Question

我有一个定义如下的递归函数

private function _buildPathwayRecurse(&$category, &$reversePathway = array()) {
  $category->uri = FlexicontentHelperRoute::getCategoryRoute($category->id);
  $reversePathway[] = $category;

  if ($category->parent_id != 0) {
    $category = $this->_getCatForPathway($category->parent_id);
    $this->_buildPathwayRecurse($category, $reversePathway);
  } else {
    return $reversePathway;
  }
}

我正在这样称呼它

$reversePathway = $this->_buildPathwayRecurse($category);

然而$ reversePathway最终为null。知道为什么会这样吗？我已经使用XDebug逐步完成了我的代码，据我所知，一切正常。当我到达行

return $reversePathway

$ reversePathway看起来很完美。它持续通过函数调用并每次获得一个新项目。在执行返回线之前，它有一个像应该的一样的几个项目的数组，但到我出去的时候

$reversePathway = $this->_buildPathwayRecurse($category);

它似乎只是消失了！

Answer 1

您缺少一份退货声明。尝试

private function _buildPathwayRecurse(&$category, &$reversePathway = array()) {
$category->uri = FlexicontentHelperRoute::getCategoryRoute($category->id);
$reversePathway[] = $category;

if ($category->parent_id != 0) {
$category = $this->_getCatForPathway($category->parent_id);
return $this->_buildPathwayRecurse($category, $reversePathway); //no assignment,     the     function will be executed but even if the inner part goes to the else block, there's nothing to hold the returned value.
//nothing to return when it gets here.
  } else {
    return $reversePathway;
  }
}

Answer 2

if（）块告诉它递归或返回一个值。

第一次迭代显然会递归，因此它不会返回，所以构建数组的所有辛苦工作都不会从初始迭代中返回。

您可能希望它以任一方式返回，而不是使用else子句。

Answer 3

您的if块缺少返回语句。

private function _buildPathwayRecurse(&$category, &$reversePathway = array()) {
  $category->uri = FlexicontentHelperRoute::getCategoryRoute($category->id);
  $reversePathway[] = $category;

  if ($category->parent_id != 0) {
    $category = $this->_getCatForPathway($category->parent_id);
    $this->_buildPathwayRecurse($category, $reversePathway); //no assignment, the function will be executed but even if the inner part goes to the else block, there's nothing to hold the returned value.
    //nothing to return when it gets here.
  } else {
    return $reversePathway;
  }
}

递归函数不返回PHP中的值

3 个答案: