javascript - 创建 AngularJS 指令时 '?ngModel' 的意义是什么？

Question

我正在学习新的 ng-book。关于过滤器的章节包括使用以下代码定义解析器的部分:

angular.module('myApp')
.directive('oneToTen', function() {
    return {
        require: '?ngModel';

我第一次看到 '?ngModel' 语法，Angular API 文档没有提供太多帮助。此语法表示什么？

谢谢!

Answer 1

? 是可选指令，^ 是父指令

http://docs.angularjs.org/api/ng.$compile

(no prefix) - Locate the required controller on the current element. Throw an error if not found.
? - Attempt to locate the required controller or pass null to the link fn if not found.
^ - Locate the required controller by searching the element's parents. Throw an error if not found.
?^ - Attempt to locate the required controller by searching the element's parents or pass null to the link fn if not found.