tp5版本环境下。
源数据数组：
array(12) {
[0] => array(7) {
["category_id"] => int(1)
["category_name"] => string(32) "水产肉类/新鲜蔬果/熟食"
["category_parentid"] => int(0)
["category_level"] => int(0)
["category_model"] => string(1) "0"
["category_order"] => int(0)
["level"] => int(0)
}
[1] => array(7) {
["category_id"] => int(2)
["category_name"] => string(13) "蛋/蛋制品"
["category_parentid"] => int(1)
["category_level"] => int(1)
["category_model"] => string(1) "0"
["category_order"] => int(0)
["level"] => int(1)
}
[2] => array(7) {
["category_id"] => int(3)
["category_name"] => string(22) "加工蛋类/蛋制品"
["category_parentid"] => int(2)
["category_level"] => int(2)
["category_model"] => string(1) "0"
["category_order"] => int(0)
["level"] => int(2)
}
[3] => array(7) {
["category_id"] => int(5)
["category_name"] => string(13) "松花/皮蛋"
["category_parentid"] => int(3)
["category_level"] => int(3)
["category_model"] => string(1) "0"
["category_order"] => int(0)
["level"] => int(3)
}
[4] => array(7) {
["category_id"] => int(6)
["category_name"] => string(9) "咸鸭蛋"
["category_parentid"] => int(3)
["category_level"] => int(3)
["category_model"] => string(1) "0"
["category_order"] => int(0)
["level"] => int(3)
}
[5] => array(7) {
["category_id"] => int(7)
["category_name"] => string(6) "喜蛋"
["category_parentid"] => int(3)
["category_level"] => int(3)
["category_model"] => string(1) "0"
["category_order"] => int(0)
["level"] => int(3)
}
[6] => array(7) {
["category_id"] => int(4)
["category_name"] => string(12) "鲜活蛋类"
["category_parentid"] => int(2)
["category_level"] => int(2)
["category_model"] => string(1) "0"
["category_order"] => int(0)
["level"] => int(2)
}
[7] => array(7) {
["category_id"] => int(8)
["category_name"] => string(6) "鸡蛋"
["category_parentid"] => int(4)
["category_level"] => int(3)
["category_model"] => string(1) "0"
["category_order"] => int(0)
["level"] => int(3)
}
[8] => array(7) {
["category_id"] => int(9)
["category_name"] => string(6) "鸭蛋"
["category_parentid"] => int(4)
["category_level"] => int(3)
["category_model"] => string(1) "0"
["category_order"] => int(0)
["level"] => int(3)
}
[9] => array(7) {
["category_id"] => int(10)
["category_name"] => string(6) "鹅蛋"
["category_parentid"] => int(4)
["category_level"] => int(3)
["category_model"] => string(1) "0"
["category_order"] => int(0)
["level"] => int(3)
}
[10] => array(7) {
["category_id"] => int(11)
["category_name"] => string(6) "零食"
["category_parentid"] => int(0)
["category_level"] => int(0)
["category_model"] => string(1) "0"
["category_order"] => int(0)
["level"] => int(0)
}
[11] => array(7) {
["category_id"] => int(12)
["category_name"] => string(6) "干果"
["category_parentid"] => int(11)
["category_level"] => int(1)
["category_model"] => string(1) "0"
["category_order"] => int(0)
["level"] => int(1)
}
}

模板调用
{foreach name="lis" item="vo" key="k" }
<li>
{$vo.category_name}
{foreach name="vo.son" item="vo1" key="k1" }
<ul>
<li>
{$vo1.category_name}
{foreach name="vo.son.son" item="vo2" key="k2" }
{$vo2.category_name}
{/foreach}
</li>
</ul>
{/foreach}
</li>
{/foreach}

循环第3个子类的时候提示错误“未定义数组索引: son”；
按理说模板循环是一个二维数组，我的son子类也是一个子二维数组怎么就出错了呢