Silverlight - What does my datacontext/binding path need to be here? - wpf

Question

I've been working a bit with an image editor in Silverlight for the past week or so. It's my first encounter with it and I still haven't fully gotten my head around data bindings and datacontext or mvvm. I have a rotation method and I want to be able to pass the angle value from a text box on my MainPage.xaml to the method.I have an initial value set of 90 and my function rotates the image 90 degrees when I click it. The textbox is empty at runtime and also is clearly not updating my rotation angle.
MainPage.xaml
<Grid DataContext="{Binding Path=Project}" Height="70" Name="grid1" Width="200">
<Grid.RowDefinitions>
<RowDefinition Height="35" />
<RowDefinition Height="35" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="84*" />
<ColumnDefinition Width="57*" />
<ColumnDefinition Width="59*" />
</Grid.ColumnDefinitions>
<Button Command="{Binding Path=RotateCWElementCommand}"
Height="30" Name="btnRotCW" Width="30" Grid.Column="2" Margin="15,0,14,5" Grid.Row="1">
<Image Source="../Assets/Images/Icons/object-rotate-right.png" Grid.Column="1"
Grid.Row="4" Height="20" HorizontalAlignment="Left" Name="image1" Stretch="Fill" VerticalAlignment="Top" Width="20" />
</Button>
<TextBlock FontWeight="Bold" HorizontalAlignment="Left" Margin="10,10,0,8" Text="Rotate" VerticalAlignment="Center" />
<TextBlock FontWeight="Bold" HorizontalAlignment="Left" Margin="34,9,0,10" Text="Angle:" VerticalAlignment="Center" Grid.Row="1" />
<TextBox Text="{Binding Path=RotateElement.Angle, Mode=TwoWay}" Height="24" Name="textBox1" Width="52" Grid.Column="1" Margin="0,6,5,5" Grid.Row="1" />
</Grid>
(Relevant code from)
Project.cs-
namespace ImageEditor.Client.BLL
{
public class Project : INotifyPropertyChanged
{
#region Properties
private RotateTransform rotateElement;
public RotateTransform RotateElement
{
get { return rotateElement; }
set
{
rotateElement = value;
NotifyPropertyChanged("RotateElement");
}
}
#endregion
#region Methods
private void RotateCWElement(object param)
{
FrameworkElement element = this.SelectedElement;
RotateTransform RotateElement = new RotateTransform();
RotateElement.Angle = 90;
RotateElement.CenterX = element.ActualWidth * 0.5;
RotateElement.CenterY = element.ActualHeight * 0.5;
element.RenderTransform = RotateElement;
}
What am I doing wrong here? Is it my datacontext or my binding path that is the problem? What should they be? Formatting is a little off sorry

Answer 1

the UI does not know that a property in your object has changed, since you only notify when your object changes, but not the properties in it:
private void RotateCWElement(object param)
{
FrameworkElement element = this.SelectedElement;
if (this.RotateElement == null) this.RotateElement = new RotateTransform();
RotateElement.Angle = 90;
RotateElement.CenterX = element.ActualWidth * 0.5;
RotateElement.CenterY = element.ActualHeight * 0.5;
element.RenderTransform = RotateElement;
//tell the UI that this property has changed
NotifyPropertyChanged("RotateElement");
}