Binding an element inside a UserControl inside a tabControl does not work (WPF)

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C#

WPF

Hi To make a long story short, I cannot bind a textbox correctly.

This is photo of my program:
The Link[^]

I have a tabControl. Inside the tabControl, there are several tabs that are defined by a template:

<TabControl.ContentTemplate>
    <DataTemplate>
         <myUserControl:UserControlTabpageContent>
         </myUserControl:UserControlTabpageContent>
    </DataTemplate>
</TabControl.ContentTemplate>

They contain a user control.
The tab controller is binded to a collection of this class:

[Serializable]
public class TabpageItem
{
    public string Title { get; set; }
    private ObservableCollection<InfoItem> infoItemCollection = new ObservableCollection<InfoItem>();
    public ObservableCollection<InfoItem> InfoItemCollection
    {
        get { return infoItemCollection; }
    }
    [NonSerialized]
    private ObservableCollection<InfoItem> infoItemSerachResult = new ObservableCollection<InfoItem>();
    public ObservableCollection<InfoItem> InfoItemSerachResult
    {
        get { return infoItemSerachResult; }
    }
    [NonSerialized]
    private string _SerachString;
    public string SerachString
    {
        set
        {
            _SerachString = value;
        }
        get
        {
            return _SerachString;
        }
    }
}

Inside the user control I have a textbox. When the user writes something inside the textbox, the text clears by changing between tabs. If I adjust some properties, then the text does not clear but is the same for all tabs. as if all tabs are using the same data, while I like textbox of each tab operates independent.

This is WPF source of my main window:

<Window x:Class="InfoManager.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:myUserControl="clr-namespace:InfoManager.Presentation_Layer"
        Title="MainWindow" Height="350" Width="507" Closed="Window_Closed">
        <Grid>
        <TabControl x:Name="tabControlMain" Margin="1,1,48,1" DataContext="{Binding}" Grid.RowSpan="2" Grid.ColumnSpan="2">
            <TabControl.ItemTemplate>
                <DataTemplate DataType="TabpageItem">
                    <TextBlock Text="{Binding Title}">
                        <TextBlock.ContextMenu>
                            <ContextMenu>
                                <MenuItem Header="Remove" Click="MenuItem_Remove_Click">
                                    <MenuItem.Icon>
                                        <Image Width="20" Height="20"  Source="..\Resources\remove.png" Stretch="Fill" />
                                    </MenuItem.Icon>
                                </MenuItem>
                                <MenuItem Header="Rename" >
                                    <MenuItem.Icon>
                                        <Image Height="20"  Source="..\Resources\rename.png" Stretch="UniformToFill" />
                                    </MenuItem.Icon>
                                    <StackPanel Orientation="Horizontal">
                                        <TextBlock Text="Rename to:   " VerticalAlignment="Center"></TextBlock>
                                        <TextBox Text="{Binding Title}" GotMouseCapture="TextBox_GotMouseCapture"></TextBox>
                                    </StackPanel>
                                </MenuItem>
                            </ContextMenu >
                        </TextBlock.ContextMenu>
                    </TextBlock>
                </DataTemplate>
            </TabControl.ItemTemplate>
                <TabControl.ContentTemplate>
                    <DataTemplate>
                                <myUserControl:UserControlTabpageContent></myUserControl:UserControlTabpageContent>
                    </DataTemplate>
                </TabControl.ContentTemplate>
            <TabItem Header="tabItem1" Name="tabItem1" >
                <myUserControl:UserControlTabpageContent></myUserControl:UserControlTabpageContent>
            </TabItem>
        </TabControl>
        <Button Width="30" Height="30" HorizontalAlignment="Right"  Name="buttonAddTab" VerticalAlignment="Top" Margin="0,5,5,0" Click="buttonAddTab_Click" Grid.Column="1">
        <Image Source="..\resources\add.png" Stretch="UniformToFill"></Image>
        </Button>
    </Grid>
</Window>

and this is WPF source of my user control:

<UserControl
             x:Class="InfoManager.Presentation_Layer.UserControlTabpageContent"
             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"
             mc:Ignorable="d"
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <Grid Name="grid1">
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="*"/>
            </Grid.RowDefinitions>
            <Grid Name="grid2">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="Auto" />
                    <ColumnDefinition Width="*" />
                </Grid.ColumnDefinitions>
                <TextBlock Name="textBlock1" Text="Select by tags:" VerticalAlignment="Center" HorizontalAlignment="Left" Margin="10" />
                <TextBox Grid.Column="1" Text="{Binding SerachString?????????????????}"  Name="textBoxSelectionTags"  VerticalAlignment="Center" Margin="10" />
            </Grid>
            <ListView Grid.Row="1" Name="listView1" Margin="10" />
        </Grid>
    </Grid>
</UserControl>

I put the source code here, in case it is needed:
http://www.megaupload.com/?d=S0U05X63[^]

Thanks