如何在Firebase中使用Ng-if-HowtouseanNg-ifwithFirebase

2  

I suggest to use the controllerAs syntax to ensure correct scope access and control.

我建议使用controllerAs语法来确保正确的范围访问和控制。

HTML:

HTML：

  

    
Parent is allowed
    
Children are allowed
    
Children are allowed
  
  Toggle Children

JS

JS

var app = angular.module('plunker', []);

app.controller('MainCtrl', function($scope) {
  var allowParent_ = true;
  var allowChildren_ = false;
  this.toggle = function() {
    allowChildren_ = !allowChildren_;
  }
  this.showParent = function(){
    return allowParent_;
  }

  this.showChildren = function() {
    return allowChildren_;
  }
});

2  

Promises returned by the firebase API are not integrated with the AngularJS framework.

firebase API返回的Promise未与AngularJS框架集成。

Use $q.when to create an AngularJS promise from a firebase promise:

使用$ q.when从firebase承诺创建AngularJS承诺：

var basePromise = firebase.database().ref('events/'+$r.selfID).once("value");
$q.when(basePromise).then(function(snapshot)
    {
       //.then block code   
    });

AngularJS modifies the normal Javascript flow by providing its own event processing loop. This splits the Javascript into classical and AngularJS execution context. Only operations which are applied in the AngularJS execution context will benefit from AngularJS data-binding, exception handling, property watching, etc.

AngularJS通过提供自己的事件处理循环来修改正常的Javascript流。这将Javascript拆分为经典和AngularJS执行上下文。只有在AngularJS执行上下文中应用的操作才会受益于AngularJS数据绑定，异常处理，属性监视等。

The firebase promise needs to be converted to an AngularJS promise to bring the event into the AngularJS execution context.

需要将firebase promise转换为AngularJS promise以将事件引入AngularJS执行上下文。

Save the returned value and log it.

保存返回的值并记录它。

$scope.set = function($r) {
    var value = set($r);
    console.log(value);
    return value;
}); 

//BUGGY function
function set($r)
{
    firebase.database().ref('events/'+$r.selfID).once("value").then(function(snapshot)
    {   
        var nbPerson = snapshot.val().nbPerson;
        var varPerson = snapshot.val().varPerson;

        //console.log("nbPerson :", nbPerson);
        //console.log("varPerson", varPerson);

        if(nbPerson === varPerson)
        {
            //console.log("true");
            return true;
        }
        else
        {
            //console.log("false");
            return false;
        }
    });
};

By using this simple debugging technique, you will quickly understand the problem.

通过使用这种简单的调试技术，您将很快了解问题。

the result of my set() function is unreachable... :( Is my new function (Edit 3), correct ?

我的set（）函数的结果是无法访问... :(是我的新功能（编辑3），对吗？

The return statements inside .then blocks do not return values to the parent function. The code inside .then blocks execute asynchronously after the parent function completes.

.then块内的return语句不会将值返回给父函数。 .then块内的代码在父函数完成后异步执行。

Javascript is single-threaded. Functions complete immediately. They can not return values created in .then blocks. They can only return values that are produced immediately and synchronously or they can return pending promises that later asynchronously resolve to some value.

Javascript是单线程的。功能立即完成。它们无法返回.then块中创建的值。它们只能返回立即和同步生成的值，或者它们可以返回挂起的promise，这些promise将在以后异步解析为某个值。

console.log("Part1");
console.log("Part2");
var promise = $http.get(url);
promise.then(function successHandler(response){
    console.log("Part3");
});
console.log("Part4");

The console log for "Part4" doesn't have to wait for the data to come back from the server. It executes immediately after the XHR starts. The console log for "Part3" is inside a success handler function that is held by the $q service and invoked after data has arrived from the server and the XHR completes.

“Part4”的控制台日志不必等待数据从服务器返回。它在XHR启动后立即执行。 “Part3”的控制台日志位于成功处理函数内部，该函数由$ q服务保存，并在数据从服务器到达并且XHR完成后调用。

For more information, see How to use $http promise response outside success handler.

有关更多信息，请参阅如何在成功处理程序外使用$ http promise响应。

Demo

console.log("Part 1");
console.log("Part 2");
var promise = new Promise(r=>r());
promise.then(function() {
    console.log("Part 3");
});
console.log("Part *4*");