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Revision as of 08:16, 15 October 2012 by hamishwillee (Talk | contribs)

How to debug data binding problems on Windows Phone

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Often XAML elements with data binding show no data during development. This article shows one method how to find the source of this problem.

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Article Metadata
CompatibilityArticle
Created: influencer (12 Oct 2012)
Last edited: hamishwillee (15 Oct 2012)

Contents

Introduction

If you use data binding in your Windows Phone application, during development you'll come to the point where you have linked everything together but data doesn't display correctly in your control.

Solution

What can you do? You can use an IValueConverter and set a breakpoint there. This way you can see what data arrives at your element and check the available properties.

Say you have a ListBox like this:

         <ListBox x:Name="MainListBox" Margin="0,0,-12,0" ItemsSource="{Binding Items}" SelectionChanged="MainListBox_SelectionChanged">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Margin="0,0,0,17" Width="432" Height="78">
<TextBlock Text="{Binding LineOne}" TextWrapping="Wrap" Style="{StaticResource PhoneTextExtraLargeStyle}"/>
<TextBlock Text="{Binding LineTwo}" TextWrapping="Wrap" Margin="12,-6,12,0" Style="{StaticResource PhoneTextSubtleStyle}"/>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>

You can add a converter that gets called when the data from the binding source arrives and before it gets delivered to the control. Here we have one condition when this debugging technique can't help: if the binding fails beforehand, the converter doesn't get called.

To implement the converter you have to derive a class from IValueConverter and implement it's methods:

   public class DatabindingDebugConverter : IValueConverter
{
public object Convert(object value, Type targetType,
object parameter, string language)
{
return value;
}
 
public object ConvertBack(object value, Type targetType,
object parameter, string language)
{
return value;
}
}

Then you have to declare the converter as a static resource in your page's xaml:

   <phone:PhoneApplicationPage.Resources>
<local:DataBindingDebugConverter x:Key="DatabindingDebugConverter"/>
</phone:PhoneApplicationPage.Resources>

assuming you have declared the local namespace

    xmlns:local="clr-namespace:EncryptionSample"

in the page tag and call it in the data binding statement:

      <TextBlock Text="{Binding LineOne, Converter={StaticResource DataBindingDebugConverter}}" TextWrapping="Wrap" Style="{StaticResource PhoneTextExtraLargeStyle}"/>

Next you set a breakpoint in the Convert method and voilà, you can see the values that arrive from binding, if any.

Sample code

A running sample is contained in the sample code for the How to encrypt your application data in Windows Phone article, please refer there.

Version Hint

Windows Phone: [[Category:Windows Phone]]
[[Category:Windows Phone 7.5]]
[[Category:Windows Phone 8]]

Nokia Asha: [[Category:Nokia Asha]]
[[Category:Nokia Asha Platform 1.0]]

Series 40: [[Category:Series 40]]
[[Category:Series 40 1st Edition]] [[Category:Series 40 2nd Edition]]
[[Category:Series 40 3rd Edition (initial release)]] [[Category:Series 40 3rd Edition FP1]] [[Category:Series 40 3rd Edition FP2]]
[[Category:Series 40 5th Edition (initial release)]] [[Category:Series 40 5th Edition FP1]]
[[Category:Series 40 6th Edition (initial release)]] [[Category:Series 40 6th Edition FP1]] [[Category:Series 40 Developer Platform 1.0]] [[Category:Series 40 Developer Platform 1.1]] [[Category:Series 40 Developer Platform 2.0]]

Symbian: [[Category:Symbian]]
[[Category:S60 1st Edition]] [[Category:S60 2nd Edition (initial release)]] [[Category:S60 2nd Edition FP1]] [[Category:S60 2nd Edition FP2]] [[Category:S60 2nd Edition FP3]]
[[Category:S60 3rd Edition (initial release)]] [[Category:S60 3rd Edition FP1]] [[Category:S60 3rd Edition FP2]]
[[Category:S60 5th Edition]]
[[Category:Symbian^3]] [[Category:Symbian Anna]] [[Category:Nokia Belle]]

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