In the last post I described the first attempt at binding priorites in Perspex.
To see the problem with this simple system consider the following example:
var textBox = new TextBox();
textBox.Bind(TextBox.TextProperty, viewModel.WhenAnyValue(x => Text));
textBox.GetObservable(TextBox.TextProperty).Subscribe(x => viewModel.Text = x);This creates a two-way binding between the TextBox.Text property and the
viewModel.Text property. But there’s a problem. With the system described in
part 1, local values are stored as bindings, as the PriorityValue is just
a linked list of bindings.
Which means that a user typing into the TextBox overrides the binding setup above. So a binding would fire only once after user interaction and remain dormant from then on.
Clearly this isn’t desirable behavior.
The solution was that for each priority level, you need a “local value” : a
value set using PerspexObject.SetValue that takes affect only until the next
time a binding of the same priority fires.
And this is the story of how PriorityValue became a collection of
PriortyLevels.
However, this isn’t the end of the story…