absolute position(x,y) of ListBoxItem - Binding self , IValueConverter and TransformToVisual - is it possible?

Tadek

15y5.5k

Hi,

I'm trying something like this:

....

....

and

class Position : IValueConverter
{

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
GeneralTransform generalTransform = value.TransformToVisual(null); // here I get error
Point point = generalTransform.Transform(new Point());

return "X="+Point.X+"Y="+Point.Y;
}
....

and the result is following error: 'object' does not contain a definition for 'TransformToVisual' and no extension method 'TransformToVisual' accepting a first argument of type 'object' could be found

Any ideas how to solve this, or maybe some one know different approach to get absolute position of listbox elements?

Regards,
Tadek.

4 Replies

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Sam Hobbs15y ago
Accepted answer
"value" is an object so it does not have a TransformToVisual method, just as the compiler is saying. You just need to cast "value" back to the type that it really is. Better than that, you should use the correct type in the parameter specification for "value". Is there some reason you cannot do either of those?
0
Tadek15y ago
nope it doesn't matter. (I've ripped this part)
converter works same with Point(0,0) and Point()
but Im binding to ancestor grid rather than textblock itself (binding self always crashed regardless of converter contents).

It works somehow:
Blend have sometimes problems with it ("cannot resolve AbsolutePosition resource") , its ok in VS.
In design view it shows positions in Internal.designer
on run shows correct values.

It's not a perfect and still need to do some refreshing.
0
Sam Hobbs15y ago
I am not sure I understand. You create a new Point with (0,0) and then return it's X and Y so of course X and Y are always zero.
0
Tadek15y ago
thx I've changed this (noobizm - I admit it) and added visual root finding function

and now my converter class looks like this

class AbsolutePosition : IValueConverter
{
#region IValueConverter Members

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
var myVisualRoot = FindVisualTreeRoot(value as DependencyObject);
GeneralTransform generalTransform = (myVisualRoot as Visual).TransformToVisual(value as System.Windows.Controls.TextBlock);
Point point = generalTransform.Transform(new Point(0,0));

return "X:" + point.X.ToString() + "Y:" + point.Y.ToString() + "root name:" + myVisualRoot.ToString();

}

public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}

#endregion

DependencyObject FindVisualTreeRoot(DependencyObject initial)
{
DependencyObject current = initial;
DependencyObject result = initial;

while (current != null)
{
result = current;
if (current is Visual || current is Visual3D)
{
current = VisualTreeHelper.GetParent(current);
}
else
{
current = LogicalTreeHelper.GetParent(current);
}
}

return result;
}
}

...and the results are x:0 y:0 for every item,
courious thing - when I'll make some irrevelant change in converter resource link code so design view will reload - it shows probable results,

but on the run all are zeros.

0