How to access value entered in a text box which is created in list view using data template

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C#

WPF

MVVM

Hello all,
I have created a **ListView** which displays one table.
And I have created 2 data templates which has one text box and button.
What I want is when user enters any value in textbox it should be passed as **command parameter** to the button
When I pass parameter as

CommandParameter="{Binding ElementName=txtQuantity}"

It gives me null in the parameter.

Here's the full code snippet

<ListView
            Margin="5,9,11,128"
            Name="listViewMedicineInfo"
            Grid.ColumnSpan="2"
            Grid.Row="1"
            Grid.Column="0"

            MinWidth="250" MinHeight="100"

            ItemsSource="{Binding ShowMedicineDetail}">
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="Loaded">
                    <i:InvokeCommandAction  Command="{Binding Path=ReturnMedicineInfoCommand}">
                    </i:InvokeCommandAction>
                </i:EventTrigger>

            </i:Interaction.Triggers>
            <ListView.View>
                <GridView>

                    <GridViewColumn   Header="Item Name" DisplayMemberBinding="{Binding Path=ItemName}" ></GridViewColumn>
                    <GridViewColumn Header="Brand Name" DisplayMemberBinding="{Binding Path=BrandName}"></GridViewColumn>
                    <GridViewColumn Header="Price" DisplayMemberBinding="{Binding Path=Price}"></GridViewColumn>
                    <GridViewColumn Header="In Stock" DisplayMemberBinding="{Binding Path=Quantity}"></GridViewColumn>
                    <GridViewColumn Header="Expiry Date" DisplayMemberBinding="{Binding Path=ExpiryDate}"></GridViewColumn>
                    <GridViewColumn Header="Quantity">
                        <GridViewColumn.CellTemplate>
                            <DataTemplate x:Name="dtTemplate">
                                <TextBox  Width="50" Text="{Binding TextBoxValue,Source={StaticResource medicinedetails}, UpdateSourceTrigger=PropertyChanged}" ></TextBox>
                            </DataTemplate>
                        </GridViewColumn.CellTemplate>

                    </GridViewColumn>
                    <GridViewColumn>
                        <GridViewColumn.CellTemplate>
                            <DataTemplate>
                                <Button Content="Update"
                                        Command="{Binding Path=DataContext.ReturnSelectedMedicineCommand,RelativeSource={RelativeSource AncestorType={x:Type ListView}}}"
                                        CommandParameter="{Binding ElementName=txtQuantity}">
                                </Button>
                            </DataTemplate>
                        </GridViewColumn.CellTemplate>
                    </GridViewColumn>
                </GridView>
            </ListView.View>
        </ListView>

Thanks for the help...
Cheers!