How to use require option in directives - angularjs

Question

In documentation I can read next for the require option:
When a directive uses this option, $compile will throw an error
unless the specified controller is found. The ^ prefix means that this
directive searches for the controller on its parents (without the ^
prefix, the directive would look for the controller on just its own
element).
So I try to use it:
<div ng-sparkline></div>
app.directive('ngCity', function() {
return {
controller: function($scope) {}
}
});
app.directive('ngSparkline', function() {
return {
restrict: 'A',
require: '^ngCity',
scope: {},
template: '<div class="sparkline"><h4>Weather </h4></div>',
link: function(scope, iElement, iAttrs) {
// get weather details
}
}
});
But I have an error if my html have not ng-city attribute, so if I need controller of another directive - need to add exactly same attribute in html, but why (<div ng-sparkline ng-city="San Francisco"></div>)? And it looks on another directive's controller with this name (directive!!!) but not at controller with this name, is that true? Thanks. Just want to make it clear

Answer 1

With require you can get the controller of another (cooperating) directive. The controller in Angular is not semantically a function, but an object constructor, i.e. called essentially as var c = new Controller() (this is a simplification for the sake of clarity). Since the controller is an object, it can have properties and methods. By requiring the controller of another directive, you gain access to those properties/methods. Modifying your example to demonstrate:
app.directive('ngCity', function() {
return {
controller: function($scope) {
this.doSomething = function() {
...
};
}
}
});
app.directive('ngSparkline', function() {
return {
restrict: 'A',
require: '^ngCity',
scope: {},
template: '<div class="sparkline"><h4>Weather </h4></div>',
link: function(scope, iElement, iAttrs, ngCityController) {
// use the controller, e.g.
ngCityController.doSomething();
}
}
});
In your case, the city would be a property of the controller of the ngCity directive, exposed as a property. It will be read by the ngSparkline to know for which city the graph is about.

Answer 2

<b> added directives.js</b>
<code>
app.directive('ngSparkline', function () {
return {
restrict: 'A',
require: '^ngCity',
scope: {
ngCity: '#'
},
templateUrl: '/scripts/templates/tpl.html',
controller: ['$scope', '$http', function ($scope, $http) {
var url = "https://api.openweathermap.org/data/2.5/forecast/daily?mode=json&units=imperial&cnt=7&callback=JSON_CALLBACK&q=";
console.log(url + $scope.ngCity);
$scope.showTemp = function () {
$scope.getTemp($scope.ngCity);
};
$scope.getTemp = function (city) {
$http({
method: 'JSONP',
url: url + city
}).success(function(data) {
var weather = [];
angular.forEach(data.list, function(value){
weather.push(value);
});
$scope.weather = weather;
});
}
}],
link: function (scope, iElement, iAttrs, ctrl) {
scope.getTemp(iAttrs.ngCity);
scope.$watch('weather', function (newVal) {
if (newVal) {
var highs = [];
angular.forEach(scope.weather, function (value) {
highs.push(value.temp.max);
});
//chartGraph(iElement, highs, iAttrs);
}
});
}
}
}).directive('ngCity', function () {
return {
controller: function ($scope) {
//console.log("hello");
}
}
});
</code>
<b> and added tpl.htm</b>
<code>
<div class="sparkline">
<input type="text" data-ng-model="ngCity">
<button ng-click="showTemp()" class="btn1">Check {{ngCity}}</button>
<div style="color:#2743EF">{{weather}} ºC</div>
<div class="graph"></div>
</div>
</code>