public void CanUseCurrentValueWhenRecalculating()
{
var optionsViewModel = new OptionsViewModel
{
Options = new ObservableCollection<string>
{
"Item 1",
"Item 2",
"Item 3"
},
SelectedOption = "Item 1"
};
engine
.Assign(() => optionsViewModel.SelectedOption)
.From(currentValue => UnselectInvalidOption(currentValue, optionsViewModel.Options), ex => { });
// change a paramter of the formula, to check the formula triggers and use correct current value
optionsViewModel.Options = new ObservableCollection<string>
{
"Item 1",
"Item 2"
};
optionsViewModel.SelectedOption.ShouldBe("Item 1");
// again, change a paramter of the formula, to check the formula triggers and use correct current value
optionsViewModel.Options = new ObservableCollection<string>
{
"Item 2",
"Item 3"
};
optionsViewModel.SelectedOption.ShouldBe(null);
}
public void ChangingTargetPropertyShouldNotTriggerExpressionEvaluation()
{
var optionsViewModel = new OptionsViewModel();
engine
.Assign(() => optionsViewModel.SelectedOption)
.From(() => CountHowManyTimesCalled(optionsViewModel.Options), ex => { });
string dotFormat = engine.ToDotFormat("Foo");
Console.WriteLine(dotFormat);
// reset count to 0 (because of issue 1)
count = 0;
// change the target property
optionsViewModel.SelectedOption = "Item2";
// check that the formula was not evaluated
count.ShouldBe(0);
// Note: this seems to be caused by DepdendencyEngine.FindChangedNode returning the wrong node.
// this method is super confusing, spent some time on it and just can't understand the logic, I prefer to not touch it
}