Memory leak due to GridView in Windows Store apps - xaml

Question

I have the following GridView
<GridView
x:Name="itemGridView"
AutomationProperties.AutomationId="ItemsGridView"
AutomationProperties.Name="Items"
TabIndex="1"
Grid.RowSpan="2"
Padding="116,136,116,46"
SelectionMode="Single"
IsSwipeEnabled="false"
Visibility="Collapsed">
<GridView.ItemTemplate>
<DataTemplate>
<!--<Border BorderBrush="DarkSeaGreen" BorderThickness="1">-->
<Grid Background="{Binding objBackgroundColor}" Opacity="1" Width="400" Height="80">
<Grid.RowDefinitions>
<RowDefinition Height="30"></RowDefinition>
<RowDefinition Height="*"></RowDefinition>
</Grid.RowDefinitions>
<Grid Grid.Row="0">
<TextBlock Text="{Binding objCustomTestPaper.Name}" TextWrapping="Wrap" FontWeight="SemiBold" VerticalAlignment="Top" Foreground="{Binding objForegroundColor}" Style="{StaticResource TitleTextStyle}" FontSize="20" MaxHeight="25" Margin="10,5,10,0" />
</Grid>
<Grid Grid.Row="1">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto"></ColumnDefinition>
<ColumnDefinition Width="*"></ColumnDefinition>
<ColumnDefinition Width="120"></ColumnDefinition>
</Grid.ColumnDefinitions>
<!--<Image Grid.Column="0" Height="35" VerticalAlignment="Center" HorizontalAlignment="Center" Source="Assets/paper.png"></Image>-->
<StackPanel Grid.Column="0" Margin="5,7,0,0">
<callisto:Rating FontStretch="SemiCondensed" ItemCount="5" Value="{Binding objCustomTestPaper.TestRating}" FontWeight="Light" VerticalAlignment="Bottom" Margin="0,2,5,1" Background="Transparent" HorizontalAlignment="Left" Foreground="{Binding objForegroundColor}" IsHitTestVisible="False" FontSize="12" >
</callisto:Rating>
<StackPanel Orientation="Horizontal" HorizontalAlignment="Left">
<TextBlock Text="Attempted by others:" Margin="4,0,0,0" FontSize="12" FontWeight="Light" Foreground="{Binding objForegroundColor}"></TextBlock>
<TextBlock Text="{Binding objCustomTestPaper.AttemptCount}" FontWeight="SemiBold" Margin="5,0,0,0" FontSize="12" Foreground="{Binding objForegroundColor}"></TextBlock>
<TextBlock Text="times" Margin="3,0,0,0" FontSize="12" FontWeight="Light" Foreground="{Binding objForegroundColor}"></TextBlock>
</StackPanel>
</StackPanel>
<StackPanel VerticalAlignment="Stretch" Grid.Column="2" Margin="0,0,0,0" >
<StackPanel Orientation="Horizontal" HorizontalAlignment="Left" VerticalAlignment="Center">
<TextBlock Text="Time:" FontSize="16" Foreground="{Binding objForegroundColor}" VerticalAlignment="Bottom" FontWeight="SemiLight"></TextBlock>
<TextBlock Text="{Binding strTestDuration}" Margin="5,0,0,0" FontSize="18" VerticalAlignment="Bottom" Foreground="{Binding objForegroundColor}" FontWeight="SemiLight"></TextBlock>
</StackPanel>
<StackPanel Margin="0,2,0,0" Orientation="Horizontal" HorizontalAlignment="Left" VerticalAlignment="Center">
<TextBlock Text="Points:" FontSize="16" Margin="0,0,0,0" VerticalAlignment="Bottom" Foreground="{Binding objForegroundColor}" FontWeight="SemiLight"></TextBlock>
<TextBlock Text="{Binding objCustomTestPaper.TotalMarks}" Margin="5,0,0,0" VerticalAlignment="Bottom" FontSize="18" Foreground="{Binding objForegroundColor}" FontWeight="SemiLight"></TextBlock>
</StackPanel>
</StackPanel>
</Grid>
</Grid>
</DataTemplate>
</GridView.ItemTemplate>
</GridView>
It is working fine and loads data successfully but When I press back button the data remains in the memory (not usable) and keeps on increasing at various visits to the page. I don't know how how to clear the items of the GridView when OnNavigationFrom(,) method is called. I am trying to use objGridView.Items.Clear() but it throws some HRXXXX exception.