Binding properties to DataTemplate

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 ?

Juan Carlos Rodriguez · Accepted Answer · 2018-04-20 13:36:02Z

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

answered Apr 20, 2018 at 13:36

Juan Carlos Rodriguez

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3 Comments

Valentin Marie Over a year ago

So... I added the RelativeSource and Path => it was better but not working at 100% (The Get was reached just one time (at the begining), but not after the update). Now, I added Inherits GalaSoft.MvvmLight.ViewModelBase to my class (and RaisePropertyChanged by property), and, Grid of my DataTemplate has DataContext="{Binding DataContext, RelativeSource={RelativeSource AncestorType=ContentControl}}", and the binding targeted only the property name (Visibility or Message). Thank you very much !

Juan Carlos Rodriguez Over a year ago

That’s why I asked you if you had INotifyPropertyChanged in my other answer. You should raise it every time it changes. Galas I helped you :) pls upvote my answer so you help me too:)

Valentin Marie Over a year ago

After you'r first question, I tried to Implements INotifyPropertyChanged to my class, but it was not working. I think this is because the RelativeSource was missing. I have already upvoted your answer, but because I have only 3 of Reputation, it is not yet accounting (15 is needed) :/

aydjay · Accepted Answer · 2018-04-20 10:08:39Z

0

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.

answered Apr 20, 2018 at 10:08

aydjay

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4 Comments

Valentin Marie Over a year ago

You are saying that I should to use 2 properties instead of my object ? And so with the RaisePropertyChanged, the binding will works ?

aydjay Over a year ago

Your datacontext should be the object which holds your data. The data that you want to display on that object needs to be a public property with the gets sets notifying.

Valentin Marie Over a year ago

I tried to make an inheritance to my class but the binding not working again. I tried another way : 2 properties in my VM (Visibility and Message), and bind the DataTemplate components to these 2 properties. It's not working. But If I do that directly in my UserControl, it's OK. So the problem is when i'm using the Template, but I don't know why.

aydjay Over a year ago

Check your output window to make sure you don't have any binding errors. Post how you are binding your UI to you object.

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