I am new to WPF:
I have a combobox whose ItemsSource is changing. This is not being reflected back to the user. Do i have to specify the ItemsSource Mode to TwoWay?
Any Suggessions?
<ComboBox Height="Auto" Name="comboBoxQuery" Width="300" IsEditable="True" ItemsSource="{Binding QueryNames, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" SelectedItem="{Binding SelectedQueryNames, Mode=TwoWay}" SelectedValuePath="Key" DisplayMemberPath="Value" Visibility="Collapsed" /> <!--Is this correct? -->
In order to tell the view that collection source was changed, you should use collection classes which supports INotifyCollectionChanged interface. For example: ObservableCollection, BindingList. You do not need TwoWay data binding, WPF will detect that source collection supports INotifyCollectionChanged interface, and all changes you made in that collection will reflect the view.
Related
I'm currently trying to do some binding inside of a datagrid but I'm having problems getting up to the level of DataContext of the view.
Here is the code:
<DataGridTemplateColumn.CellEditingTemplate>
<DataTemplate>
<ComboBox SelectedItem="{Binding Operators}"
ItemsSource="{Binding DataContext.OperatorList,ElementName=FilterGrid}" />
</DataTemplate>
</DataGridTemplateColumn.CellEditingTemplate>
Any ideas on whats wrong? The View's Viewmodel is connected in the code behind.
EDIT: The Binding that is not working is the ItemsSource binding shown above
When you use the DataTemplate of the DataGrid, you cannot use ElementName bindings as it won't resolve properly due to limitations in the resolution capabilities of FindControl within the DataGrid control hierarchy. You need to use a RelativeSource binding that travels up the control tree looking for a specific control type (which you need to determine - from your element name I assumed it was a DataGrid ancestor type).
<DataGridTemplateColumn.CellEditingTemplate>
<DataTemplate>
<ComboBox
SelectedItem="{Binding Operators}"
ItemsSource="{Binding DataContext.OperatorList,
RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}"
/>
</DataTemplate>
</DataGridTemplateColumn.CellEditingTemplate>
See this SO post that shares some potentially related sample code using MVVM to access the DataContext of the UserControl host to populate a ComboBox ItemsSource.
I am DataTemplating a listbox's ItemSource to display a series of comboboxes. I want to give the DisplayMemberPath of the combo to a property, which is in a different source than its own ItemsSource. (Assuming DisplayMemberPath is just a string representing name of a property, I am getting this from the user). I have achieved this with a CollectionViewSource, but all the comboboxes are displaying the same list.
What I am expecting to have after data templating is to have comboboxes display,
ComboboxInstance1.DisplayMemberPath = PropertyMapOfEmployee in FilterControls[0]
ComboboxInstance2.DisplayMemberPath = PropertyMapOfEmployee in FilterControls[1]
Is this possible to achieve in XAML ?
Thanks. Mani
UserControl:
<Resources>
<CollectionViewSource x:Key="bindingSource" Source="{Binding BindingItems}"/>
<CollectionViewSource x:Key="FilterSource" Source="{Binding FilterControls}"/>
<DataTemplate DataType="{x:Type CustomTypes:FilterElement}">
<ComboBox ItemsSource="{Binding Source={StaticResource bindingEmp}"
DisplayMemberPath="{Binding Source={StaticResource FilterSource},
Path=PropertyMapofEmployee}" />
</DataTemplate>
<Resources>
---
<DockPanel>
<ListBox x:Name="lstBox" ItemsSource="{Binding FilterControls}" />
</DockPanel>
ViewModel:
List<FilterElement> FilterControls;
List<Employee> Employees
class FilterElement
{
string Caption;
String PropertyMapofEmployee
}
<ComboBox ItemsSource="{Binding Source={StaticResource bindingEmp}"
DisplayMemberPath="{Binding PropertyMapofEmployee}" />
I'm not sure you can do that in XAML. (Having the DisplayMemberPath point to a property that is on an object other than the DataContext). You may want to look at the RelativeSource Class to see if that would meet your needs.
Have you thought about providing a reference in your Employee object to the FilterElement and then hooking up to the binding the Employee.PropertyMapOfEmployee property that you've created?
Why is the first element in my combobox popup menu not shown in the selected item area of
my combobox , when I use the SelectedItem binding? Without that it is showing up ?? Using
the same code selecteditem + selectedindex that is no problem!
<ComboBox
ItemsSource="{Binding SchoolclassSubjectViewModels}"
SelectedItem="{Binding SelectedSchoolclassSubjectViewModel}"
SelectedIndex="0"
Height="23"
HorizontalAlignment="Left"
Margin="375,13,0,0"
VerticalAlignment="Top"
Width="151">
<ComboBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding SchoolclassName}" />
<TextBlock Text=" " />
<TextBlock Text="{Binding SubjectName}" />
</StackPanel>
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
Well as workaround I used:
SchoolclassSubjectViewModels.Add(schoolclassSubjectVM);
SelectedSchoolclassSubjectViewModel = schoolclassSubjectVM;
and this:
SelectedItem="{Binding SelectedSchoolclassSubjectViewModel,Mode=TwoWay}"
but I would prefer the xaml only way as it should really work.
It is because the reference inside your ItemsSource collection is not the same as the one in your SelectedItem property. I would venture to guess that you are using one object context to query your database for the list of SchoolclassSubject objects which the ItemsSource is bound to, but another context to query the actual data item to which you bind the SelectedItem. Even though the list contains a reference which represents the value held by your object, it is not really the same reference, but a separate instance of the same data.
There are ways to solve this issue, most of them involve using the SelectedValuePath and SelectedValue instead of the SelectedItem properties, but the concrete solution would be different depending on your particular ORM.
I have a ListBox that contains a textbox and a combobox in its datatemplate:
<ListBox Height="147" Margin="158,29,170,0" Name="PitcherListBox" VerticalAlignment="Top" ItemsSource="{Binding SomeCollectionOfObjects}" Background="Black">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBox Text="{Binding Path=Name}" />
<ComboBox ItemsSource="{Binding LocalArrayOfIntsProperty}" />
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
I want to bind the listbox to a collection of objects (which I've done successfully), but I want the combobox in the above datatemplate to have its itemssource set to a local property on the window (array of ints). I still want the combobox to have a two-way bind between its selected item and a property on the collection of objects...
I have the following in code:
PitcherListBox.DataContext = this;
Basically in the end, I want the combobox within the listbox to have a different itemssource than the listbox itself. I can't seem to figure out how to change the ComboBox's ItemsSource in XAML. Can someone provide me some feedback? Thanks!
Try this:
<ComboBox ItemsSource="{Binding LocalArrayOfIntsProperty, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type YourWindowTypeHere}}}" />
Note that you need to replace YourWindowTypeHere with the type of the Window containing the LocalArrayOfIntsProperty! Also remember that you will need to define an xml namespace for that type!
I'm displaying all of my customers which I get from a ViewModel ObservableCollectoin property within a ComboBox like this:
<ComboBox
ItemsSource="{Binding Customers}"
ItemTemplate="{StaticResource CustomerComboBoxTemplate}"
Margin="20"
HorizontalAlignment="Left"
SelectedItem="{Binding SelectedCustomer, Mode=TwoWay}"/>
Is there a way to get the number of items in the ObservableCollection without creating another ViewModel property, e.g. something like this:
PSEUDO-CODE:
<TextBlock Text="{Binding Customers.Count()}"/>
The ObservableCollection type exposes a Count Property which you can use.
I don't know if ObservableCollection raises the PropertyChanged event in order to inform the UI about updates to this property though.