We Keep Coding

Validation MarkInvalid Textbox using MVVM

I have a textbox that has validation on it, in the validation checks to see if its isNullOrEmpty. The validation works but what I am having difficulty is if the user never selects the textbox and clicks save, I want the validation to run again.
I was able to accomplish this in the XAML.cs file using:
Validation.MarkInvalid(cb.GetBindingExpression(dp), validationError);
Now with MVVM I'm confused how I am able to accomplish this from the viewmodel.
Textbox in question:
<TextBox>
<TextBox.Text>
<Binding Path="LastName">
<Binding.ValidationRules>
<validationRules:IsNullOrEmptyValidationRule/>
</Binding.ValidationRules>
<Binding.UpdateSourceTrigger>PropertyChanged</Binding.UpdateSourceTrigger>
<Binding.Mode>TwoWay</Binding.Mode>
</Binding>
</TextBox.Text>
</TextBox>
Any ideas?

WPF Validation not firing when first load

In Prism application I want to using validation.And I have implement the INotifyDataError interface in my ViewModel ,but I found that the validate solution don't be fired when the control is loaded first time.
Then I found the same Question like 'wpf Validation Binding not fired on First Load'
I Found a solution to solve the problem WPF don't fired the validation when first load the datacontext is that:
<TextBox Grid.ColumnSpan="2" Grid.Row="1" x:Name="textBoxFolder" Margin="2,4">
<TextBox.Text>
<Binding Path="this.MovieFolder" UpdateSourceTrigger="PropertyChanged">
<Binding.ValidationRules>
<!-- Validation rule set to run when binding target is updated. -->
<Rules:MandatoryInputRule ValidatesOnTargetUpdated="True" />
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
as you see,ValidatesOnTargetUpdated="True" is the key point ,this property will make WPF fired the validation when the datacontext load first time.
But I think that's a ugly solution. I need to add a Binding.ValidationRules for every control I want to validate.
Is there a good way to solve the problem.

OK I've solved it: You force the validation when the element got bound with a simple property - ValidatesOnTargetUpdated:
<rules:MyValidationRule ValidatesOnTargetUpdated="True" ValidationType="notnull"/>

WPF Button IsEnabled Check on Multiple Bindings

I have the IsEnabled property of a XAML button configured with the following databinding currently:
<Button Name="ThirdPartyPostoneButton" Content="Postpone"
Click ="postponeThirdPartyUpdatesButton_Click" Margin="5,5,0,0"
Height="25" IsEnabled="{Binding Item3.CanDefer}"/>
I need to also add a check for IsEnabled="{Binding Item3.InstallSourceExists}" (in other words both criteria must be met in order for the button to be enabled). How can I accomplish this?

Two options I can think of:-
Use a MultiBinding plus a custom IMultiValueConverter that checks both values are true.
Expose a new property on your "Item3" model that simply returns true if the other properties are both True. This is a cleaner approach, and means that if the logic changes in the future (e.g. you need to include a third bool property), you don't have to touch your XAML.

Use a multibinding like this:
<Button Name="ThirdPartyPostoneButton" Content="Postpone" Click ="postponeThirdPartyUpdatesButton_Click" Margin="5,5,0,0" Height="25" >
<Button.IsEnabled>
<MultiBinding Converter="{StaticResource MyCustomConvertor}">
<Binding Path="Item3.CanDefer"/>
<Binding Path="Item3.InstallSourceExists"/>
</MultiBinding>
</Button.IsEnabled>
</Button>

DependencyProperty Binding with ValidationRule not updating Source when ValidationResult is false

A ComboBox.SelectedItemProperty is bound TowWay to a DependencyProperty in
The Control.
In the ControlTemplate :
<ComboBox IsEditable="True">
<ComboBox.SelectedItem>
<Binding RelativeSource="{RelativeSource TemplatedParent}"
Path="SomeDP" Mode="TwoWay" NotifyOnValidationError="True">
<Binding.ValidationRules>
<vld:DeleteAfterInitValidationRule ValidatesOnTargetUpdated="True" />
</Binding.ValidationRules>
</Binding>
</ComboBox.SelectedItem>
</ComboBox>
When the ValidationRule returns false
return ValidationResult(false,msg);
The Dependency Property bound to selected item is not updated.
Is there a way to force the binding to update the source ?
*Please if any one is going to raise a discussion here about
BindingExpression.UpdateSource() , please supply a working example, and not just blurt it out because it sounds like the solution ,
i do not intend to use Explicit mode on my Binding.
Further more i can easily code my way around this but a good .net programmer should thrive to write less code and use the built in mechanisms supplied by the .net framework ,
And that is the soul purpose of this question , is there a built in way of updating the source while
notifying of a DataError ?

How can I set the DataBinding to an arbitrary Property in XAML?

I have the following problem: I am designing an UserControl, a graded-color gauge. I have decieded to use the MVVM design patern, which turns out to be a good choice. However, I have the following problem. In the View XAML file, I try to convert a value to a color, using custtom converter, which needs 2 parameters. For this purpose, I use the MultiBinding:
<ItemsControl ItemsSource="{Binding Path=ViewData}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<Rectangle Height="2">
<Rectangle.Fill>
<MultiBinding Converter="{StaticResource colorConverter}">
<Binding Path="Value"/>
<Binding Source="{StaticResource Palette_ICOS}"/>
</MultiBinding>
</Rectangle.Fill>
</Rectangle>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
The thing is, that I don't want to use
{StaticResource Palette_ISO1}
as a second parameter, but a Property, which is a direct property of the DataContext and is not a property of the ViewData collection member. I have tried several ways to accomplish this scenario, but without signifficant success.
As last, I have tried the following:
<Binding Path="CurrentPallete"/>
and the CurrentPallete looks like:
public Palette CurrentPalette
{
get { return _currentPalette; }
set
{
_currentPalette = value;
}
}
i.e. a Property in the Class, whose instance is set as a DataContext of the main control, which hosts the ItemControl. What I get is a
[0x00000001] = {DependencyProperty.UnsetValue}
value in the Debugger, when the corresponding convertor is invoked,which probably means, that the Property cannot be found. Can anyone point out what is the way to achieve the desired effect? Thanks a lot!

<Binding Path="DataContext.Palette_ICOS"
RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=ItemsControl}" />

Have you tried
<Binding Path="Palette_ICOS"/>
If Palette_ICOS is a property in the current item's DataContext binding it should work.