我无法获得UIElement的ActualSize

Question

I have an Image control, generated in runtime. It renders correct size when displaying. But I can't get size of that element. Width and Height is NaN. ActualWidth and ActualHeight is always 0.0 and control never fires SizeChanged event.

I'm also generating TextBoxes in the runtime and I can't get size of them too.

The code that generates image is bellow.

ExtendedImage image = new ExtendedImage();
image.Name = "element" + item.Id;
if (item.Text.ToUpperInvariant().EndsWith(".GIF"))
{
    var gif = BookReader.Imaging.GIFDecoder.Decode(Application.GetResourceStream(new Uri("Files/Books/" + item.BookId + "/" + item.Text, UriKind.Relative)).Stream);
    image.Source = gif.Frames[0].Image;
}
else
{
    var img = new BitmapImage(new Uri("/Files/Books/" + item.BookId + "/" + item.Text, UriKind.Relative));
    image.Source = img;
}

image.SetValue(Canvas.LeftProperty, (double)item.LocationX);
image.SetValue(Canvas.TopProperty, (double)(Application.Current.Host.Content.ActualHeight - item.LocationY));

image.SizeChanged += (o, e) =>
{
    var sender = o as ExtendedImage;
    image.SetValue(UIElement.RenderTransformOriginProperty, new Point(0.5, 0.5));
};

image.InvalidateMeasure();

if (!item.Visible)
{
    image.Visibility = System.Windows.Visibility.Collapsed;
}

ContentPanel.Children.Add(image);

Answer 1

You can't access the size of the image before it's been rendered. And you can't render a item in a Canvas , without it having a explicit size.

So your problem is that you're attempting to get the size of the image before it's actually been rendered.

Answer 2

If the container of the Image has Height and Width , the image should have it as well. Try to put your Image into a Grid or StackPanel and set the size explicitly.