从指令内部 $watch 对 ngModel 的外部更改的正确方法

Question

我正在尝试制定一个从两个输入源读取的指令，然后做一些事情将其变成一个。为此，我正在监听两个输入的变化，并将新的组合值分配给指令的 ngModel。

问题是我还需要知道何时在指令外修改 ngModel 以执行反向过程并正确设置我的两个指令输入源的值。有正确的方法吗？

我做了一个片段来更好地说明问题，这不是我的实际指令。

angular.module('myapp', [])

.controller('AppController', function($scope, $timeout) {
  $scope.data = {
    value: ''
  };
  
  $timeout(function() {
    $scope.data.value = 'hellooooo';
  }, 5000);
})

.directive('sampleDirective', function() {
  return {
    require: 'ngModel',
    restrict: 'E',
    template: '<input ng-model="data.input1" ng-change="changed()"><input ng-model="data.input2" ng-change="changed()">',
    scope: {
      ngModel: '='
    },
    controller: function($scope) {
      $scope.data = {};
      $scope.changed = function() {
        $scope.ngModel = $scope.data.input1 + ' + ' + $scope.data.input2;  
      }
      
      // The watch is running even when the ngModel is modified inside the changed function above 
      // I want it to only run when the model is changed from outside the directive, like
      // I'm doing in the AppController.
      $scope.$watch('ngModel', function(value) {
        if (value) {
          // Just simulating some processing
          var length = value.length;
          
          $scope.data.input1 = value.slice(0, length/2);
          $scope.data.input2 = value.slice(length/2, length-1);
        }
      });
    }
  };
});

<div ng-app="myapp">
  
  <div ng-controller="AppController">
    <sample-directive ng-model="data.value"></sample-directive>

    <br>
    <br>
    <div>{{ data.value }}</div>
  </div>
</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.4.3/angular.js"></script>

Answer 1

相当奇怪的要求，但您可以更改指令以使用 ngModelController 代替

.directive('sampleDirective', function() {
  return {
    require: 'ngModel',
    restrict: 'E',
    template: '<input ng-model="data.input1" ng-change="changed()"><input ng-model="data.input2" ng-change="changed()">',
    scope: {
      ngModel: '='
    },
    link: function(scope, element, attributes, ngModelCtrl) {
      // This will be called when it is changed from outside the directive
      ngModelCtrl.$formatters.push(function(value) {
        if (value) {
          // Just simulating some processing
          var length = value.length;

          scope.data.input1 = value.slice(0, length/2);
          scope.data.input2 = value.slice(length/2, length-1);
        }
        return value;
      });

      scope.changed = function() {
        // Set the model value from inside the directive
        ngModelCtrl.$setViewValue(scope.data.input1 + ' + ' + scope.data.input2);
      }
    },
    controller: function($scope) {
      $scope.data = {};
    }
  };
})

Answer 2

您拥有的是自定义输入控件。它是一个具有 2 个文本框的输入控件，但 "model" 实际上是两者的组合。

要实现 "supports" ngModel 的自定义输入控件，即与 require: ngModel 的其他指令集成，您的指令还需要 require: ngModel 并使用 ngModelController 要集成的挂钩。

所以，不要只做 scope: { ngModel: "=" }。这样，您就可以双向绑定到附加到 ng-model 属性的模型，但是当您使用 scope.ngModel = "something".

设置此值时，事情不会像您期望的那样工作

Angular 提供了一个 example of a custom input control in its documentation of ngModelController。简而言之，您需要协调设置 $viewValue - 当基础视图发生变化时，并设置视图 - 当模型发生变化时。

.directive("sampleDirective", function(){
  return {
    require: "ngModel",
    scope: true,
    template: '<input ng-model="d.input1" ng-change="viewChanged()">\
               <input ng-model="d.input2" ng-change="viewChanged()">',

    link: function(scope, element, attrs, ngModel){
      var d = scope.d = {};      

      ngModel.$render = render;

      scope.viewChanged = read;


      // defines how to render based on model changes
      function render(){
        var modelValue = ngModel.$modelValue || "";
        var length = modelValue.length;

        d.input1 = modelValue.slice(0, length/2);
        d.input2 = length > 1 ? modelValue.slice(length/2, length) : "";
      };


      // defines how to set the model based on DOM changes
      function read(){
        var newViewValue = d.input1 + d.input2;
        ngModel.$setViewValue(newViewValue);
      }
    }
  };
});

然后，您的控件将与任何其他支持 ngModel 的指令一起工作，例如 required 或 ng-pattern 或 ng-change，并且可以参与表单验证：

<div ng-form="form1">
  <sample-directive ng-model="foo" maxlength="8" ng-change="doSomething()">
  </sample-directive>
</div>

Demo

从指令内部 $watch 对 ngModel 的外部更改的正确方法

Proper way to $watch external changes to a ngModel from inside a directive

javascript

angularjs

angularjs-directive

angularjs-scope

isolate-scope