Develop Reference

How do I write inline xaml for a MultiBinding converter?

How do I include the second binding? Where do the brackets and commas go?
There are five thousand examples that show how to do it in xml but nothing about how this should appear inline.
NOT THIS
<TextBlock>
<TextBlock.Text>
<MultiBinding StringFormat="{}{0:F1}{1:F1}">
<Binding Path="A" />
<Binding Path="B" />
</MultiBinding>
</TextBlock.Text>
</TextBlock>
THIS
<StackPanel Grid.Column="0"
Orientation="Vertical"
HorizontalAlignment="Left"
Visibility="{MultiBinding Converter={StaticResource multi_bool_vis_conv},
Bindings={Binding LabelFormat.HasLotMaskShiftCode}}">
I need to pass a second binding LabelFormat.HasSomeOtherCode. How do I include that second binding?

Assuming multi_bool_vis_conv implements the interface IMultiValueConverter and you handle the different parameters by indexing off of the value array, the binding should look like this:
<MultiBinding Converter="{StaticResource YourConverter}">
<Binding Path="YourProperty1"/>
<Binding Path="YourProperty2"/>
</MultiBinding>
I assume you want this on one line ("in-line") because you want to set the binding on the StackPanel's Visiblity property and your not sure how to do that in a multi-line way...
You can break it out like this:
<StackPanel>
<StackPanel.Visibility>
<MultiBinding Converter="{StaticResource YourConverter}">
<Binding Path="YourProperty1" />
<Binding Path="YourProperty2" />
</MultiBinding>
</StackPanel.Visibility>
</StackPanel>
The only other way I can see to do what you want is to roll your own StackPanel and include dependency properties for each of the bindings you want. You can then bind each of those on their own line and forgo a binding on the Visibility property all-together, instead opting to control the visibility in the code-behind of your custom control.

ConvertBack is not called

I'm trying to write a universal control in which I can pass different data models (all implement INotifyPropertyChanged) with a converter. The data is passed in the control without problems and is displayed correctly (some of it also uses IMultivalueConverts, which work flawlessly). Although the data is modified, the IMultiValueConverter of the MainControl is not called.
The universal control should just show rectangles calculated from coordinates in an ObservableCollection.
I put DebugConverters on all bindings, and everything seems to be updated except the ConvertBack to the top. The SourceUpdate from the ListBox is also called.
I tried this converter with different NotifyOn...Updated, Mode and UpdateSourceTrigger, I always see the values changing in the control, but never the ConvertBack of the Main Control.
The partial data template used (Updates are done correctly), all the DegreeTo... converters are called both ways
<DataTemplate x:Key="RectangleWithLabel">
<Canvas IsHitTestVisible="True">
<Rectangle x:Name="RectangleROI" MouseLeftButtonDown="myCanvas_PreviewMouseLeftButtonDown" >
<!--
<Rectangle.Visibility>
<Binding Path="ROI" Converter="{StaticResource NullToVisibilityConverter}"/>
</Rectangle.Visibility>
-->
<Canvas.Left>
<MultiBinding Converter="{StaticResource DegreeToScreenPixelConverterH}" Mode="TwoWay" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True" UpdateSourceTrigger="PropertyChanged" >
<Binding Path="ROI.Begin.PosH" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True" />
<Binding Path="DataContext.UsedCoordinateSystem" RelativeSource="{RelativeSource FindAncestor, AncestorType={x:Type UserControl}}" NotifyOnSourceUpdated="True" Mode="TwoWay" NotifyOnTargetUpdated="True" UpdateSourceTrigger="PropertyChanged" />
</MultiBinding>
</Canvas.Left>
<Canvas.Top>
<MultiBinding Converter="{StaticResource DegreeToScreenPixelConverterV}" Mode="TwoWay" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True" UpdateSourceTrigger="PropertyChanged">
<Binding Path="ROI.Begin.PosV" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True" />
<Binding Path="DataContext.UsedCoordinateSystem" RelativeSource="{RelativeSource FindAncestor, AncestorType={x:Type UserControl}}" NotifyOnSourceUpdated="True" Mode="TwoWay" NotifyOnTargetUpdated="True" UpdateSourceTrigger="PropertyChanged"/>
</MultiBinding>
</Canvas.Top>
<Rectangle.Width>
<MultiBinding Converter="{StaticResource DegreeToScreenPixelWidthConverter}" Mode="TwoWay" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True" UpdateSourceTrigger="PropertyChanged">
<Binding Path="ROI.Begin.PosH" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True" />
<Binding Path="ROI.End.PosH" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True" />
<Binding Path="DataContext.UsedCoordinateSystem" RelativeSource="{RelativeSource FindAncestor, AncestorType={x:Type UserControl}}" NotifyOnSourceUpdated="True" Mode="TwoWay" NotifyOnTargetUpdated="True"/>
</MultiBinding>
</Rectangle.Width>
<Rectangle.Height>
<MultiBinding Converter="{StaticResource DegreeToScreenPixelHeightConverter}" Mode="TwoWay" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True" UpdateSourceTrigger="PropertyChanged">
<Binding Path="ROI.Begin.PosV" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True"/>
<Binding Path="ROI.End.PosV" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True" />
<Binding Path="DataContext.UsedCoordinateSystem" RelativeSource="{RelativeSource FindAncestor, AncestorType={x:Type UserControl}}" NotifyOnSourceUpdated="True" Mode="TwoWay" NotifyOnTargetUpdated="True" UpdateSourceTrigger="PropertyChanged"/>
</MultiBinding>
</Rectangle.Height>
<Rectangle.Fill>#33FF0000</Rectangle.Fill>
<Rectangle.Stroke>#FF00FF00</Rectangle.Stroke>
<Rectangle.IsHitTestVisible>true</Rectangle.IsHitTestVisible>
</Rectangle>
The List View containing all the data:
<ListView ItemsSource="{Binding Rectangles, Mode=TwoWay, NotifyOnTargetUpdated=True, NotifyOnSourceUpdated=True, NotifyOnValidationError=True, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True, ValidatesOnExceptions=True}" x:Name="listBox" Width="{Binding ActualWidth, ElementName=ImageControl, Mode=OneWay,UpdateSourceTrigger=PropertyChanged}" Height="{Binding ActualHeight, ElementName=ImageControl, Mode=OneWay,UpdateSourceTrigger=PropertyChanged}" Background="{x:Null}" BorderBrush="{x:Null}" Foreground="{x:Null}" ItemTemplate="{StaticResource RectangleWithLabel}" MouseMove="ListBox_MouseMove" DataContextChanged="ListBox_DataContextChanged" SourceUpdated="ListBox_SourceUpdated" IsSynchronizedWithCurrentItem="True" TargetUpdated="ListBox_TargetUpdated" />
The call to the ImageViewer from the parent, here the converter is called on the way to the ImageViewer, but the ConvertBack is never called:
<common:ImageViewer x:Name="ctrlImage" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" >
<common:ImageViewer.DataContext>
<MultiBinding Converter="{StaticResource ConverterWhichIsOnlyCalledOneWay}" Mode="TwoWay" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True" UpdateSourceTrigger="PropertyChanged">
<Binding Path="." UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True"/>
</MultiBinding>
</common:ImageViewer.DataContext>
</common:ImageViewer>
How can I get the ConvertBack to be called?
EDIT:
I made an overview of the controls and the converters. I think I was wrong, that the ConvertBack should be called, everything is updating, even without the big converter. But I'm still stuck when adding some elements to the ObservableCollection. When I add some values, the values appear in the DataContext of the MainWindow. But the Converter is not triggered. When I add the Observable.Count as Binding to the Big Converter, the update is triggered, but all bindings are lost.
Changes from the original code were: Changing all internal variables to DependencyProperties, this made updates reliable for the single entries in the ObservableCollection.
Overview of the GUI and the used converters

Time to answer the question myself:
I was wrong when assuming that a changes travels down throught the converter when there is a direct connection between two elements.
So if I have an element (just consider it as a leave of a tree) in a deeply nested and it is once displayed once through a converter (which changes some other objects) and the same time without a converter, the element is updated without calling the converter. WPF is so clever to see that the value is the same and does not pipe the change through the converter up and down.

What is the order of setting properties in XAML?

I have a TextBlock with two properties (Text and Foreground) bound to the same ViewModel property.
Both also have converters. One of the converters checks the Text property and returns a 'dash' if the value is NaN. The other checks that the value is above, below or equals zero and accordingly sets the foreground to different colors.
XAML example:
<TextBlock>
<TextBlock.Text>
<Binding Path="AvgDistance" StringFormat="{}{0:N1}"
Converter="{x:Static converter:ValueToDash.Instance}"/>
</TextBlock.Text>
<TextBlock.Foreground>
<MultiBinding Converter="{x:Static converter:ValueToColor.Instance}">
<Binding Path="AvgDistance"/>
<Binding ElementName="currentPeriod" Path="IsChecked" />
</MultiBinding>
</TextBlock.Foreground>
</TextBlock>
Now I need that the ValueToDash converter fired before the ValueToColor converter, but it is always vice versa.
The Foreground property seems to be always set first, and only then the Text property is set.
Why is it so? And is it possible to reverse the order of setting?

You shouldn't rely on the order in which the properties are being set.
What you could do instead is to add another binding to your MultiBinding that binds to the Text property of the TextBlock:
<TextBlock>
<TextBlock.Text>
<Binding Path="AvgDistance" StringFormat="{}{0:N1}"
Converter="{x:Static converter:ValueToDash.Instance}"/>
</TextBlock.Text>
<TextBlock.Foreground>
<MultiBinding Converter="{x:Static converter:ValueToColor.Instance}">
<Binding Path="AvgDistance"/>
<Binding ElementName="currentPeriod" Path="IsChecked" />
<Binding Path="Text" RelativeSource="{RelativeSource Self}"/>
</MultiBinding>
</TextBlock.Foreground>
</TextBlock>
Then the ValueToColor converter will be invoked (again) whenever the Text property is set to some new value.

Enforce validation on a TexBox when text changes in WPF

I'm using Validation on TextBox as follows
<TextBox BorderThickness="1" Style="{DynamicResource TextBoxInError}"
Validation.ErrorTemplate="{StaticResource ValidationTemplate}">
<TextBox.Text>
<Binding Path="TimeBeforeDeletingPicture" Mode="TwoWay">
<Binding.ValidationRules>
<helpers:TimeBeforeDeletingRule/>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
The validation fires when I leave the TextBox (apparently when it looses focus), I want to validate the input every time the text changes, I'm using MVVM so I don't want to mess with events, what's the correct clean way to achieve that.

Set UpdateSourcetrigger as follows
<TextBox.Text>
<Binding Path="TimeBeforeDeletingPicture" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged"/>

StringFormat and Multibinding with Label

I would like to use StringFormat to do someting like this :
<Label x:Name="myLabel">
<Label.Content>
<Multibinding StringFormat="{}{0} - {1}">
<Binding Path="Lib1" />
<Binding Path="Lib2" />
</MultiBinding>
</Label.Content>
</Label>
However, it's doesn't work and I got this error instead :
MultiBinding failed because it has no valid Converter. MultiBindingExpression:target element is 'Label' (Name='myLabel'); target property is 'Content' (type 'Object')
Is there any way to make this code work ?

You cant bind this because you are trying to bind a string to an object which wont work because StringFormat requires its target to be a string type. You can get around this by either using a TextBlock instead (which has a Text property) or putting the Textblock as the child of the Label:
<Label x:Name="myLabel">
<Label.Content>
<TextBlock>
<TextBlock.Text>
<MultiBinding StringFormat="{}{0} - {1}">
<Binding Path="Lib1" />
<Binding Path="Lib2" />
</MultiBinding>
</TextBlock.Text>
</TextBlock>
</Label.Content>
</Label>

For those wondering you can also leave the <Label.Content> tag from Leom Burke's answer. This saves another two lines of code.
<Label x:Name="myLabel">
<TextBlock>
<TextBlock.Text>
<MultiBinding StringFormat="{}{0} - {1}">
<Binding Path="Lib1" />
<Binding Path="Lib2" />
</MultiBinding>
</TextBlock.Text>
</TextBlock>
</Label>

<Label>
<AccessText>
<MultiBinding StringFormat="{x:Static properties:Resources.MyText}">
<Binding Path="MyObj.MyProp" Mode="OneTime"/>
</MultiBinding>
</AccessText>
</Label>
Where Resources.MyText can hold anything like "Fox jumps over {0}."