Error template disappears from Cell after changing menu in HamburgerMenu

Describe the bug

Hello I have a WPF application where I use Prism and Mahapps. I have a DataGrid with model which implements INotifyDataErrorInfo Interface, after loading data to grid I see some cells with red border (the value is invalid there) but if go to another MenuItem in HamburgerMenu and then I back to the first MenuItem the red border are disappeared. I have tried using AdornerDecorator but it didn’t help. Then I have tried custom styles, and data temples for ErrorTemplate but it didn’t help too. But If I add following code, it works.

        <DataGrid.Resources>
            <Style  TargetType="{x:Type DataGridCell}" BasedOn="{StaticResource MahApps.Styles.DataGridCell}" >
                <Style.Triggers>
                    <MultiTrigger>
                        <MultiTrigger.Conditions>


                        </MultiTrigger.Conditions>


                    </MultiTrigger>
                </Style.Triggers>
            </Style>
        </DataGrid.Resources>

I have no idea why it behaves like that.

Steps to reproduce

1. Make model which implements INotifyDataErrorInfo .
2. Load some data to DataGrid, cells with incorrect data (validated by functions from INotifyDataErrorInfo ) should have red borders now.
3. Change View via HamburgerMenu
4. Back to View with Grid. Now red borders disappears.
5. Add the code from description. Now it should work.

Here is the View with DataGrid

<UserControl x:Class="PrismJPKEditor.Modules.JPK.Views.Declaration"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:prism="http://prismlibrary.com/"             
             prism:ViewModelLocator.AutoWireViewModel="True">

    
    
    <DataGrid GridLinesVisibility="All" ItemsSource="{Binding SessionContext.JPKDataSource.Declaration.Declarations}" AutoGenerateColumns="False" CanUserAddRows="False" CanUserDeleteRows="False" >

        <DataGrid.Resources>
            <Style  TargetType="{x:Type DataGridCell}" BasedOn="{StaticResource MahApps.Styles.DataGridCell}" >
                <Style.Triggers>
                    <MultiTrigger>
                        <MultiTrigger.Conditions>


                        </MultiTrigger.Conditions>


                    </MultiTrigger>
                </Style.Triggers>
            </Style>
        </DataGrid.Resources>


        <DataGrid.Columns>
            <DataGridTextColumn IsReadOnly="True" Width="auto" Header="Nazwa pola" Binding="{Binding FieldName}"/>
            <DataGridTextColumn IsReadOnly="True" Width="auto" Header="Opis pola" Binding="{Binding Description}"/>
            <DataGridTextColumn   IsReadOnly="False" Width="auto" Header="Wartość pola" Binding="{Binding GridValue, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}"/>
        </DataGrid.Columns>
    </DataGrid>
</UserControl>

Expected behavior

The error template should stays after changing view via HamburgerMenu.

Actual behavior

The error template disappears.

Environment

MahApps.Metro version: v2.0.0
Windows build number: Win10 1909 [Version 10.0.18363.836]
Visual Studio: 2019 16.6.0
Target Framework: .Net Core 3.1 (v4.5.2, v4.7.2)

[punker76]

@GWawrzeniecki The default cell style is set to the CellStyle of the DataGrid. So if you define a new global style in your App.xaml this style will not use (or only once). You can prevent this if you give your style a key and use this explicitly on your DataGrid.

<Style x:Key="SpecialCellStyle" TargetType="{x:Type DataGridCell}" BasedOn="{StaticResource MahApps.Styles.DataGridCell}" >
    <Style.Triggers>
        <MultiTrigger>
            <MultiTrigger.Conditions>
            </MultiTrigger.Conditions>
        </MultiTrigger>
    </Style.Triggers>
</Style>

<DataGrid Style="{StaticResource SpecialCellStyle}" ... />

If you use this style always then you can set this to a global DataGrid style.

<Style TargetType="{x:Type DataGrid}" BasedOn="{StaticResource {x:Type DataGrid}}">
  <Setter Property="CellStyle" Value="{StaticResource SpecialCellStyle}" />
</Style>

[timunie]

Hi @GWawrzeniecki

I made a simple test without prism and it works. https://github.com/GWawrzeniecki/JPK/pull/1 Maybe it has to do with PRISM?

Happy coding Tim