This is a bit of a WPF whodunnit! My validation temples it not appearing when expected
The Problem
Basically, I am using IDataErrorInfo on my view model to provide feedback on data entry errors. I can see this being called and working as expected, but the validation error template for the bound control is never displayed by WPF!
I have tried both using the built-in default textbox red border error template, a style error template, and a hard coded template. None of these are displayed in a data error situation.
Heres my xaml binding code:
<TextBox x:Name="txtCaseNumber"
Text="{Binding Path=CaseNumber, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}"/>
Wierdly, the error gets into the Validation.Errors collection. The follow code results in my IDataErrorInfo error message getting displayed next to the bound control. This leads me to think the problem is on the xaml side, rather the viewmodel side.
<ContentPresenter
Content="{Binding ElementName=txtCaseNumber, Path=(Validation.Errors).CurrentItem}" />
Additionally,
System.Windows.Controls.Validation.GetHasError(txtCaseNumber) returns true.
I am hosting WPF in winforms if that makes a difference. I can't find any references in my code or styles to Validation or ErrorTemplate so I'm pretty sure this isn't a styling own goal.
Cracked it.
The ErrorTemplate attached property uses the adorner layer to show error templates on data validation failures reported via IDataErrorInfo. The Adorner layer is not always available for all controls in all situations. Your control or one of its parents needs to explicitly provide one.
The default Window control template contains an AdornerDecorator which enables the adorner layer for its children. This why my other window showed my error templates just fine, because this window used the default control template
The window which didn't show my error template had used a style which provided a ControlTemplate for my window. This control template did not provide an <AdornerDecorator>, hence no adorner layer to show my error template.
The fix was as simple as wrapping my window control template with <AdornerDecorator>.
Related
I am reasonably proficient in XAML and WPF having trouble with binding to an additional control within an extended control from outside the control. Sorry, that's a real mouthful so let me explain:
I have a control that I have extended from a ComboBox and applied the template and overridden the property metadata and all that stuff and re-templated it so it looks and works as I want it to. Now, I want to add a TextBox to provide search functionality for the ComboBox which I have exposed dependency properties to determine if it is visible or not and added this to the first row of the Grid above the ItemsControl and all works fine. I have added a dependency property called IsFiltered and applied a template binding to determine if the filter is visible and from outside my control I can set this value and it all works.
However, I have added a dependency property to the extended ComboBox (MyComboBox if you like) as a string property so that I can assign a filter text property from my view model that will eventually work its way to the text box embedded within the control. The TextBox in the conrol is also bound using {TemplateBinding FilterText} dependency property, as it hooks back to my MyConboBox control and the assignment is accepted and recognised. However, while the property from my view model is set and read and interacts with the FilteText property in MyComboBox to which the TextBox inside by MyComboBox control template is also bound to, the TextBox does not trigger a change.
<TextBox
Grid.Row="0"
Margin="4"
Text="{TemplateBinding FilterText}"
BorderBrush="Red"
Visibility="{TemplateBinding IsFiltered, Converter={converters:BoolToVisibilityConverter}}"/>
Can anyone help?
Similar to creating a data binding in Windows Forms designer, I am creating a databound item on my blank WPF control by dragging and dropping the property of my custom simple object onto it from the Data Sources window. It creates the expected label with the data field name and text box control, and compiles fine. But when I run the application it throws the following error:
{"Unable to cast object of type 'System.Windows.Controls.Grid' to type 'System.Windows.Data.CollectionViewSource'."}
How do I fix it?
The markup generated by the designer doesn't work. The Grid that's nested around the label and text box has a DataContext property of the form {StaticResource mySimpleObjectViewSource}, but needs to be of the form {Binding Source={StaticResource mySimpleObjectViewSource}}.
I have a rather interesting case with ComboBox control - CustomComboBox;
In the style of this ComboBox, Popup contains one custom control that requests a DataContext;
<ctrl:CustomGrid DataContext="{TemplateBinding DataContext}" GridName="{Binding Preferences.CurrentGridName}"/>
The idea:
to use this control several times on one page
to use it in a masterpage container
the masterpage control needs to have different DataContexts regarding the Page it is on
The logic:
In the overriden OnApplyTemplate I am getting the grid and connecting few eventhandlers
The problem:
The masterpage control is triggering OnApplyTemplate only once
The first appearance of the CustomComboBox is as expected.
However, every next apearance is with same DataContext, even when changing the datacontext of the CustomComboBox
These changes don't reach to change my CustomGrid DataContext
I am sure that something on the bindings or the presentation logic is bad...
Please throw some thoughts on, I would appreciate a hint here
Thanks
OnApplyTemplate is called when a ControlTemplate is applied to the control that overrides the method (neither its parent, nor children). If OnApplyTemplate is entered once, the overriding control must also be created once. I mean you simply have a single masterpage instance. This shouldn't be unexpected.
Speaking about Popups and DataContext, there often are issues with bindings from a Popup to outside it. So, I would rather write some code-behind to deliver correct context to Popups, instead of relying on Bindings. There sure is a problem of DataContextChanged event absence prior to SL5. To workaround this one, you should define your custom DependencyProperty on your CustomComboBox, bind it to the CustomComboBox's context and assign its value to the Popup in the PropertyChangedCallback.
I have a user control that has a textbox in it, and i am using a clear button on my main form to clear information from the entire main window. i would like to clear the textbox in the user control once the clear button is clicked as well. i havent found an easy way to do this. i have tried referencing the control's name in c# followed by a "." however the name of the text box does not show up. any help would be appreciated!
WPF declares controls in a UserControl as private. To make your TextBox public you declare it with a FieldModifier as in:
<TextBox x:FieldModifier="Public" />
where x is the xaml namespace xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml". However the recommended way of clearing a TextBox is to bind it to a property and then clear the property.
You should not try to directly access controls within a UserControl from external classes or code. The simple mechanism would be to add a Clear() method to the UserControl which clears all relevant controls and information inside the UserControl.
The textbox could be bound to the DataContext of the UserControl. So a way of clearing it might be setting the property that is bound to the Text property of the TextBox to an empty string.
I have a few usercontrols loaded into a tabcontrol via MVVM in WPF.
Within the XAML for the usercontrol I am setting focus to a textbox using the FocusManager, however this appears to only work when the first instance of the usercontrol is created.
Just to test I added a loaded event handler to the usercontrol - this is only called on the first instance.
I'm using data templates for the user controls as follows:
<DataTemplate DataType="{x:Type local:UserTypeViewModel}">
<local:UserTypeView />
</DataTemplate>
The textbox is focused as follows:
FocusManager.FocusedElement="{Binding ElementName=txtName}"
Additionally I'm using a global event handler (for the textbox GotFocus event) which selects all the text using a dispatcher.
If anyone has any tips on how to achieve focus with every usercontrol I'd be very grateful.
Thanks, Ben.
Remember that a visual element can only receive focus, if:
It is visible (in a TabControl only one tabitem can be visible at a time
IsFocusable must be set to true (is default false for UserControls)
It has finished loading (as you write - do it in the Loaded event))
I think the first reason is why it only works for the first element.
As for how to achieve it for all controls - you can use a style with an EventSetter for the Loaded event. You need to make a style per type of control though to avoid having to set it for each control.