如何在 Angular 1.5 组件中等待绑定（没有 $scope.$watch）

Question

我正在编写一个 Angular 1.5 指令，我运行遇到了一个令人讨厌的问题，试图在绑定数据存在之前对其进行操作。

这是我的代码：

app.component('formSelector', {
  bindings: {
    forms: '='
  },
  controller: function(FormSvc) {

    var ctrl = this
    this.favorites = []

    FormSvc.GetFavorites()
    .then(function(results) {
    ctrl.favorites = results
    for (var i = 0; i < ctrl.favorites.length; i++) {
      for (var j = 0; j < ctrl.forms.length; j++) {
          if (ctrl.favorites[i].id == ctrl.newForms[j].id) ctrl.forms[j].favorite = true
      }
     }
    })
}
...

如您所见，我正在调用 AJAX 来获取收藏夹，然后根据我绑定的表单列表进行检查。

问题是，甚至在填充绑定之前就已经实现了诺言...所以当我运行循环时，ctrl.forms 仍然是未定义的！

不使用 $scope.$watch（这是 1.5 组件的一部分）我如何等待绑定完成？

Answer 1

您可以使用新的生命周期挂钩，特别是$onChanges, to detect the first change of a binding by calling the isFirstChange method. Read more about this here。

这是一个例子：

<div ng-app="app" ng-controller="MyCtrl as $ctrl">
  <my-component binding="$ctrl.binding"></my-component>
</div>

<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.6.4/angular.js"></script>
<script>
  angular
    .module('app', [])
    .controller('MyCtrl', function($timeout) {
      $timeout(() => {
        this.binding = 'first value';
      }, 750);

      $timeout(() => {
        this.binding = 'second value';
      }, 1500);
    })
    .component('myComponent', {
      bindings: {
        binding: '<'
      },
      controller: function() {
        // Use es6 destructuring to extract exactly what we need
        this.$onChanges = function({binding}) {
          if (angular.isDefined(binding)) {
            console.log({
              currentValue: binding.currentValue, 
              isFirstChange: binding.isFirstChange()
            });
          }
        }
      }
    });
</script>

Answer 2

我有一个类似的问题，我这样做是为了避免在我要发送的值准备好之前调用组件：

<form-selector ng-if="asyncValue" forms="asyncValue" ></form-selector>

Answer 3

我遇到了类似的问题，我发现这篇文章很有帮助。 http://blog.thoughtram.io/angularjs/2016/03/29/exploring-angular-1.5-lifecycle-hooks.html

我有一个 ajax 调用在页面加载时命中服务器，我的组件需要 ajax return 值才能正确加载。我是这样实现的：

this.$onChanges = function (newObj) {
      if (newObj.returnValFromAJAX)
        this.returnValFromAJAX = newObj.returnValFromAJAX;
    };

现在我的组件可以完美运行了。作为参考，我使用 Angular 1.5.6

Answer 4

楼主说：

the promise is being fulfilled even before the binding is populated... sot hat by the time I run the loop, ctrl.forms is still undefined

自从 AngularJS 1.5.3 以来，我们有了 lifecycle hooks 并且为了满足 OP 的问题，您只需要移动取决于 [=11= 中满足的绑定的代码]:

$onInit() - Called on each controller after all the controllers on an element have been constructed and had their bindings initialized (and before the pre & post linking functions for the directives on this element). This is a good place to put initialization code for your controller.

因此在示例中：

app.component('formSelector', {
  bindings: {
    forms: '='
  },
  controller: function(FormSvc) {
    var ctrl = this;
    this.favorites = [];

    this.$onInit = function() {
      // At this point, bindings have been resolved.
      FormSvc
          .GetFavorites()
          .then(function(results) {
            ctrl.favorites = results;
            for (var i = 0; i < ctrl.favorites.length; i++) {
              for (var j = 0; j < ctrl.forms.length; j++) {
                if (ctrl.favorites[i].id == ctrl.newForms[j].id) {
                  ctrl.forms[j].favorite = true;
                }
              }
            }
          });
    }
}

所以是的，有一个 $onChanges(changesObj)，但是 $onInit() 专门解决了最初的问题，即我们什么时候可以保证绑定已经解决。

如何在 Angular 1.5 组件中等待绑定（没有 $scope.$watch）

How to wait for binding in Angular 1.5 component (without $scope.$watch)

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