I try to bind a ComboBox to a collection:
<ComboBox Margin="4 0 2 0"
ItemsSource="{Binding YAxes}"
SelectedItem="{Binding SelectedYAxis, Mode=TwoWay}"
DisplayMemberPath="AxisTitle"
SelectedValuePath="AxisTitle"/>
Everything is fine, except Text of this ComboBox. On selection of item, the setter on SelectedYAxis fires and notifies, that property has been changed:
private IAxis _selectedYAxis;
public IAxis SelectedYAxis
{
get => _selectedYAxis;
set
{
_selectedYAxis = value;
OnPropertyChanged(nameof(SelectedYAxis));
}
}
but the text on ComboBox never changes to the selected items AxisTitle. How to display an AxisTitle of SelectedItem as a text of ComboBox?
UPD: Text is never shown, even if it's set explicitly:
<ComboBox Margin="4 0 2 0"
ItemsSource="{Binding XAxes}"
SelectedItem="{Binding SelectedXAxis, Mode=TwoWay}"
DisplayMemberPath="AxisTitle"
Text="Asdasd"/>
It doesn't set the text of ComboBox to "Asdasd".
UPD 2: I've changed the things to use DataTemplate, but this didn't work as well:
<ComboBox Margin="4 0 2 0"
ItemsSource="{Binding YAxes}"
SelectedItem="{Binding SelectedYAxis, Mode=TwoWay}"
ItemTemplate="{StaticResource AxisCBTextTemplate}"/>
And the resource section above:
<DataTemplate x:Key="AxisCBTextTemplate">
<TextBlock Text="{Binding AxisTitle}"/>
</DataTemplate>
UPD 3
An illustration to what do I mean:
The task of displaying some selected text should be trivial, but it has difficulties.
I've found the root cause of this issue. Each IAxis (it is a SciChart axis object) from XAxes and YAxes is already dispayed on the graph (i.e. bound). Binding them to other controls (like ListBox) causes an exception: "Must disconnect specified child from current parent Visual before attaching to new parent Visual.", I found it out while trying to bind them to ListBox.
Seemes like ComboBox catches such exceptions and doesn't output StackTrace for any case. In my case this exception was wrapped into NullReferenceException and occurred only on click on a ComboBox, that has no ItemTemplate set. Though I may not be fully correct in details, replacing XAxes and YAxes with collections of strings solves this issue.
Related
I have a ComboBox in WPF. The ComboBox is inside of a grid, and the grid's DataContext is bound to the SelectedItem of a ListView. The ItemsSource of the ComboBox is set to a StaticResource, located in the window resources. The ItemsSource does not change. I have tried to use both SelectedValue and SelectedItem but both of them cause the same issue for me. The issue is that when the SelectedItem of the ListView is changed, the ComboBox is actually setting the property value from the PREVIOUSLY selected item, to the property value of the NEWLY selected item. Clearly I am doing something wrong, because I have used comboboxes many times in the past without this issue. I have scoured the web and can't find an answer. The closest, most similar question I found was: Strange behaviour (or bug?) with ComboBox in WPF when changing DataContext and having bound ItemsSource and SelectedItem
But it doesn't seem to have a solution. The solutions listed in comments did not work for me.
I created SelectionChanged events for both the ListView and the ComboBox and set breakpoints at each of them and the property that is being set. The property is actually being set BEFORE either one of those are triggered. So even if I wanted to create some hack workaround, I couldn't.
For the record, the ComboBox functionality works perfectly fine. When an object is selected in the ListView, I can see the Template name property, as I should, and the list of items is correct. If I manually change the selected item, the property is changed to a new item, just like it should. The problem is that when I change the selected item in the ListView, the "Template" property of the newly selected object is being set to the "Template" property of the previously selected object. So the combobox is changing before anything else.
The xaml for the ListView and ComboBox are below.
<ListView x:Name="my_ListBox" FlowDirection="RightToLeft"
Margin="5" Grid.RowSpan="2" SelectedIndex="0"
ItemsSource="{Binding Source={StaticResource myList}}"
DisplayMemberPath="Name"
SelectionChanged="my_ListBox_SelectionChanged"/>
<Grid DataContext="{Binding ElementName=my_ListBox, Path=SelectedItem}">
<ComboBox Name="comboBox_myTemplate"
ItemsSource="{Binding Source={StaticResource myTemplatesList}}"
SelectedValue="{Binding Template}"
SelectionChanged="comboBox_myTemplate_SelectionChanged"
DisplayMemberPath="Name" FontSize="20" Margin="5"/>
</Grid>
If I set "IsSynchronizedWithCurrentItem="True"" in the ComboBox the problem is resolved. If someone wants to explain what exactly that is doing and how it works I'd love to hear it. Thanks.
I am working on a WPF Application where i have a combobox with ItemsSource binded to a property of 5000 records coming from database. The problem is that when i click the dropdown arrow of combobox the UI not responding or combobox is taking too much time to respond. I searched it but nothing worked for me.
here is the code:
<ComboBox IsEditable="True" ItemsSource="{Binding List,Mode=OneWay}" DisplayMemberPath="name" SelectedValue="{Binding SelectedItem,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}">
<ComboBox.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel VirtualizingStackPanel.IsVirtualizing="True" VirtualizingStackPanel.VirtualizationMode="Recycling" />
</ItemsPanelTemplate>
</ComboBox.ItemsPanel>
</ComboBox>
and the property
private ObservableCollection<Object> _List = new ObservableCollection<Object>();
public ObservableCollection<Object> List
{
get { return _List ; }
set { _List = value; OnPropertyChanged("List"); }
}
Edit:
here is the code that loads data inside the constructor
public FormVM()
{
List = new ObservableCollection<Object>(db.cat.ToList());
}
You have to enable UI virtualization.
Currently UI virtualization is disabled for your ComboBox!
Controls like ListBox or ListView have this feature enabled by default.
Other controls that extend ItemsControl like ComboBox have to enable it explicitly.
To enable UI virtualization
The ItemsPresenter (or any Panel with Panel.IsItemsHost set to True) of the ItemsControl must be the child of a ScrollViewer.
This is already the case for the ComboBox.
The ScrollViewer must be configured to scroll by items (logical units) instead of pixels (physical units) by setting the attached ScrollViewer.CanContentScroll property to True.
ItemsControl must have its ItemsPanel set to a VirtualizingStackPanel.
The virtualization mode of the VirtualizingPanel must be enabled by setting the attached property VirtualizingPanel.IsVirtualizing to True.
Example
<ComboBox VirtualizingPanel.IsVirtualizing="True"
ScrollViewer.CanContentScroll="True">
<ComboBox.ItemsPanel>
<ItemsPanelTemplate>
<VirtualizingStackPanel />
</ItemsPanelTemplate>
</ComboBox.ItemsPanel>
</ComboBox>
Further improvements can be achieved by enabling deferred scrolling:
<ComboBox ScrollViewer.IsDeferredScrollingEnabled="True" />
Satisfying one of the following conditions will make UI virtualization impossible:
Item containers are added directly to the ItemsControl. For example,
if an application explicitly adds ListBoxItem objects to a ListBox,
the ListBox does not virtualize the ListBoxItem objects.
Item containers in the ItemsControl are of different types. For
example, a Menu that uses Separator objects cannot implement item
recycling because the Menu contains objects of type Separator and
MenuItem.
Setting CanContentScroll to false.
Setting IsVirtualizing to false.
If you have followed every constraint then UI virtualization does work. You then have a problem which is not related to UI virtualization. If yoou would set up a new empty project with just a ComboBox you should encounter no issues.
I have a collection of Contact objects that I've bound as follows in a WPF form:
<ComboBox Name="Name"
Text="{Binding Path=Contact.FullName}"
ItemsSource="{Binding ContactsCollection}"
SelectedItem="{Binding Path=Contact, Mode=TwoWay}"
IsEditable="true"
IsTextSearchEnabled="True"
TextBoxBase.TextChanged="Name_TextChanged"/>
<TextBox Name="Position" Text="{Binding Path=Contact.Position}"/>
<TextBox Name="Phone" Text="{Binding Path=Contact.PhoneNumber}"/>
I'd like the contact to be selected when the user starts typing in the combo 'IsTextSearchEnabled=true'.
The problem is that I'd like the items in the collection to remain read-only. Once a contact has been selected, any text deletes or additions modify the contact name in the collection.
How can I bind a collection to a combobox, enable search and prevent edits to the collection?
I could be missing something here, but if you don't want an editable ComboBox, try not setting the ComboBox.IsEditable property to True. Using this simple code, I can display items in a ComboBox and make selections by typing (when the ComboBox is focused) without editing anything:
<ComboBox ItemsSource="{Binding Items}" IsTextSearchEnabled="True" Height="25" />
Thanks for your input. It sorted me out. Removing the SelectedItem property and setting Position and PhoneNumber in the PropertyChanged event was what I needed.
i am trying to set selected item through following code but its not working:
<StackPanel Orientation="Horizontal">
<TextBlock Text="Sort by" Margin="10" VerticalAlignment="Center"/>
<ComboBox Width="{StaticResource ComboWidth}" x:Name="sortcombo" ItemsSource="{Binding Path=SortOrder}" SelectionChanged="SearchCombo_SelectionChanged" SelectedItem="{Binding Path=DefaultSortIndex}">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=Sort}"/>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
</StackPanel>
however it works fine if i use selectedIndex instead with binding to 0th index. Any thing wrong with declaration?
By the name of your property DefaultSortIndex maybe you are trying to bind an int for SelectedItem.
SeletedItem refers to an element of your collection binded to ItemsSource, so the property binded to SelectedItem must be of type of your collection elements.
If you bind int value to selected item then it will not work, you should bind element for that. For int value you can set it as mentioned in following post :
Set Selected Item of WPF Combobox to User Setting
found out the issue, actually the data source was creating new list everytime I call getData().
I'm new to WPF/C#, and I'm trying to create a simple sql query application to get used to it. I have a listbox and a corresponding button in my XAML:
<ListBox Name="dbTables" Grid.Column="1" Grid.Row="2">
<ListBoxItem>Log</ListBoxItem>
<ListBoxItem>DownloadRequest</ListBoxItem>
<ListBoxItem>EmailRequest</ListBoxItem>
</ListBox>
<!-- View report button -->
<Button x:Name="myButton" Grid.Column="1" Grid.Row="3" Margin="0,10,0,0" Width="125" Height="25" HorizontalAlignment="Right" Click="Button_Click">View</Button>
and the corresponding C# function:
private void Button_Click(object sender, RoutedEventArgs e)
{
String curItem = dbTables.SelectedValue.ToString();
Console.WriteLine("CurItem = " + curItem);
Results resultsPage = new Results(curItem);
this.NavigationService.Navigate(resultsPage);
}
However, when it outputs the CurItem it has this value:
CurItem = System.Windows.Controls.ListBoxItem: Log
Which then throws an exception when I try to run a SQL Query. I'm trying to get it to just be
CurItem = Log
I've tried several different ways but I can't seem to just get the name of the selected value without the object definition attached.
SelectedItem returns the currently selected item in the list box. Since you're populating your list box with ListBoxItems, that's what it will return. (Note, by the way, that your list box automatically generates ListBoxItem containers for its items - if you look in the visual tree, you'll find that this ListBox contains ListBoxItems, each of which contains a ListBoxItem. SelectedItem contains the content of the generated ListBoxItem, which is to say the ListBoxItem you're creating in markup.)
SelectedValue returns the value of the property of SelectedItem that is specified by ListBox.SelectedValuePath. If no SelectedValuePath is given, it returns SelectedItem, so if you don't know about SelectedValuePath, it seems like the two are the same thing. But if you populate your list with, say, Person objects, and set SelectedValuePath to "Name", the SelectedValue will contain the selected person's name, not a reference to the Person object.
So in your example, you can make SelectedValue return the string by setting SelectedValuePath to "Content", which is the property of the ListBoxItem that contains the strings you're using.
You can do it another way by not explicitly creating ListBoxItems and just populating the ListBox with strings. You have to declare a namespace referencing mscorlib to do this, so that you can represent string objects in XAML, but once you do, the result's simple:
<Page
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:sys="clr-namespace:System;assembly=mscorlib">
<DockPanel>
<ListBox DockPanel.Dock="Top" Margin="10" x:Name="test" SelectedValuePath="Length">
<sys:String>Log</sys:String>
<sys:String>DownloadRequest</sys:String>
<sys:String>EmailRequest</sys:String>
</ListBox>
<TextBlock DockPanel.Dock="Top" Margin="10" Text="{Binding ElementName=test, Path=SelectedItem}"/>
<TextBlock DockPanel.Dock="Top" Margin="10" Text="{Binding ElementName=test, Path=SelectedValue}"/>
</DockPanel>
</Page>
The Selected Value is a ListBoxItem, so you can cast the value to ListBoxItem, and then use the Content property:
ListBoxItem selItem = (ListBoxItem)dbTables.SelectedValue;
Console.WriteLine(selItem.Content);
String curItem = (dbTables.SelectedValue as ListBoxItem).Content.ToString();