Multiple TextBoxes but same property - wpf

Question

I have textbox A on tab A and textbox B on tab B. I databind them to the same property. I use the same binding:
<TextBox>
<TextBox.Text>
<Binding Path=ValueA UpdateSourceTrigger="LostFocus">
<Binding.ValidationRules>
<local:MyValidationRules />
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
But there is a problems. if the value in textbox A is invalidate, it will not update the property in the source. But it will looks find if the user switches to tab b. Basically, the validation rule is blocking the updates from changing the source.
I tried to bind textbox b to textbox a. The problem was the validation rules seem to work for only textbox a, but not b.

Answer 1

Design wise, if the user entered an invalid value in textbox A, you do not want to show it on textbox B, since it's invalid. If I were you I would deny the user access to tab B until the textbox A is valid
Here is an example :
View:
<Grid>
<Grid.Resources>
<local:TabSelectionConverter x:Key="tabSelectionConverter"/>
</Grid.Resources>
<TabControl x:Name="myTabControl">
<TabItem x:Name="TabA" Header="Tab A">
<TextBox x:Name="TextBoxA" Text="{Binding MyTextProperty}" Height="20"/>
</TabItem>
<TabItem x:Name="TabB" Header="Tab B">
<TextBox x:Name="TextBoxB" Text="{Binding MyTextProperty}" Height="20"/>
</TabItem>
<i:Interaction.Triggers>
<i:EventTrigger EventName="SelectionChanged">
<i:InvokeCommandAction Command="{Binding TabSelectionChangedCommand}">
<i:InvokeCommandAction.CommandParameter>
<MultiBinding Converter="{StaticResource tabSelectionConverter}">
<Binding ElementName="myTabControl"/>
<Binding ElementName="TextBoxA" Path="Text"/>
</MultiBinding>
</i:InvokeCommandAction.CommandParameter>
</i:InvokeCommandAction>
</i:EventTrigger>
</i:Interaction.Triggers>
</TabControl>
</Grid>
Converter that will create an object with all the neccassary elements inroder to validate an deny access to second tab:
public class TabSelectionConverter : IMultiValueConverter
{
#region IMultiValueConverter Members
public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return new TabSelectionParameters
{
MainTab = values[0] as TabControl,
InputText = values[1] as string
};
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
#endregion
}
public class TabSelectionParameters
{
public TabControl MainTab { get; set; }
public string InputText { get; set; }
}
And your logic in the ViewModel:
public class MainWindowViewModel : NotificationObject
{
private string myTextProperty;
public MainWindowViewModel()
{
TabSelectionChangedCommand = new DelegateCommand<TabSelectionParameters>(parameters =>
{
if (parameters.InputText == string.Empty) // Here goes the validation of the user input to TextBoxA
{
// Deny selection of tab B by returning the selection index to Tab A
parameters.MainTab.SelectedIndex = 0;
}
});
}
public DelegateCommand<TabSelectionParameters> TabSelectionChangedCommand { get; set; }
public string MyTextProperty
{
get
{
return myTextProperty;
}
set
{
myTextProperty = value;
RaisePropertyChanged(() => MyTextProperty);
}
}
}
Hope this helps