Applying binding after the Windows's Initialization?

Question

I searched a lot to find a solution to get the ActualWidth of an image in a ViewModel class. The solution is [Link]. I am trying to change the
width/height of the Image at runtime using a slider. When the image is inserted, I want to get the actualHeight of the Image and increase/decrease the size according to slider in percentage so that it'll stay in correct aspect ratio. As I have set the Image
width/height to bind to the property in the VM and until the image is loaded I won't know the image size, it sets it to 0. Henceforth the percentage increase of 0  = 0! 
Here is the code:
<Image x:Name="GraphImage" Source="{Binding ImageSrc,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" Width="{Binding ImageWidth,UpdateSourceTrigger=PropertyChanged}" Height="{Binding ImageHeight,UpdateSourceTrigger=PropertyChanged}">
<pb:PushBindingManager.PushBindings>
<pb:PushBinding TargetProperty="ActualHeight" Path="Height"/>
<pb:PushBinding TargetProperty="ActualWidth" Path="Width"/>
</pb:PushBindingManager.PushBindings> </Image>
public double ZoomValue
get { return _ZoomValue; }
set
_ZoomValue = value;
ImageHeight = (_ZoomValue / 100 * Height) + Height;
ImageWidth = (_ZoomValue / 100 * Width) + Width;
NotifyPropertyChanged();

Answer 1

>>I have bind the Width and Height of Image to the VM properties, before initializing the image, its width and height are set to 0. Thereafter, the ActualWidth and ActualHeight are set to 0 also.
Of course the ActualWidth and ActualHeight are 0 if you have set the height and width properties to 0...you can specify default values in the view model class if you want the image to have a default size before the sliders have been touched, e.g:
private int _imageWidth = 50; //default width
public int ImageWidth
get { return _imageWidth; }
set { _imageWidth = value; }
>>I need to somehow send the ActualWidth before setting its Width.
Why? The ActualWidth will always 0 before the Width has been set anyway. If you want to know the value of the ActualWidth property whenever the Width property changes, you could handle the SizeChanged event for the Image and send a message to the VM in the
event handler:
<Image x:Name="GraphImage" Source="..."
SizeChanged="GraphImage_SizeChanged"
Width="{Binding ImageWidth,UpdateSourceTrigger=PropertyChanged}"
/>
private void GraphImage_SizeChanged(object sender, SizeChangedEventArgs e)
Image image = sender as Image;
double actualWidth = image.ActualWidth;
//send to VM using messenger....
This event is invoked whenever the size changes.
The other option is to keep a loose reference to the view (the view implements an interface with a "GetActualWidth" method which is implemented to return the ActualWidth of the Image element) in the view model class and get the ActualWidth in the
setter of the ImageWidth source property:
public int ImageWidth
get { return _imageWidth; }
set
_imageWidth = value;
double actualWidth = _viewReference.GetActualWidth();
//do whatever...
You pass the view reference to the view model class when you create it:
this.DataContext = new ViewModel(this);
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