I'm sure it's something stupid, but I'm playing around with databinding. I have a checkbox and a label on a form. What I'm trying to do is simply bind the Content of the label to the checkbox's IsChecked value.
What I've done runs fine (no compilation errors and acts as expected), but if I touch the label in the XAML, the designer trows an exception:
System.NullReferenceException
Object reference not set to an instance of an object.
at MS.Internal.Designer.PropertyEditing.Editors.MarkupExtensionInlineEditorControl.BuildBindingString(Boolean modeSupported, PropertyEntry propertyEntry)
at
<Window x:Class="UnitTestHelper.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:FileSysCtls="clr-namespace:WPFFileSystemUserControls;assembly=WPFFileSystemUserControls"
xmlns:HelperClasses="clr-namespace:UnitTestHelper"
Title="MainWindow" Height="406" Width="531">
<Window.Resources>
<HelperClasses:ThreestateToBinary x:Key="CheckConverter" />
</Window.Resources>
<Grid Height="367" Width="509">
<CheckBox Content="Step into subfolders" Height="16" HorizontalAlignment="Left" Margin="17,254,0,0" Name="chkSubfolders" VerticalAlignment="Top" Width="130" IsThreeState="False" />
<Label Height="28" HorizontalAlignment="Left" Margin="376,254,0,0" Name="lblStepResult" VerticalAlignment="Top" Width="120" IsEnabled="True" Content="{Binding IsChecked, ElementName=chkSubfolders, Mode=OneWay, UpdateSourceTrigger=PropertyChanged, Converter={StaticResource CheckConverter}}" />
</Grid>
The ThreeStateToBinary class is as follows:
class ThreestateToBinary : IValueConverter
{
#region IValueConverter Members
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if ((bool)value)
return "Checked";
else
return "Not checked";
//throw new NotImplementedException();
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return ((string)value == "Checked");
//throw new NotImplementedException();
}
#endregion
}
Quite honestly, I'm playing around with it at this point. It was originally simpler (not using the ValueConverter) but was displaying similar behavior when I simply had the content set to:
Content="{Binding IsChecked, ElementName=chkSubfolders, UpdateSourceTrigger=PropertyChanged}"
Any ideas?
Thanks,
John
Try removing UpdateSourceTrigger=PropertyChanged. In this case, the checkbox is your source and the label is your target. The label doesn't change, and furthermore, you set the mode to OneWay which binds only from the source to the target. Therefore, it's meaningless to tell it the binding to update the source on property changed. It might not be causing your problem, but it seems suspect (or at least weird).
Related
I have an custom control with following DP:
public FrameworkElement NoResultContent
{
get { return (FrameworkElement)GetValue(NoResultContentProperty); }
set { SetValue(NoResultContentProperty, value); }
}
public static readonly DependencyProperty NoResultContentProperty =
DependencyProperty.Register("NoResultContent", typeof(FrameworkElement), typeof(AdvancedAutoCompleteBox), new PropertyMetadata(null));
The ControlTemplate of my custom control shows this DP in a ContentControl:
<ContentControl Content="{TemplateBinding NoResultContent}" />
It's used in a view to provide arbitrary functions:
<Controls:AdvancedAutoCompleteBox
x:Name="Box"
ItemsSource="{Binding Persons}"
SelectedItem="{Binding SelectedPerson}"
Watermark="Search here">
<Controls:AdvancedAutoCompleteBox.NoResultContent>
<StackPanel>
<Button
Content="Add by ICommand"
Command="{Binding AddPerson}" />
<Button
x:Name="AddPerson"
Content="Add by Caliburn" />
</StackPanel>
</Controls:AdvancedAutoCompleteBox.NoResultContent>
</Controls:AdvancedAutoCompleteBox>
The Command-Binding to a ICommand works just fine. Buy why does it not work with Caliburn.Micro?
I also tried to attach the context to the second Button manually by cal:Bind.Model
I'm trying to bind my ListBox to a selection of my ViewModel, because I have multiple ListBoxes in a Pivot and I don't want to type out the entire Page for each property. To illustrate my issue, here's a small sample:
XAML:
<DataTemplate x:Key="PropertyTemplate">
<StackPanel>
<TextBlock Text="{Binding Label}" />
<TextBlock Text="{Binding Value}" />
</StackPanel>
</DataTemplate>
<controls:Pivot>
<controls:PivotItem>
<ListBox ItemsSource="{Binding PropertySelectionOne}" ItemTemplate="{StaticResource PropertyTemplate}" />
</controls:PivotItem>
<controls:PivotItem>
<ListBox ItemsSource="{Binding PropertySelectionTwo}" ItemTemplate="{StaticResource PropertyTemplate}" />
</controls:PivotItem>
</controls:Pivot>
ViewModel:
public class SomeViewModel
{
private Property _propOne;
public Property PropOne
{
get { return _propOne; }
set { _propOne = value; NotifyPropertyChanged("PropOne"); }
}
private Property _propTwo;
public Property PropTwo
{
get { return _propTwo; }
set { _propTwo = value; NotifyPropertyChanged("PropTwo"); }
}
private Property _propThree;
public Property PropThree
{
get { return _propThree; }
set { _propThree = value; NotifyPropertyChanged("PropThree"); }
}
}
So basically I want to bind my ListBoxes to PropertySelectionOne and PropertySelectionTwo, which would contain references to a selection of the properties in my ViewModel. For instance, PropertySelectionOne could include PropOne and PropTwo and PropertySelectionTwo could include PropTwo and PropThree.
Is there a simple way to "group" these properties to a new property to bind against without changing the architecture of my application?
Thanks
If you've got different properties to be displayed from the same date type in different list boxes, then arguably you need to split your view model, but you say you don't want to change the architecture of your application, which is your choice.
So, what you need to do is to provide a different ItemTemplate for each ListBox that defines which properties and how you want to display in each ListBox. Then you can bind the ItemsSource for all of the list boxes to the same data source but they will present different properties according to the ItemTemplate.
Not sure how familiar you are with these concepts, but you know that ItemsSource needs to be a collection of your data instances (SomeViewModel?), right?
I currently have a ResourceDictionary file for my WPF application, which pretty much adds every style that I could possibly want throughout all of my application's DataGrids.
Except one.
How can I add a global "IsReadOnly" setter, for all of my DataGrid's DataGridTextColumn columns ?
Basically, I use a few DataGrids, and if I want to display read-only data in a particular column, I'll just display the data using a DataGridTextColumn:
<WPFtoolkit:DataGridTextColumn Binding="{Binding Path=DOB,StringFormat='dd/MMM/yyyy'}" Header="DOB" Width="120" />
However, if I have a column which has editable data, then I'll use a DataGridTemplateColumn instead.
<WPFtoolkit:DataGridTemplateColumn xHeader="Department Name" >
<WPFtoolkit:DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<ComboBox Width="175"
ItemsSource="{Binding Source={StaticResource AllDepartmentsDataSource}}"
SelectedValue="{Binding DepartmentID}" SelectedValuePath="DepartmentID" DisplayMemberPath="DepartmentName"
VerticalAlignment="Center"
>
</ComboBox>
</DataTemplate>
</WPFtoolkit::DataGridTemplateColumn.CellTemplate>
</tWPFtoolkit:DataGridTemplateColumn>
The problem is, for every one of my DataGridTextColumns, I specifically need to add the IsReadOnly parameter, otherwise the user can (incorrectly) edit that data:
<WPFtoolkit:DataGridTextColumn IsReadOnly="True" Binding="{Binding Path=DOB,StringFormat='dd/MMM/yyyy'}" Header="DOB" Width="120" />
Is there a way to add this "IsReadOnly" setting globally, in the ResourceDictionary file, to all of my DataGridTextColumns...?
I can add global styles to DataGrid, DataGridColumnHeader, DataGridRow, and DataGridCell, but if I try to define a style with a TargetType of DataGridTextColumn, then Visual Studio complains that DataGridTextColumn is not derived from a FrameworkElement or FrameworkContentElement.
<Style TargetType="{x:Type WPFToolkit:DataGridTextColumn}">
<Setter Property="IsReadOnly" Value="True"/>
</Style>
I can add IsReadOnly to the Grid style, but this makes all columns uneditable !
Can anyone think of an quick and easy way to add this simple property to the DataGridTextColumns ?
Update:
My solution has been (reluctantly) to add a Loaded handler to each of my DataGrids, which runs this code:
void grdGrid_Loaded(object sender, RoutedEventArgs e)
{
DataGrid dg = (DataGrid)sender;
foreach (DataGridColumn col in dg.Columns)
{
DataGridTextColumn textCol = col as DataGridTextColumn;
if (textCol != null)
{
textCol.IsReadOnly = true;
}
else
{
// This DataGridColumn isn't of type "DataGridTextColumn", so do nothing.
}
}
}
You could, of course, put this in your own DataGrid-inherited control, rather than repeating it for each of your DataGrids.
(Sigh.)
Why didn't MS make IsReadOnly an attachable property..? It would've made life so much easier!
I'm a bit of a .net newbie and I've been working on my first big silverlight project. So pardon the lack of lingo and the length of the question. But my problem is as follows.
The project is being built according to the MVVM pattern ( in this case I'm using LightMVVM ). Most of the views contain ListBoxes. These listboxes need to handle multiple different types of data each of which has it's own visual look. After some poking around I decoded tp try this implementation for datatemplate selection:
http://silverscratch.blogspot.com/2010/04/changing-data-templates-at-run-time.html
Some of my items, however, have sub controls that need to talk to the viewmodel. From what I've been reading Commands with element bindings is the best ways to handle this.
So, for example:
<Grid x:Name="NavMainLayoutRoot" DataContext="{Binding Source={StaticResource NavMainViewModelDataSource}}" Margin="15,0,0,0">
....
<ListBox x:Name="MenuListBox" HorizontalAlignment="Left" Background="{x:Null}" BorderBrush="{x:Null}" Foreground="White" ItemsSource="{Binding Items}" ItemContainerStyle="{StaticResource MainNavigationButtonStyle}" Padding="0" VerticalAlignment="Top" >
<ListBox.RenderTransform>
<CompositeTransform/>
</ListBox.RenderTransform>
<ListBox.ItemTemplate>
<DataTemplate>
<xxxControls:SelectableContentControl TemplateName="{Binding Path=Type}" Content="{Binding Details}" IsTabStop="{Binding IsHitTestEnabled}">
<xxxControls:SelectableContentControl.Templates>
<DataTemplate>
<local:GenericItem />
</DataTemplate>
<DataTemplate x:Name="navbutton">
<local:MainNavItem />
</DataTemplate>
</xxxControls:SelectableContentControl.Templates>
</xxxControls:SelectableContentControl>
</DataTemplate>
</ListBox.ItemTemplate>
....
And MainNavItem, simplified is:
<Grid x:Name="NavItemRoot" VerticalAlignment="Top" Margin="0,0,0,0">
<Button Content="{Binding Label}" VerticalAlignment="Top" Style="{StaticResource MainNavItemButtonStyle}" HorizontalAlignment="Left" Margin="5,0" Command="{Binding DataContext.NavButtonClick, ElementName=NavMainLayoutRoot}"/>
</Grid>
The problem is that this didn't work. So for grins I went ahead and copy and pasted the code for the MainNavItem directly into the tag and like magic it started working.
Since I reuse a lot of these item templates all over the application, having them in nice contained external files is very nice and not something I want to give up.
(( Thinking about it, this example is not the best, suffice it to say that some of these data templates contain multiple controls and I can't just use selectedItem on the listbox to handle the selected events. ))
So any suggestions are welcome. What's the best practice here?
My first thought is that something in your MainNavItem user control is setting its DataContext to something else. If you don't set the DataContext it should automatically pick it up from the current item in your MenuListBox.
You can try creating a test value converter and putting a breakpoint in it to check what the data context is at runtime.
public class TestConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
Debug.WriteLine("TestConverter.Convert(value := {0}, targetType := {1}, parameter := {2}, culture := {3})",
value, targetType, parameter, culture);
return value; // put break point here to test data binding
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
Debug.WriteLine("TestConverter.ConvertBack(value := {0}, targetType := {1}, parameter := {2}, culture := {3})",
value, targetType, parameter, culture);
return value;
}
}
And modify your MainNavItem to look like this in order to break in the TestConverter at runtime.
<UserControl.Resources>
<ResourceDictionary>
<TestConverter x:Key="TestConverter" />
</ResourceDictionary>
</UserControl.Resources>
<Grid x:Name="NavItemRoot" DataContext="{Binding Converter={StaticResource TestConverter}}">
<Button Content="{Binding Path=Label, Converter={StaticResource TestConverter}}" />
</Grid>
This will help you determine the issue with data binding.
I suspect that the problem with your command is that you're using element-to-element data binding to attempt to bind to an element that is outside of the user control you're currently within. This won't work. Instead, try setting up your NavMainViewModelDataSource static resource in App.xaml, then you can bind directly to it from your user control.
<Button Content="{Binding Label}" Command="{Binding Path=NavButtonClick, Source={StaticResource NavMainViewModelDataSource}}" />
I have a hierarchy of view models representing formatted content:
public abstract class ContentPartViewModel : ViewModel
{
}
public class TextContentPartViewModel : ContentPartViewModel
{
public string Text { ... }
}
public class TitleContentPartViewModel : TextContentPartViewModel
{
}
public class HyperlinkContentPartViewModel : TextContentPartViewModel
{
public string Uri { ... }
}
I have an encompassing view model that contains a collection of ContentPartViewModels to be rendered:
public class ContentViewModel
{
public ICollection<ContentPartViewModel> ContentParts { ... }
}
I then have a ContentView that renders all parts of the content:
<UserControl ...>
<ItemsControl ItemsSource="{Binding ContentParts}"/>
</UserControl>
In an ideal world, I would just define a DataTemplate for each of the content part types and they would be rendered accordingly. However, Silverlight does not support the DataType property on the DataTemplate class, so that is not an option.
Another option would be to provide a DataTemplateSelector and do the mapping from view model type to DataTemplate myself. Alas, ItemsControl in SL2 does not have an ItemTemplateSelector property - only an ItemTemplate property.
That left me with no option but to provide an ItemTemplate that then uses a converter to turn off all the UI apart from the piece relevant to that content part:
<ItemsControl.ItemTemplate>
<DataTemplate>
<Grid>
<TextBlock Text="{Binding Text}" FontWeight="Bold" Visibility="{Binding Converter={StaticResource TitleContentPartConverter}}"/>
<TextBlock Text="{Binding Text}" Visibility="{Binding Converter={StaticResource TextContentPartConverter}}"/>
<HyperlinkButton Content="{Binding Text}" NavigateUri="{Binding Uri}" Visibility="{Binding Converter={StaticResource HyperlinkContentPartConverter}}"/>
</Grid>
</DataTemplate>
</ItemsControl.ItemTemplate>
This is obviously rather awful, both for performance and for readability/correctness of code. It also makes it much harder for me to format the output correctly. So, questions:
Can anyone recommend a better way to do this in SL2?
Can anyone confirm whether the situation has improved in SL3?
Thanks,
Kent
Yes. DataType in DataTemplate is not supported in Silverlight 2 or Silverlight 3.
You can work around ItemTemplateSelector in Silverlight. Please take a look at this sample.
http://silverlight.net/forums/t/12598.aspx
protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
{
base.PrepareContainerForItemOverride(element, item);
DataTemplateSelector selector = this.ItemTemplateSelector;
if (null != selector)
{
((ContentPresenter)element).ContentTemplate = selector.SelectTemplate(item, element);
}
}