Firebase Array Fetches Not Loading on Page Load

问题

// Movements Controller
app.controller("MovementsCtrl", ["$scope", "$rootScope", "$filter", "$timeout", "$route", function($scope, $rootScope, $filter, $timeout, $route) {
  $rootScope.pageName = "Movements";

  var date = new Date();
  var currentDate = $filter('date')(new Date(), 'MM/dd/yyyy');

  $scope.labels = [];
  $scope.data = [];
  $scope.recordsArray = []; // Converts records object into an array.
  console.log($scope.recordsArray);

  firebase.auth().onAuthStateChanged(function(user) {
    if (user) {
      $rootScope.userID = user.uid;

      // Run query to pull user records.
      $timeout(function() {
        var userID = $rootScope.userID;
        var query = firebase.database().ref('/users/' + userID +'/movements/').orderByChild('created');

        query.on("value", function(snapshot) {
            $scope.records = snapshot.val();

              angular.forEach($scope.records, function(element) {
                $scope.recordsArray.push(element);
                $scope.labels.push(element.name);
                $scope.data.push(element.weight);
              });
        });
      });
    } else {
      console.log("not signed in");
    }
  });

  $scope.addRecord = function() {
    console.log("Pushed");
    var recordID = database.ref().push().key;
    var userID = $rootScope.userID;

    database.ref('users/' + userID + '/movements/' + recordID).set({
      user: userID,
      name: "Front Squat",
      sets: 5,
      reps: 5,
      weight: 350,
      created: currentDate
    });
    $route.reload();
  }
}]);

For some reason my page loads before the arrays in my JS load, rendering an empty page. I've tried wrapping everything in an init() function and loading that, but still the same issue. Can anyone help me figure out how to pre-load my JS arrays beforehand or is there another solution?

Thanks.

回答1:

some reason my page loads before the arrays

The functions provided as arguments to the Firebase methods are held by the Firebase API until data arrives from the server. Those functions are executed asynchronously. This means they are executed after the enclosing functions complete.

Changes to scope that occur asynchronously outside the AngularJS framework and its digest cycle will not trigger changes to the DOM. One technique to bring events into the AngularJS framework is to convert the ES6 promises to $q service promises:

  firebase.auth().onAuthStateChanged(function(user) {
    if (user) {
      $rootScope.userID = user.uid;

      // Run query to pull user records.
      //$timeout(function() {
        var userID = $rootScope.userID;
        var query = firebase.database().ref('/users/' + userID +'/movements/').orderByChild('created');

        //USE $q.when 
        $q.when(query.once("value")).then(function(value) {
            $scope.records = value;

              angular.forEach($scope.records, function(element) {
                $scope.recordsArray.push(element);
                $scope.labels.push(element.name);
                $scope.data.push(element.weight);
              });
        });
      //});
    } else {
      console.log("not signed in");
    }
  });

Use $q Service promises that are properly integrated with the AngularJS framework and its digest cycle.

$q.when

Wraps an object that might be a value or a (3rd party) then-able promise into a $q promise. This is useful when you are dealing with an object that might or might not be a promise, or if the promise comes from a source that can't be trusted.

-- AngularJS $q Service API Reference - $q.when

来源：https://stackoverflow.com/questions/42911751/firebase-array-fetches-not-loading-on-page-load