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Revision as of 18:53, 12 October 2012 by influencer (Talk | contribs)

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How to debug data binding problems on Windows Phone

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Created: influencer (12 Oct 2012)
Last edited: influencer (12 Oct 2012)

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 in your control or the wrong data appears.

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 earlier, the converter doesn't get calledt

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.

A sample project is in the works, please call again later...



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