Well, it had to happen some day.

I’ve found an issue in a project we are using @ work. I’ve created a fix and I want to share it!.

So this project is hosted on github, and it is indeed simple to add fixes.

Just follow these steps :

1. Fork the project
2. Create a feature / fix branch
3. Apply fix.
4. Push to github.
5. View this branch on github
6. Push the “Create Pull Request” button

It will then show you if it can be merged at all. Add some information and you are done!

better details

The fix.

I’ve created a rather simple fix. We are using the “Fluent.Ribbon” for a modern look and feel. But some of our controls are still winforms. There is nothing wrong with winforms, but a mixture of wpf and winforms is not always ideal.

Anyway, we have a combobox in our ribbon and when a winforms control has focus and you try to open this combobox in your ribbon, it acts up.  repro : 

Fluent.Ribbon WindowsFormsHost_Issue

1 file(s) 72.47 KB

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We have found this message in the debug window:

System.Windows.Data Error: 8 : Cannot save value from target back to source. BindingExpression:Path=IsDropDownOpen; DataItem=’ComboBox’ (Name=’StyleCbx’); target element is ‘ToggleButton’ (Name=’ToggleButton’); target property is ‘IsChecked’ (type ‘Nullable`1′) NullReferenceException:’System.NullReferenceException: Object reference not set to an instance of an object.
at Fluent.ComboBox.OnDropDownOpened(EventArgs e)
at System.Windows.Controls.ComboBox.OnIsDropDownOpenChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
at MS.Internal.Data.PropertyPathWorker.SetValue(Object item, Object value)
at MS.Internal.Data.ClrBindingWorker.UpdateValue(Object value)
at System.Windows.Data.BindingExpression.UpdateSource(Object value)’

Turns out that the fix was rather simple. The combobox of fluent expected the Keyboard.FocusedElement, to always be non-null.

Well this is not the case when dealing with a mixed technology window. So the fix was created and a pull request has been offered.