto" SnapsToDevicePixels="True" RenderOptions.EdgeMode="Unspecified">  
                                 <Rectangle.Fill>  
                                     <DrawingBrush>  
                                         <DrawingBrush.Drawing>  
                                             <DrawingGroup>  
                                                 <DrawingGroup.Children>  
                                                     <GeometryDrawing Brush="#d0021b" Geometry="M95.118,21.399L86.601,12.882C85.422,11.703,83.523,11.703,82.344,12.882L38.799,58.854 13.839,33.882C12.648,32.691,10.716,32.691,9.52499999999999,33.882L0.896999999999991,42.516C-0.294000000000009,43.704,-0.294000000000009,45.636,0.896999999999991,46.83L36.396,83.154C37.083,83.844 38.016,84.081 38.913,83.964 39.84,84.102 40.806,83.868 41.517,83.154L95.118,25.659C96.294,24.483,96.294,22.575,95.118,21.399z">  
                                                         <GeometryDrawing.Pen>  
                                                             <Pen LineJoin="Round" Brush="#d0021b" Thickness="2.5"/>  
                                                         </GeometryDrawing.Pen>  
                                                     </GeometryDrawing>  
                                                 </DrawingGroup.Children>  
                                             </DrawingGroup>  
                                         </DrawingBrush.Drawing>  
                                     </DrawingBrush>  
                                 </Rectangle.Fill>  
                             </Rectangle>  
                         </Grid>  
                         <ControlTemplate.Triggers>  
                             <Trigger Property="ComboBoxItem.IsMouseOver" Value="True">  
                                 <Setter TargetName="gd" Property="Background" Value="#3c3c3c"></Setter>  
                                 <Setter TargetName="gd" Property="TextElement.Foreground" Value="#ffffff"></Setter>  
                                 <Setter TargetName="gd" Property="SnapsToDevicePixels" Value="True"/>  
                                 <Setter TargetName="gd" Property="UseLayoutRounding" Value="True"/>  
                                 <Setter TargetName="gd" Property="RenderOptions.BitmapScalingMode" Value="NearestNeighbor"/>  
                                 <Setter TargetName="gd" Property="RenderOptions.ClearTypeHint" Value="Enabled"/>  
                                 <Setter TargetName="Border1" Property="Visibility" Value="Collapsed"/>  
                             </Trigger>  
                             <Trigger Property="ComboBoxItem.IsMouseOver" Value="False">  
                                 <!--<Setter TargetName="gd" Property="Background" Value="#3c3c3c"></Setter>  
                                 <Setter TargetName="gd" Property="TextElement.Foreground" Value="#ffffff"></Setter>  
                                 <Setter TargetName="gd" Property="SnapsToDevicePixels" Value="True"/>  
                                 <Setter TargetName="gd" Property="UseLayoutRounding" Value="True"/>  
                                 <Setter TargetName="gd" Property="RenderOptions.BitmapScalingMode" Value="NearestNeighbor"/>  
                                 <Setter TargetName="gd" Property="RenderOptions.ClearTypeHint" Value="Enabled"/>-->  
                                 <Setter TargetName="Border1" Property="Visibility" Value="Hidden"/>  
                             </Trigger>  
                             <Trigger Property="ComboBoxItem.IsSelected" Value="True">  
                                 <Setter TargetName="Border1" Property="Visibility" Value="Visible"/>  
                                 <!--<Setter TargetName="gd" Property="SnapsToDevicePixels" Value="True"/>  
                                 <Setter TargetName="gd" Property="UseLayoutRounding" Value="True"/>  
                                 <Setter TargetName="gd" Property="RenderOptions.BitmapScalingMode" Value="NearestNeighbor"/>  
                                 <Setter TargetName="gd" Property="RenderOptions.ClearTypeHint" Value="Enabled"/>-->  
                             </Trigger>  
                         </ControlTemplate.Triggers>  
                     </ControlTemplate>  
                 </Setter.Value>  
             </Setter>  
         </Style>

After adding this controltemplate in my ComboBoxitem my comboBox looks amazing. This is how I add this ComboBoxItem Style="{StaticResource ItemStyle}" ,

The code I given, is to show available audio devices in a computer systems.

But in this case my ComboBox content is added from a List<> not from a ComboBox item, all of my code is perfect and I can run successfully.

But my problem is, my ComboBox can not refresh at run time. I give an example, suppose I have three audio devices and I run my Application, my application successfully detect the three devices but If I add more devices at that time, suppose I add two more devices that means total five devices but still my application is showing three devices but it only showing five devices if I restart my application.

How Can I refresh that? I know that, updating and refreshing ComboBox is too much easy, if my Combobox Item source is binded from a ViewModel and if I implement INotifyPropertyChanged event there, but in my case the ComboBox item source is from a List<>. That's why it's too much difficult.

Peter Fleischer (former MVP) 19,341 Reputation points

2022-12-26T05:52:47.353+00:00

Hi,
instead if List<AudioDevice> use ObservableCollection<AudioDevice> an instead if "this.cmb1.ItemsSource = lcv;" use property and Binding.
MERUN KUMAR MAITY 636 Reputation points

2022-12-26T15:40:31.16+00:00

Thank you very much for your reply. Can you please give me the answer with full source code? if you do then I definitely accept your answer.
Hui Liu-MSFT 48,711 Reputation points Microsoft External Staff

2022-12-27T02:02:01.513+00:00

Hi, @MERUN KUMAR MAITY . Have you checked my answer to see if it meets your requirements? I have the complete code in my answer.
MERUN KUMAR MAITY 636 Reputation points

2022-12-27T14:25:14.233+00:00

Thank you very much sir, for your valuable answer but I can not understand your code because your code is not totally complete..it's partially completed. Should I put my default List<AudioDevice> code in if (flag != null) statement block? I know my question is very childish to you but I am very weak in C#. Kindly complete the full source code, don't leave anything..give proper comment documentation so, that I can accept your answer.

Answer accepted by question author

1 additional answer

Your answer

Peter Fleischer (former MVP) 19,341 Reputation points

2022-12-26T05:52:47.353+00:00

Hi,
instead if List<AudioDevice> use ObservableCollection<AudioDevice> an instead if "this.cmb1.ItemsSource = lcv;" use property and Binding.
MERUN KUMAR MAITY 636 Reputation points

2022-12-26T15:40:31.16+00:00

Thank you very much for your reply. Can you please give me the answer with full source code? if you do then I definitely accept your answer.
Hui Liu-MSFT 48,711 Reputation points Microsoft External Staff

2022-12-27T02:02:01.513+00:00

Hi, @MERUN KUMAR MAITY . Have you checked my answer to see if it meets your requirements? I have the complete code in my answer.
MERUN KUMAR MAITY 636 Reputation points

2022-12-27T14:25:14.233+00:00

Thank you very much sir, for your valuable answer but I can not understand your code because your code is not totally complete..it's partially completed. Should I put my default List<AudioDevice> code in if (flag != null) statement block? I know my question is very childish to you but I am very weak in C#. Kindly complete the full source code, don't leave anything..give proper comment documentation so, that I can accept your answer.

Answer 1

Peter Fleischer (former MVP) 19,341

Hi,
use instead of new instance of list in every update the same instance of list in every update.

MERUN KUMAR MAITY 636 Reputation points

2022-12-26T19:35:16.603+00:00

Thank you very much, I understand the theory but if you complete your code, so that I can fully understand it. By the way, your answer is brilliant, because most of the time in this situation people rush to implement the INotifyPropertyChanged event but your trick is awesome.

Kindly complete your code and give me proper instruction so that I can accept your answer.

Peter Fleischer (former MVP) 19,341

Hi,
another way is to use binding. If you use ObservableCollection INotifyPropertyChanged is not nessecary.:

<Window x:Class="WpfApp1.Window038"  
...  
  <StackPanel>  
    <Button Content="Next Device" Margin="10" Click="Update"/>  
    <ComboBox Margin="10" ItemsSource="{Binding Devices}"/>  
  </StackPanel>  
</Window>  
  
	public partial class Window038 : Window  
	{  
		public Window038()  
		{  
			InitializeComponent();  
			this.DataContext = this;  
			cvs.Source = devices;  
		}  
  
		ObservableCollection<AudioDevice> devices = new ObservableCollection<AudioDevice>();  
		private CollectionViewSource cvs = new CollectionViewSource();  
  
		public ICollectionView Devices { get => cvs.View; }  
  
		private void Update(object sender, RoutedEventArgs e)  
		{  
			// Main code  
... your code  
          Marshal.ReleaseComObject(pDeviceCollection);  
          // ListCollectionView lcv = new ListCollectionView(devices);  
          // lcv.GroupDescriptions.Add(new PropertyGroupDescription("Direction"));  
          // this.cmb1.ItemsSource = lcv;  
...

MERUN KUMAR MAITY 636 Reputation points

2022-12-27T15:35:46.223+00:00

Your code is not working..
Peter Fleischer (former MVP) 19,341 Reputation points

2022-12-27T17:11:55.05+00:00

Hi,
the demo works for me. I don't know what did you do.
MERUN KUMAR MAITY 636 Reputation points

2023-02-08T18:54:15.8+00:00

Hi, I love your first option where you try to update the list, Can update the full code so, that I can taste it and if it's working then I can accept your answer.
MERUN KUMAR MAITY 636 Reputation points

2023-02-25T20:02:59.0766667+00:00

Dear sir, finally I solved my problem by using your first method where you say

use instead of new instance of list in every update the same instance of list in every update.

But I have one last question? Can you please reply.
Peter Fleischer (former MVP) 19,341 Reputation points

2023-02-26T05:54:22.9433333+00:00

Which last question? Please, start new thread.

Answer 2

Hui Liu-MSFT 48,711 Microsoft External Staff

You could use ObservableCollection<AudioDevice> instead of List. And implement the INotifyPropertyChanged interface to complete the view update.
Here is an example made with reference to your code, you can refer to it. The button in it simulates a collection update.

Xaml:

  <StackPanel>  
        <Button x:Name="btn" Click="btn_Click" Height="30" Content=" add item"/>  
        <ComboBox  x:Name="cmb1" Width="200" Height="60" ItemContainerStyle="{StaticResource ItemStyleOne}" />  
    </StackPanel>

Codebehind:

273946-icollectionview.txt

The result:

----------------------------------------------------------------------------

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MERUN KUMAR MAITY 636 Reputation points

2022-12-27T17:43:23.68+00:00

Thank you very much sir, for your valuable answer but I can not understand your code because your code is not totally complete..it's partially completed. Should I put my default List<AudioDevice> code in if (flag != null) statement block? I know my question is very childish to you but I am very weak in C#. Kindly complete the full source code, don't leave anything..give proper comment documentation so, that I can accept your answer.
Hui Liu-MSFT 48,711 Reputation points Microsoft External Staff

2023-01-31T09:20:59.83+00:00

Hi，@MERUN KUMAR MAITY . I think so. In my code, flag is used to count the ComBoxItems that are added. You could use your way to distinguish each newly added ComBoxItem.

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How to refresh Combobox Items at Runtime when Combobox Itemsource is binded to a List in WPF?

1 additional answer

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