Uwp binding control getting Width in viewmodel

1
votes

I'm currenly working on a UWP app using the map control. I'm doing this using mvvm (no framework). In my viewmodel I do a calculation on how many meters you actually see (width). I do this by calculating how many meters a pixel represent, and then I multiply this by the width of the control. And there is where the problem is. In WPF you had a mode OneWayToSource, which would set the source value and not change the target value. But this is missing in UWP. If I use a binding, I must set the width in my viewmodel. And this is something I don't want. I just want to get the width of the map. And that is not the only problem. I don't actually need the width ,because this gives NaN, what I need is the ActualWidth. But this is a backing field and you can't bind to this from xaml.

Is there a solution for this while still preserving the mvvm pattern?

1
mvvmuwp

1 Answers

2
votes

ActualWidth and ActualHeight should never be the source or target of a binding. They simply don't work in that situation. You'll need to obtain the size of the element by listening to its SizeChanged event. There are 3 ways you can do this:

  1. x:Bind the SizeChanged event to a method in your view model.
  2. Create an attached property which syncs its value to the size of the element by listening to SizeChanged events. You can then TwoWay bind to this property.
  3. Write a behavior which does basically the same thing as 2.