How to Converting a List of DateTime into Strings ?

The code block inside list.map is never executed.

This is because list.map produces a lazy transformation of the list. The transformation function is executed only when elements are requested from it.

You probably want to use:

var dates = list.map((DateTime time) {
      var dateRange = DateFormat("MM-dd-yy").format(time);
      return dateRange;
});
print(dates);

In the code above, it is the print function that forces the transformation to run.

Alternatively, you can transform the result of the list.map to a list using

var datesList = dates.toList();

Again, this forces eager evaluation of the map transformation.