Null reference exception in designer page with custom controls

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I'm having custom control of Grid which is derived from Control. Getting exception in designer page when merged the styles of custom controls in xaml. if i'm not merged the styles of custom control, then this exception will not be thrown.

Please find the stack trace below:

C#

at System.Windows.StyleHelper.GetInstanceValue(UncommonField`1 dataField, DependencyObject container, FrameworkElement feChild, FrameworkContentElement fceChild, Int32 childIndex, DependencyProperty dp, Int32 i, EffectiveValueEntry& entry)
   at System.Windows.StyleHelper.GetChildValueHelper(UncommonField`1 dataField, ItemStructList`1& valueLookupList, DependencyProperty dp, DependencyObject container, FrameworkObject child, Int32 childIndex, Boolean styleLookup, EffectiveValueEntry& entry, ValueLookupType& sourceType, FrameworkElementFactory templateRoot)
   at System.Windows.StyleHelper.GetChildValue(UncommonField`1 dataField, DependencyObject container, Int32 childIndex, FrameworkObject child, DependencyProperty dp, FrugalStructList`1& childRecordFromChildIndex, EffectiveValueEntry& entry, ValueLookupType& sourceType, FrameworkElementFactory templateRoot)
   at System.Windows.StyleHelper.GetValueFromStyleOrTemplate(FrameworkObject fo, DependencyProperty dp, EffectiveValueEntry& entry)
   at System.Windows.StyleHelper.ApplyStyleOrTemplateValue(FrameworkObject fo, DependencyProperty dp)
   at System.Windows.StyleHelper.InvalidateContainerDependents(DependencyObject container, FrugalStructList`1& exclusionContainerDependents, FrugalStructList`1& oldContainerDependents, FrugalStructList`1& newContainerDependents)
   at System.Windows.StyleHelper.DoStyleInvalidations(FrameworkElement fe, FrameworkContentElement fce, Style oldStyle, Style newStyle)
   at System.Windows.StyleHelper.UpdateStyleCache(FrameworkElement fe, FrameworkContentElement fce, Style oldStyle, Style newStyle, Style& styleCache)
   at System.Windows.FrameworkElement.OnStyleChanged(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.InvalidateProperty(DependencyProperty dp, Boolean preserveCurrentValue)
   at System.Windows.FrameworkElement.UpdateStyleProperty()
   at System.Windows.FrameworkElement.OnInitialized(EventArgs e)
   at System.Windows.FrameworkElement.TryFireInitialized()
   at System.Windows.FrameworkElement.EndInit()
   at MS.Internal.Xaml.Runtime.ClrObjectRuntime.InitializationGuard(XamlType xamlType, Object obj, Boolean begin)
   at System.Xaml.XamlObjectWriter.Logic_EndInit(ObjectWriterContext ctx)
   at System.Xaml.XamlObjectWriter.WriteEndObject()
   at System.Xaml.XamlWriter.WriteNode(XamlReader reader)
   at System.Windows.FrameworkTemplate.LoadTemplateXaml(XamlReader templateReader, XamlObjectWriter currentWriter)
   at System.Windows.FrameworkTemplate.LoadTemplateXaml(XamlObjectWriter objectWriter)
   at System.Windows.FrameworkTemplate.LoadOptimizedTemplateContent(DependencyObject container, IComponentConnector componentConnector, IStyleConnector styleConnector, List`1 affectedChildren, UncommonField`1 templatedNonFeChildrenField)
   at System.Windows.FrameworkTemplate.LoadContent(DependencyObject container, List`1 affectedChildren)
   at System.Windows.StyleHelper.ApplyTemplateContent(UncommonField`1 dataField, DependencyObject container, FrameworkElementFactory templateRoot, Int32 lastChildIndex, HybridDictionary childIndexFromChildID, FrameworkTemplate frameworkTemplate)
   at System.Windows.FrameworkTemplate.ApplyTemplateContent(UncommonField`1 templateDataField, FrameworkElement container)
   at System.Windows.FrameworkElement.ApplyTemplate()
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Border.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
   at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV, Boolean& hasDesiredSizeUChanged)
   at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV)
   at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
   at System.Windows.UIElement.Measure(Size availableSize)
   at System.Windows.Controls.Control.MeasureOverride(Size constraint)

Can anyone help to resolve this issue?

Posted 29-Jun-15 19:55pm

Member 11267379

Updated 29-Jun-15 21:14pm

Herman<T>.Instance

v2

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Comments

Herman<T>.Instance 30-Jun-15 3:14am

I think only you can at this moment. Too less information

virusstorm 30-Jun-15 12:23pm

This is a fun one I've run into many times and it is pain to debug. Take a close look at all of the child controls, specifically inside your control's constructor or load event. If you are doing any action that requires an object to exist, but won't until run time, you will get this error. Take a look at using this:
DesignerProperties.GetIsInDesignMode(this)

Member 11267379 1-Jul-15 0:26am

Hi,

Thanks. i will check all the child controls.

DesignProperties.GetIsInDesignMode(this) - what is the use of this? and how this help for me to find a rootcause of the issue?

Jan Bakker 1-Jul-15 9:01am

in your custom control,
Put a
Try
{
InitializeComponent();
.....
}
Catch (Exception ex)
{
}
in your constructor or/and loaded event.
(Put a breakpoint in the Catch)

Jitesh Hirani 6-Jul-15 6:08am

It might be possible that you have assigned some values to your control that decide the behaviour of control and is not available at design time / compile time(for e.g. ApplicationSettings.EmployeeDesign.RowCount to Grid total columns) thus invoking a exception. Try identifying such values, might help you out.

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