如何在AngularJS回调中设置变量？

var self = this;
self.variable = null;

$http.get('api/data').then(function(response) {
  self.variable = response.data;
});

app.controller('MyController', function($scope, $http) {
  $scope.variable = null;

  $http.get('api/data').then(function(response) {
    $scope.variable = response.data;
  });
});