I have a window control in which I am loading a wpf user control. The wpf user control contains a combo box which is bound to a property in the view model. When I am debugging the code selected value property always has a value. When the control is loaded for the first time I am getting the selected value, but when I reload the control the combo box gets cleared. I tried everything; updating the source and other stuff, but it's still not working. I even set the datacontext in code behind, but am still not getting the expected output.
This is the XAML code:
<ComboBox x:Name="cmbType" Style="{StaticResource ComboBoxStyle}"
PreviewTextInput="cmbErrorType_PreviewTextInput" IsEditable="True"
MaxDropDownHeight="100" ItemsSource="{Binding Path=TypeList,Mode=OneWay}"
SelectedValue="{Binding Path=SelectedValue}" DisplayMemberPath="Id"
SelectedValuePath="Id" Grid.Row="0" Grid.Column="1" Grid.ColumnSpan="2"/>
Related
I have a combobox which displays listview on dropdown, I am following MVVM Pattern and i have also set the public property in my Viewmodel and it works fine when i am assigning it to the Label but for Combobox it doesn't seem to rely on my binding. i tried numerous ways but unable to find the issue.
XAML :
<ComboBox Name="SearchBox" IsEditable="True" Background="White" md:HintAssist.Hint="Search MUID" Grid.Column="1" Margin="5 0 0 0"
Grid.Row="0" Height="40" Width="400" HorizontalContentAlignment="Left" HorizontalAlignment="Left" SelectedItem="{Binding ElementName=lstview ,Path=SelectedItem}" >
<ComboBoxItem>
<ListView x:Name="lstview" ItemsSource="{Binding filterSW}"
SelectedItem="{Binding SelectedMU}"
Height="200" ScrollViewer.VerticalScrollBarVisibility="Visible">
<ListView.View>
<GridView>
<GridViewColumn Width="130" Header="Mu-ID" />
<GridViewColumn Width="130" Header="MU-Identifier" DisplayMemberBinding="{Binding MU_Identifier}" />
<GridViewColumn Width="130" Header="Status" DisplayMemberBinding="{Binding RequestType}" />
<GridViewColumn Width="130" Header="UniqueID" />
</GridView>
</ListView.View>
</ListView>
</ComboBoxItem>
</ComboBox>
This works fine for me when i am using the public property and accessing its element , i also tried setting text={Binding SelectedMU.MU_Identifier} and selectedvalue but its just not working.
<Label Grid.Column="3" HorizontalAlignment="Center" Background="GreenYellow" Content="{Binding SelectedMU.MU_Identifier}"></Label>
It looks like you're trying to show a multi-column list in your ComboBox dropdown instead of the standard list where each item shows just a text line.
To achieve this effect you've placed a ListView inside the dropdown.
Unfortunately, this is just not going to work.
Both ComboBox and ListView descend from Selector which is an abstraction that allows to select an item from a list. This limits the property SelectedItem to one of the items that are contained in the list. If you try to assign to this property any value that it not in the list, the assignment is not going to work and the property will retain the value it had before you did the assignment.
Now, the list could either be specified right inside XAML or provided as a binding to property ItemsSource. You do the binding correctly for the ListView. But for the ComboBox you don't specify that binding. Instead you specify exactly one item of type ComboBoxItem which contains the whole ListBox as its value. So the only value that could be successfully assigned to the SelectedItem property of the ComboBox is that single ComboBoxItem. But your binding is never going to assign that value, that's why the ComboBox never shows anything when closed.
When it's open it does show the single item which contain the ListView but this is just an optical effect. The data binging is not going to work. The reason why it works for the Label is because the Label is not constrained and can show anything that the ListView tells it to show.
You can synchronize the ListView and the ComboBox only when both controls have the same bindings for both ItemsSource and SelectedItem properties. But in this case you won't be able to place the ListView inside the dropdown.
The closest you can get to what you want is by customizing the ComboBox's template as described in https://zamjad.wordpress.com/2012/08/15/multi-columns-combo-box, for example. What this won't give you compared to ListView is the column headers. Also, the columns will be evenly spaced inside the dropdown but this is what you have in your ListView anyway.
If you want to auto-size them, you'd need to add Width="Auto" SharedSizeGroup="cN" to each ColumnDefinition where "cN" should have the column number instead of N to make them unique within the Grid and add Grid.IsSharedSizeScope="True" to the <ComboBox >
That's a lot of trouble for something that one would expect to be much simpler, but, unfortunately, you cannot place a ListView inside the ComboBox's template, that's a limitation of how the base class Selector works with its items list.
There are other options if you are open to consider 3rd party control libraries. I worked with Syncfusion, they have SfMultiColumnDropDown which does what you want. I'm pretty sure other popular libraries have similar controls as well.
I have a ComboBox bound to an ObservableCollection<IDrive>
The problem is that IDrive does not support INotifyPropertyChange nor should it.
While the number of elements in my ComboBox is fixed and does not change, the labels shown in the ComboBox can and will change.
How do I get these labels to update?
Firing PropertyChanged on my ObservableCollection does not refresh the content of the labels but it does reset the SelectedItem which is a side-effect I don't even want.
Here's my current XAML:
<ComboBox Grid.Column="1" Grid.Row="0" Grid.ColumnSpan="4"
ItemsSource="{Binding Drives}" SelectedItem="{Binding SelectedDrive}"
IsSynchronizedWithCurrentItem="True" DisplayMemberPath="Label"
Margin="5,5,5,5" VerticalAlignment="Center" />
Label being the property in my IDrive interface
You will need to wrap the items in a DriveViewModel : INotifyPropertyChanged and have that repeat the relevant properties. And somehow trigger the changed event from that.
On second thought, I'm not sure if DisplayMemberPath picks up on this. You'll probably need an ItemTemplate as well.
I have a thread that updates the current Mode property every second. I also want an option to be able to set a mode within the same cell in datagrid. So, in not editing mode I just show the mode. In editing mode, I show a populated ComboBox.
Now,
to be able to show the selected item in ComboBox, when I enter the editing mode, I bind the SelectedItem to Mode.
to be able to get the changes back to the ViewModel I bind SelectedValue to a different property. ( I need to bind to a different property since 'Mode' is updated every second and will overwrite the selected value).
The problem is that though SelectedItem is bound with Mode=OneTime it still triggers SelectedValue property. I want the SelectedValue to be triggered only when user select a value.
I hope it's clear what I'm trying to do. So, how I can achieve this? Other approaches are welcome (even if I need to use a different control).
<DataGridTemplateColumn Header="Mode">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBlock Text="{Binding Mode}"/>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
<DataGridTemplateColumn.CellEditingTemplate>
<DataTemplate>
<ComboBox ItemsSource="{Binding Source={StaticResource Modes}}"
SelectedItem="{Binding Mode, Mode=OneTime}"
SelectedValue="{Binding ModeToSet, Mode=OneWayToSource}"
/>
</DataTemplate>
</DataGridTemplateColumn.CellEditingTemplate>
</DataGridTemplateColumn>
The premise of what needs to be done is not attainable due to the way the combobox works and how Mode is constantly changing in the background.
Why?
The problem is that though SelectedItem is bound with Mode=OneTime it
still triggers SelectedValue property.
As it should. OneTime as per the docs (BindingMode Enumeration) states:
"Updates the binding target when the application starts or when the data context changes."
The data context as per your design is always changing once a second. If one reads farther into the description it states
"This type of binding is appropriate if you are using data where either a snapshot of the current state is appropriate to use or the data is truly static. ... This is essentially a simpler form of OneWay binding..."
And if one reads up on OneWay bindings
"Updates the binding target (target) property when the binding source (source) changes. This type of binding is appropriate if the control being bound is implicitly read-only."
A combo box is ultimately designed to change both SelectedItem and to get the value off of SelectedItem into SelectedValue
I want the SelectedValue to be triggered only when user select a value.
The problem is not going out of the control, it is what is coming in....
Create a test project and the combobox behaves the way you specify, selected value is only triggered when a user selects a value. Comboboxes only sets the SelectedX properties when a choice is made or an outside value has changed one so it changes the other.
Since Mode is constantly changing it is pushing the change into the selection, not visa versa.
Suggestion To Fix
I suggest you take a snapshot of mode and place that into a ModeOnEdit variable and bind that. When the user makes the selection, capture the event and change the actual Mode.
Test Project
Bind to your own data source, mine was Ships. Ships is a list with and Name as a property on that object. ToString on the ship object returns Name.
Here is the result, there are two textboxes which show the state of the selected item/value. A button to set the selected value and the combobox itself.
<Label Grid.Row="1" Grid.Column="1">SelectedItem</Label>
<TextBlock Grid.Row="1" Grid.Column="2" Text="{Binding SelectedItem, ElementName=cbMain}"/>
<Label Grid.Row="3" Grid.Column="1" Grid.ColumnSpan="2">SelectedValue</Label>
<TextBlock Grid.Row="3" Grid.Column="2" Text="{Binding SelectedValue, ElementName=cbMain}"/>
<Button Grid.Row="5" Grid.Column="1" Click="ChangeSelectedValue">Set Selected Value</Button>
<ComboBox Name="cbMain"
Grid.Row="5"
Grid.Column="2"
ItemsSource="{Binding Ships}"
SelectedValuePath="Name"/>
-- Code behind
private void ChangeSelectedValue(object sender, RoutedEventArgs e)
{
cbMain.SelectedValue = "Pacific Silver";
}
I have a textblock that when the user is selected from a drop down the following TextBlock displays the "Name" of the user. This works great!
<TextBlock Text="{Binding Name, Mode=OneWay}"/>
However, on another part of the screen I a TextBox:
<TextBox x:Name="newName" Text="{Binding Name}">
Which is editable and contains the same data.
So right now when a User is selected both elements gets populated but I want to prevent the TextBlock from being updated when the TextBox is updated.
You could use "OneTime" binding mode on the textblock to get a snapshot of the data on init or context change.
-m
I am working with the the WPF Toolkit DataGrid and currently have a problem with committing data back to the source.
My grid is bound to a CLR object list and I have a converter with both the convert and convert back methods implemented.
The two way binding works fine if the user hits Enter in the cells but if they deselect or tab out of the cells the data that was typed is lost.
I have put a break on the CellEditEnding event and both events for Tab and Enter seem identical, but when it gets to the ConvertBack method on my converter the value is empty.
Any help would be much appreciated.
Try changing the UpdateSourceTrigger parameter of your control's Binding to PropertyChanged instead of the default LostFocus.
Eg
<TextBox
Width="75"
VerticalAlignment="Top"
Margin="10"
Text="{Binding
Source={StaticResource data},
Path=Age,
UpdateSourceTrigger=PropertyChanged,
ValidatesOnDataErrors=True,
ValidatesOnExceptions=True}"
Style="{StaticResource textBoxInError}" />