IDataErrorInfo onPropertyChange in DataGrid in WPF

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WPF

My class, which implements IDataErrorInfo, returns error message such way:

<pre lang="cs">public string Error
            {
                get
                {
                    StringBuilder sb = new StringBuilder();
                    if (NameOfWear.Length > 5 && Convert.ToInt16(Price) < 20000)
                    return sb.Append("Price is too small").ToString();
                    return sb.ToString();
                }
               }

This error is updated only at the start of application, or when I sort items in dataGrid, or when i call GridComponent.Reset(something like that). But I change this elemet from another textbox, both elements are binded . When I change textbox, element of dataGrid automatically changes too, and simle exceptions work onPropertyChanges and CollectionChanes,such as:

<pre lang="cs">public string this[string columnName]
               {
                   get
                   {
                       string result = "";
                       int i;
                       if (columnName == "NameOfWear")
                       {
                           if (string.IsNullOrWhiteSpace(NameOfWear))
                           {
                               result = "Enter any name";
                           }
                           else if (NameOfWear.Length < 3)
                           {
                               result = "Correct name plz";
                           }
                           else if(int.TryParse(NameOfWear,out i))
                           {
                               result="No numbers";
                           }
                       }
                       else if (columnName == "Price")
                       {
                           if (!int.TryParse(Price, out i))
                           {
                               result = "Only numbers";
                           }
                       }
                       return result;

How to make this exception to be displayed on PropertyChanged, not when GridReset,etc?
P.S. MY XAML:

<<pre lang="xml">Page x:Class="WpfBrowserApplication1.Page1"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:local="clr-namespace:WpfBrowserApplication1"
      mc:Ignorable="d"
      d:DesignHeight="300" d:DesignWidth="307"
      Title="Page1">
    <Page.Resources>
        <Style x:Key="ErrorStyle" TargetType="{x:Type TextBox}">
            <Style.Triggers>
                <Trigger Property="Validation.HasError" Value="true">
                    <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"/>
                    <Setter Property="BorderThickness" Value="0"/>
                    <Setter Property="Padding" Value="0"/>
                </Trigger>
            </Style.Triggers>
        </Style>
        <Style x:Key="RowStyle" TargetType="{x:Type DataGridRow}">
            <Style.Triggers>
                <Trigger Property="Validation.HasError" Value="true">
                    <Setter Property="BorderThickness" Value="1"/>
                    <Setter Property="BorderBrush" Value="Red"/>
                    <Setter Property="ToolTip" Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </Page.Resources>
    <Grid>
        <Grid.RowDefinitions>
        <RowDefinition Height="Auto"></RowDefinition>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <StackPanel  >
            <TextBox Margin="3" IsReadOnly="True">Название</TextBox>
            <TextBox Style="{StaticResource ResourceKey=ErrorStyle}" Margin="3"  Text="{Binding Path=wear.NameOfWear, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True, NotifyOnValidationError=True}"  ></TextBox>
            <TextBox Margin="3" IsReadOnly="True" >Цена</TextBox >
            <TextBox Style="{StaticResource ResourceKey=ErrorStyle}" Margin="3" Text="{Binding Path=wear.Price, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True, NotifyOnValidationError=True}"></TextBox>
            <StackPanel Orientation="Horizontal">
                <Button HorizontalAlignment="Stretch" Margin="3" Command="{Binding Path=AddRowCommand}" >Добавить поле</Button>
                <Button HorizontalAlignment="Stretch" Margin="3" Command="{Binding Path=RemoveRowCommand}" Content="RemoveRow"></Button>
            </StackPanel>
        </StackPanel>
        <DataGrid  RowStyle="{StaticResource RowStyle}"  ItemsSource="{Binding Path=Collection, ValidatesOnDataErrors=True, NotifyOnValidationError=True}"  SelectedItem="{Binding Path=wear, NotifyOnValidationError=True, ValidatesOnDataErrors=True}" IsSynchronizedWithCurrentItem="True" AutoGenerateColumns="False" HorizontalAlignment="Stretch"  Name="dataGrid1" VerticalAlignment="Stretch" IsReadOnly="False" Grid.Row="1">
            <DataGrid.RowValidationRules>
                <DataErrorValidationRule ValidationStep="UpdatedValue"  ValidatesOnTargetUpdated="True">
                </DataErrorValidationRule>
            </DataGrid.RowValidationRules>
            <DataGrid.Columns >
                <DataGridTextColumn  Header="Name" Binding="{Binding Path=NameOfWear, ValidatesOnDataErrors=True, NotifyOnValidationError=True}" Width="*"></DataGridTextColumn>
                <DataGridTextColumn  Header="Price" Binding="{Binding Path=Price, ValidatesOnDataErrors=True, NotifyOnValidationError=True}" Width="*"></DataGridTextColumn>
                </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Page>

P.S.2 Everything works fine,except this.
P.S.3 Sorry for bad English /