AngularJS:何时在'scroll'事件中使用$ apply [英] AngularJS: when to use $apply in a 'scroll' event

问题描述

我有一条通过以下方式添加固定"类的指令:

I have a directive that adds 'fixed' class by:

ng-class='{ "fixed": fixed }'

指令具有以下功能:

angular.element($window)
  .on('scroll', function() {
    if (this.pageYOffset >= 480) {
      if (!scope.fixed) {
        scope.fixed = true;
        scope.$apply();
      }
    } else {
      if (scope.fixed) {
        scope.fixed = false;
        scope.$apply();
      }
    }
  });

我的问题是，是否应该像这样应用 scope.$ apply()，所以它仅在变量更改时才触发，或者只写就行:

My question is, should I apply the scope.$apply() like this, so it only fires whenever my variable changes, or is it ok just to write:

angular.element($window)
  .on('scroll', function() {
    if (this.pageYOffset >= 480) {
      scope.fixed = true;
    } else {
      scope.fixed = false;
    }
    scope.$apply();
  });

也许我不知道使用 scope.$ watch 的某些用途?

Maybe there's some use of scope.$watch that I am unaware of?

推荐答案

如果未进行更新，则调用 scope.$ apply()没有意义.因此，我建议您使用第一种方法:

It doesn't make sense to call scope.$apply() if no update is made. So I would suggest use your first approach which is :

   angular.element($window)
  .on('scroll', function() {
    if (this.pageYOffset >= 480) {
      if (!scope.fixed) {
        scope.fixed = true;
        scope.$apply();
      }
    } else {
      if (scope.fixed) {
        scope.fixed = false;
        scope.$apply();
      }
    }
  });

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