Not able to view preview

Hello @vivekse ,

there are 2 question: 

Why do you need the call apply call here. So remember the defintion:

"$scope.$apply() function takes a function as parameter which is executed, and after that $scope.$digest() is called
internally. That makes it easier for you to make sure that all watches are checked, and thus all data bindings refreshed.
Here is an $apply() example:
$scope.$apply(function() {
$scope.data.myVar = "Another value";
});
The function passed to the $apply() function as parameter will change the value of $scope.data.myVar. When the
function exits AngularJS will call the $scope.$digest() function so all watches are checked for changes in the watched
values."

============

If you want to update you can use any function call and then call $digest.

think calling the $apply before the studio is initialized will always lead to error.

This will lead  to the second problem that you Preview is not displayed properly. So, I believe when you open the chrome  console window (Strg-Shift-I) you will see some error like ...Error: [$rootScope:inprog]...

If you use e.g. the following code it should work as intented:

var ydelta = 0.1;
////////////////
$scope.$on('$ionicView.afterEnter', function() {

$scope.$apply(function(){
 console.info("$scope.$apply funciton");
 if(isNaN(parseFloat($scope.app.params.ypos))) $scope.app.params.ypos='0';
 console.log(" ydelta=", ydelta)
 $scope.app.params.ypos = Math.max(0.045, parseFloat($scope.app.params.ypos)+ydelta ); 
})
$scope.goDown = function() { ydelta = -0.005; }

So tested and it worked. I  also binded the parameter ypos to a label widget and it was updated properly :