angularjs - 为什么在角度指令`ngForm`中使用“preLink”函数，而不是常规的“postLink”函数？

Question

在 angular.js 中，在 ngForm(form) 指令定义中，compile 函数只返回一个preLink函数。为什么它应该preLink代替 common postLink？

以下代码来自 angular.js master 分支：

var formDirective = {
  name: 'form',
  restrict: isNgForm ? 'EAC' : 'E',
  controller: FormController,
  compile: function ngFormCompile(formElement) {
    // Setup initial state of the control
    formElement.addClass(PRISTINE_CLASS).addClass(VALID_CLASS);
    return {
      pre: function ngFormPreLink(scope, formElement, attr, controller) {
        // if `action` attr is not present on the form, prevent the default action (submission)
        if (!('action' in attr)) {
          // we can't use jq events because if a form is destroyed during submission the default
          // action is not prevented. see #1238
          //
          // IE 9 is not affected because it doesn't fire a submit event and try to do a full
          // page reload if the form was destroyed by submission of the form via a click handler
          // on a button in the form. Looks like an IE9 specific bug.
          var handleFormSubmission = function(event) {
            scope.$apply(function() {
            controller.$commitViewValue();
            controller.$setSubmitted();
          });
        event.preventDefault();
        };
        ...

Answer 1

pre-link 函数在任何子指令之前执行，因此它是准备任何数据以供子指令使用的好地方。我假设在这种情况下，它会准备提交处理程序，以防子指令在其 post-link 函数中提交表单。

实际上，链接函数的执行顺序是：

1. 父预链接
2. 子预链接
3. 子后链接
4. 父后链接