angular ng-repeat expressions as variables

问题:

I'm trying to do something like this:

<ul>
    <li ng-repeat="{{myRepeatExpression}}">{{row.name}}</li>
</ul>

But because the ng-repeat logic is in the compile state of the directive it treats the {{myRepeatExpression}} as a normal string instead of a variable. Which doesn't work, obviously.

Is there any workaround for that?

回答1:

You can only use and expression with ng-repeat and not an interpolated value. Now in order to create a dynamic repeatable list you can try either:

1. using a function that returns the list dynamically in the ng-repeat - this is potentially more expensive since angular needs to call the function first then determine if the collection has changed when doing a $digest cycle
2. $watch for a particular variable on the scope that trigger a change of the list - potentially more efficient but if your dynamic list depends on more than one variable it can get more verbose and can lead to potential bugs from forgetting to add a new $watch when a new variable is required

Demo plunker

JS:

app.controller('MainCtrl', function($scope) {
  var values1 = [{name:'First'}, {name:'Second'}];
  var values2 = [{name:'Third'}, {name:'Fourth'}, {name:'Fifth'}];

  //1. function way
  $scope.getValues = function(id) {
    if(id === 1) {
      return values1;
    }
    if(id === 2) {
      return values2;
    }
  }

  //2. watch way
  $scope.values = undefined;
  $scope.$watch('id', function(newVal) {
    $scope.values = $scope.getValues(newVal);
  });
});

HTML:

<!-- Here we pass the required value directly to the function -->
<!-- this is not mandatory as you can use other scope variables and/or private variables -->
<ul>
  <li ng-repeat="v in getValues(id)">{{v.name}}</li>
</ul>
<!-- Nothing special here, plain old ng-repeat -->
<ul>
  <li ng-repeat="v in values">{{v.name}}</li>
</ul>

回答2:

ng-repeat only accepts it proprietary expression syntax as in row in rows, but rows could be a function or promise in your controller. However you need to watch performance closely as ng-repeat doesn't work well with things that change too often (the dreaded max. 10 iterations error).

回答3:

You can't use ng-repeat with string/variable that should represent the expression directly, but you can create directive that interpolate/parse this value and pass it to the ng-repeat argument and recompile the element.

app.directive('ngVarRepeat',function($compile){
  return {
    priority:1001, //must be higher than 1000 (priority of ng-repeat)
    compile:function($elm,$attrs){

      var expression = $attrs.ngVarRepeat;
      $elm.removeAttr('ng-var-repeat'); // remove attribute so we can recompile it later

      return function(scope,elm,attrs){
        $elm.attr('ng-repeat',scope.$eval(expression));
        $compile($elm)(scope);
      }
    }
  }
})

Take a look at this plunker: demo plunker from accepted answer

Also please note, that this approach should cause troubles in nested ng-repeats.