Long delay before displaying items (Combobox)

[washburnit]

Hi,

I have a Combobox that is loaded with about 1300 items.
Items are read from a SQL table, loaded into a "class" with two elements and then assigned as "ItemSource" to the Combobox.
Apparently loading all the items is very fast but when I click on the combobox to open the list, it takes about 5/6 seconds to display the items.
Maybe I'm loading the combo in the wrong way, but the same "issue" occurs even if I load simple strings.
That is XAML and code behind:

<ComboBox x:Name="cbCli" Style="{StaticResource MaterialDesignOutlinedComboBox}" mdix:HintAssist.Hint="Ricerca Cliente" mdix:HintAssist.HintOpacity=".26" IsEditable="True" Width="500" FontFamily="Century Gothic" FontSize="15" Margin="20,20,0,0" HorizontalAlignment="Left"/>
`

       private class DatiCli
       {
             public UInt32 IDc { get; set; }
             public String ragSoc { get; set; }
       }

      //********* CODE TO LOAD THE COMBOBOX ***************//
       String str="";
       UInt32 IDc=0; 
       DatiCli DC= new DatiCli; 
       DatiCli lDC = new List<DatiCli>();

        while (PQuery.Read())
        {
            //ComboboxItem cbItem = new ComboboxItem();
            DC = new DatiCli();
            IDc = Convert.ToUInt32(PQuery["ID"]);
            str = PQuery["RAGIONESOCIALE"].ToString();
            DC.IDc = IDc;
            DC.ragSoc = str;
            lDC.Add(DC);                
        }

        cbCli.ItemsSource = lDC;
        cbCli.DisplayMemberPath = "ragSoc";
        cbCli.SelectedValuePath = "IDc";

`

I noticed that with a "standard" combobox (in a "non wpf" program) the combobox doesn't have any delay.
Thank you, regards.

Roberto

[Keboo]

Thanks Roberto, this sounds like a data virtualization issue. Looking over the code it appears that this library does not have virtualization enabled by default (this is a bug that should get fixed).
In the meantime you should be able to follow the virtualized ComboBoxes from the demo app to enabled virtualization.

                <ComboBox
                    materialDesign:HintAssist.Hint="Virtualisation"
                    MinWidth="72"
                    ItemsSource="{Binding LongListToTestComboVirtualization}"
                    SelectedValue="{Binding SelectedValueOne}">

                    <ComboBox.SelectedItem>
                        <Binding
                            Path="SelectedValueOne"
                            Mode="TwoWay"
                            UpdateSourceTrigger="PropertyChanged">
                            <Binding.ValidationRules>
                                <demoAppDomain:NotEmptyValidationRule
                                    ValidatesOnTargetUpdated="True" />
                            </Binding.ValidationRules>
                        </Binding>
                    </ComboBox.SelectedItem>
                    
                    <ComboBox.ItemsPanel>
                        <ItemsPanelTemplate>
                            <VirtualizingStackPanel />
                        </ItemsPanelTemplate>
                    </ComboBox.ItemsPanel>
                </ComboBox>

[ElieTaillard]

Issue created: #2725

[washburnit]

Thanks Keboo, your suggestion fixed the issue.
Regards,

Roberto