Binding properties to DataTemplate - wpf

Question

I'm using a DataTemplate which is inside a ResourceDictionary file.
<DataTemplate x:Key="AlertWarningMessage">
<Grid>
<Border Visibility="{Binding DataContext.Visibility}" Background="{StaticResource ResourceKey=AlertWarningMessageBackground}" HorizontalAlignment="Stretch" Height="30">
<WrapPanel Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Center">
<TextBlock Text="WARNING !" FontWeight="Bold" Foreground="{StaticResource ResourceKey=AlertWarningMessageForeground}" FontSize="13"/>
<TextBlock Text="{Binding DataContext.Message}" Foreground="{StaticResource ResourceKey=AlertWarningMessageForeground}" Margin="5,0,0,0"/>
</WrapPanel>
</Border>
</Grid>
</DataTemplate>
I merge this dictionnary in my UserControl, and i'm using this template like this :
<ContentControl ContentTemplate="{StaticResource AlertWarningMessage}" Grid.Row="2" Margin="0,2,0,0" DataContext="{Binding AlertSummary, UpdateSourceTrigger=PropertyChanged}" />
In my VM, i'm using a class which have 2 properties :
Public Class AlertInfos
Public Property Visibility As Visibility
Public Property Message As String
Public Sub New(p_visibility As Visibility, p_msg As String)
Me.Visibility = p_visibility
Me.Message = p_msg
End Sub
End Class
Property VM as my class :
Private _alertSummary As AlertInfos
Public Property AlertSummary() As AlertInfos
Get
Return _alertSummary
End Get
Set(ByVal value As AlertInfos)
_alertSummary = value
RaisePropertyChanged("AlertSummary")
End Set
End Property
Properties of this object are set to Collapsed and String.Empty
Next, I change the values of this object, like this :
Public Sub ShowAlert()
Me.AlertSummary.Message = "Test"
Me.AlertSummary.Visibility = Visibility.Visible
'Me.StartTimerAlert()
RaisePropertyChanged("AlertSummary")
End Sub
But it's not working. There are 2 problems :
At the begining, when the Visibility is set to Collapsed, the Border is visible.
When I change the Message property, it is not visually updated.
I think there is a problem with my Binding, but I don't know where. I tried differents things, but there is always these problems.
Furthermore, I had bind the property directly in a TextBlock below the ContentControl, and the Binding working find.
Do you have any idea ?

Answer 1

You should change your data template to this:
<DataTemplate x:Key="AlertWarningMessage">
<Grid>
<Border Visibility="{Binding RelativeSource={RelativeSource AncestorType=ContentControl}, Path=DataContext.Visibility}" Background="AliceBlue" HorizontalAlignment="Stretch" Height="30">
<WrapPanel Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Center">
<TextBlock Text="WARNING !" FontWeight="Bold" Foreground="Red" FontSize="13"/>
<TextBlock Text="{Binding RelativeSource={RelativeSource AncestorType=ContentControl}, Path=DataContext.Message}" Foreground="Red" Margin="5,0,0,0"/>
</WrapPanel>
</Border>
</Grid>
</DataTemplate>
And your AlertInfos to this (it's on C# so try to translate it to VB)
public class AlertInfos
{
private string message;
public string Message
{
get
{
return this.message;
}
set
{
if (this.message != value)
{
this.message = value;
}
}
}
private Visibility visibility;
public Visibility Visibility
{
get
{
return this.visibility;
}
set
{
if (this.visibility != value)
{
this.visibility = value;
}
}
}
}
It should work, at least it's working on my PC

Answer 2

I'm not familiar with VB but Message needs to RaisePropertyChanged
Visibilities are commonly bound too bools which also RaisePropertyChanged - these then use a BooleanToVisibilityConverter
Make sure your properties are public - have private backing variables and RaisePropertyChanged.
private bool _isSomethingVisibile;
public bool IsSomethingVisibile
{
get { return _isSomethingVisibile; }
set
{
_isSomethingVisibile = value;
RaisePropertyChanged();
}
}
You don't need to preface your bindings with "DataContext" that is implied.