How do you get the REAL position of objects in silverlight?

How do you get the REAL position of objects in silverlight?

I have a header image centered on the screen. When I make the browser window smaller, obviously, the header's left side goes off the screen. Finding out the actual p开发者_如何学JAVAosition is good to know if you want to position objects on top of the image.

I capture the Content_Resized and I run a little test:

        if (App.Current.Host.Content.ActualWidth > header.Width)
        {
            TEST = Canvas.GetLeft(header);
        }
        else
        {
            TEST = Canvas.GetLeft(header);

        }

TEST always returns zero.

EDIT: header sits on a grid instead of a canvas. "Well, there is your problem..." So a better question might be this. How would I get the margins of an image sitting on a grid?

I probably should just answer the question but how to find the position of an element relative to another is probably something that has been answered before (by myself and others) here and elsewhere on the tinternet.

However if your goal is to place an item over an image then place the image in a Grid and then add the item as child of the Grid. That way you assign the relative position over the image as the margin of the item and let Silverlight's layout system do the rest.

As a general rule if you feel that you need to write code to move stuff about when the size of things change then unless you are writing a custom panel or something you're probably not using Silverlight layout system properly.

Edit:

Try this experiment:-

 <Grid x:Name="LayoutRoot">
    <Grid x:Name="headerContainer" Margin="50, 60, 0, 0" HorizontalAlignment="Left" VerticalAlignment="Top">
        <Image Source="YourLargeImage" />
        <Image Source="YourSmallerImage" HorizontalAlignment="Center" VerticalAlignment="Top" />
    </Grid>
 </Grid>

Now try changing the inner grid's Margin to move its position around the screen. Note the smaller image always remains at the top center of the large image.

I got it working.

First of all, these images are on a grid, not a canvas. But switching the grid to a canvas caused lots of other problems one of which is that I could not have the header image centered like before.

The solution was to change the margin of the smaller image sitting on top of the larger header image when the content resized like this:

blankbarimage.Margin  = new Thickness((App.Current.Host.Content.ActualWidth - header.Width) / 2, 0, 0, 0);

and, by the way, you create a content resized method like this:

App.Current.Host.Content.Resized += new EventHandler(Content_Resized);

So, to answer my own question, the way you get the REAL position of object in silverlight is (if they are on a grid) by looking at their margin settings.