Disabling button in listview grid in wpf depends on row count

<StackPanel x:Uid="StackPanel_2"  Grid.Row="1" Margin="1,0,0,0" x:Name="raham">
                    <ListView x:Uid="lstPurchaseOrder1" x:Name="lstPurchaseOrder1"  HorizontalAlignment="Stretch"
                                    Margin="10,10,10,5"
                                  Localization.Attributes="$Content(Ignore)">
                        <ListView.View>
                            <GridView x:Uid="grdPurchaseOrder1" x:Name="grdPurchaseOrder1" Localization.Attributes="$Content(Ignore)">
                                <GridViewColumn x:Uid="GridViewColumn_1" x:Name="GridViewColumn_1">
                                    <GridViewColumnHeader x:Uid="GridViewColumnHeader1" Width="200" HorizontalAlignment="Left"
                                                    Localization.Attributes="SortBinding(Ignore)"        
                                                    Localization.Comments="$Content(Column Header for Attribute)">
                                        Section
                                    </GridViewColumnHeader>

                                    <GridViewColumn.CellTemplate>

                                        <DataTemplate x:Uid="DataTemplate_1">
                                           <TextBox x:Uid="txtSectionName" Name="txtSectionName" Text="{Binding Mode=TwoWay, Path=SectionName}" HorizontalAlignment="Left"
                                                      Width="100"  MaxLength="30" Localization.Attributes="$Content(Ignore) Text(Ignore)" LostFocus="btnSave_Click" />

                                        </DataTemplate>

                                    </GridViewColumn.CellTemplate>
                                </GridViewColumn>
                                <GridViewColumn x:Uid="GridViewColumn_2" x:Name="PartnerPOColumn">
                                    
                                   
                                    <GridViewColumnHeader x:Uid="GridViewColumnHeader2" Padding="5,2"   HorizontalAlignment="Left"  
                                                    Localization.Attributes="SortBinding(Ignore)"        
                                                    Localization.Comments="$Content(Column Header for Operator)">
                                        Partner Purchase Order
                                    </GridViewColumnHeader>
                                    <GridViewColumn.CellTemplate>
                                        <DataTemplate x:Uid="DataTemplate_2">
                                           <TextBox x:Uid="txtPartnerPO"   Name="txtPartnerPO" Text="{Binding Mode=TwoWay,Path=PartnerPO}" HorizontalAlignment="Left"
                                                           Width="100"   MaxLength="30" Localization.Attributes="$Content(Ignore) Text(Ignore)"/>
                                        </DataTemplate>
                                    </GridViewColumn.CellTemplate>
                                </GridViewColumn>
                                <GridViewColumn x:Uid="GridViewColumn_3">
                                    <GridViewColumnHeader x:Uid="GridViewColumnHeader3" Width="200" HorizontalAlignment="Left"
                                                    Localization.Attributes="SortBinding(Ignore)"        
                                                    Localization.Comments="$Content(Column Header for Value)">
                                        Customer Purchase Order
                                    </GridViewColumnHeader>
                                    <GridViewColumn.CellTemplate>
                                        <DataTemplate x:Uid="DataTemplate_3">
                                           <TextBox x:Uid="txtCustomerPO"  Name="txtCustomerPO" Text="{Binding Mode=TwoWay, Path=CustomerPO}" HorizontalAlignment="Left"
                                                           Width="100"  MaxLength="30" Localization.Attributes="$Content(Ignore) Text(Ignore)"/>
                                        </DataTemplate>
                                    </GridViewColumn.CellTemplate>
                                </GridViewColumn>
                               <GridViewColumn x:Uid="GridViewColumn_4">
                                    <GridViewColumnHeader x:Uid="GridViewColumnHeader4" Width="100"   HorizontalAlignment="Left"
                                                  >
                                        Action
                                    </GridViewColumnHeader>
                                    <GridViewColumn.CellTemplate>
                                        <DataTemplate x:Uid="DataTemplate_4">

                                           <Button x:Uid="btnRemoveAll" x:Name="btnRemoveAll" Margin="2,0,2,2" Width="100" HorizontalAlignment="Right">Remove</Button>
                                        </DataTemplate>
                                    </GridViewColumn.CellTemplate>
                                </GridViewColumn>
                            </GridView>
                        </ListView.View>
                    </ListView>