Button doesn't update with new inputDate from Ionic Date Picker - angularjs

Question

I need a date picker for my Ionic app. I am trying to use this one as it seems popular:
https://github.com/rajeshwarpatlolla/ionic-datepicker
I have tried to follow the tutorial, and it works well, but the date button doesn't update based on the date selection. How can I make it update?
My code is below.
This is my controller:
app.controller('EnterDatapointCtrl', function($scope, $state) {
$scope.datepickerObject = {
titleLabel: 'Title', //Optional
inputDate: new Date(), //Optional
callback: function (val) { //Mandatory
datePickerCallback(val);
}
};
var datePickerCallback = function (val) {
if (typeof(val) === 'undefined') {
console.log('No date selected');
} else {
console.log('Selected date is : ', val)
}
};
});
This is my template:
<ion-view view-title="New Sales">
<ion-content class="padding">
<ionic-datepicker input-obj="datepickerObject">
<button class="button button-block button-positive"> {{datepickerObject.inputDate | date:'dd - MMMM - yyyy'}}</button>
</ionic-datepicker>
<div class="list list-inset">
<label class="item item-input">
<input type="text" placeholder="Amount" ng-model="data.amount">
</label>
</div>
<button class="button button-block button-stable" ng-click="save()">Save</button>
</ion-content>
</ion-view>

Answer 1

I added a line to the callback. I didn't understand that I was supposed to modify the callback function.
$scope.datepickerObject.inputDate = val;
app.controller('EnterDatapointCtrl', function($scope, $state) {
$scope.datepickerObject = {
titleLabel: 'Title', //Optional
inputDate: new Date(), //Optional
callback: function (val) { //Mandatory
datePickerCallback(val);
}
};
var datePickerCallback = function (val) {
if (typeof(val) === 'undefined') {
console.log('No date selected');
} else {
console.log('Selected date is : ', val)
$scope.datepickerObject.inputDate = val;
}
};
$scope.save = function() {
$state.go('confirm-datapoint');
};
});