Prompt for undefined variables: gradeList. How can you solve this problem? I beg you for answers.

Question

Answer 1

//定义可以在前面定义gradeList空数组就可以了
//例如
$gradeList=[];

This will not prompt the error of undefined variables

Answer 2

You can define the gradeList variable in front

$gradeList=null It should be because there is no data in your table $grade has no data and no foreach loop is performed