how to measure UIElement created from hierachical datatemplate - silverlight

Question

folks, I am about to print a hierachical data from Silverlight 5. I use a resource dictionary to define the layout of the data. The main xaml segments like this:
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:MSCE.SL.ArchievementAssessment"
xmlns:stat="clr-namespace:MSCE.SL.ArchievementAssessment.Statistics">
<DataTemplate DataType="stat:Level1">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto"/>
<ColumnDefinition>
</Grid.ColumnDefinitions>
<TextBlock Text="{Binding Name}" VerticalAlignment="Center"/>
<ItemsControl Grid.Column="1" ItemsSource="{Binding Children}"/>
</Grid>
</DataTemplate>
<DataTemplate DataType="stat:Level2">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto"/>
<ColumnDefinition>
</Grid.ColumnDefinitions>
<TextBlock Text="{Binding Name}" VerticalAlignment="Center"/>
<ItemsControl Grid.Column="1" ItemsSource="{Binding Children}"/>
</Grid>
</DataTemplate>
<DataTemplate x:Key="Level3ItemTemplate">
....
</DataTemplate>
<DataTemplate DataType="stat:Level3">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto"/>
<ColumnDefinition>
</Grid.ColumnDefinitions>
<TextBlock Text="{Binding Name}" VerticalAlignment="Center"/>
<ListBox Grid.Column="1" ItemsSource="{Binding Children}"
ItemTemplate="{StaticResource Level3ItemTemplate}"/>
</Grid>
</DataTemplate>
</ResourceDictionary>
then I use those templates in printing code as follow:
void Print(object para)
{
PrintDocument pd = new PrintDocument();
List<FrameworkElement> pages = null;
int pageIndex = 0;
pd.PrintPage += (s, e) =>
{
if (pages == null)
{
pages = CreatePages(e.PrintableArea);
}
e.PageVisual = pages[pageIndex] ;
pageIndex++;
e.HasMorePages = pageIndex < pages.Count;
};
pd.Print("statistics");
}
List<FrameworkElement> CreatePages(Size printableArea)
{
// create result pages' container
List<FrameworkElement> pages=new List<FrameworkElement>();
// get resources for printing
IEnumerable<Level1> data=...// detail ignored, get data from ViewModel
ResourceDictionary res=... // detail ignored, get data template from assembly
// create page root visual and
// merge printing templates' resource into root's resource dictionary
StackPanel root=new StackPanel();
root.ResourceDictionary.MergedDictionaries.Add(res);
// fetch data template of data Level1
var level1Template=root.Resources[new DataTemplateKey(typeof(Level1))] as DataTemplate;
// trace height of available space
double availableContentHeight=printableArea.Height;
foreach(var lvl1 in data)
{
// create UI of Level1 using template
var ui=level1Template.LoadContent() as FrameworkElement;
ui.DataContext = data;
ui.OnApplyTemplate();
// measure the size requirement of this Level1's UI
ui.Measure(printableArea);
// if available space is not enough, add the last page to pages container
// and create a new page to contain new created Level1 UI
if(ui.DesireSize.Height>availableContentHeight)
{
pages.Add(root);
root=new StackPanel();
availableContentHeight=printableArea.Height;
}
root.Children.Add(ui);
availableContentHeight-=ui.DesiredSize.Height;
}
pages.Add(root);
return pages;
}
The problem occurs at Measuring. It should contain about three pages. But the sum of the heights of all Level1 UIs based on Measure results occupy only half a page. So the printer prints always only one page and cuts many content down. I think that the Measure method for Level1 UI returns only the height of his title(TextBlock Text="{Binding Name}"), it doesn't include the space requirements of level1's children and certainly the space requirements of level2's children.
At the begining, I didn't put the statement ui.OnApplyTemplate(). After the problem occured, I thought that this might preload all children content and I could get right measuring result. But in the fact it changes nothing.
Now, my thought is, either preloading the whole visual tree for data Level1 before adding it to PageVisual of PringPageEventArgs to get right measuring result, or write a hierachical measuring method to measure Level1 UI from the bottom (level3's children) to top.
Because that my actual data templates are more complicated than the above ones, the second method is time comsumed and is prone to introduce bugs. So I hope someone to teach me how to accomplish the first road or direct me to a clear solution.

Answer 1

Well, after some days, I had to handle the measuring problem with proximate algorithm. I assume that every detailed level3 row occupys only one row and then measure height of each row and sum all height values up. Without accruate measuring, not perfect, but It can cope with the case.