我的foreach循环中有什么错误？

Question

以下是我的多维数组命名$prev_map_data：

Array 
(
    [0] => Array 
     (
      [class_id] => 2 
      [class_name] => II 
      [class_checked] => 1 
      [class_subjects] => Array 
       (
        [0] => Array 
         (
          [cs_map_id] => 81 
          [subject_name] => 11 Engllish 
          [subject_checked] => 1 
          [teacher_cs_id] => 81 
         ) 

       ) 

     ) 
[1] => Array 
    (
     [class_id] => 3 
     [class_name] => III 
     [class_checked] => 1 
     [class_subjects] => Array 
      (
       [0] => Array 
        (
         [cs_map_id] => 155 
         [subject_name] => Hidi 
         [subject_checked] => 1 
         [teacher_cs_id] => 155 
        ) 

       [1] => Array 
        (
         [cs_map_id] => 156 
         [subject_name] => 11 Maths 
         [subject_checked] => 1 
         [teacher_cs_id] => 156 
        ) 

       [2] => Array 
        (
         [cs_map_id] => 157 
         [subject_name] => 11 Science 
         [subject_checked] => 1 
         [teacher_cs_id] => 157 
        ) 

      ) 

    ) 

）

我想通过一个从关键[class_id]一个得到所有的值和数组$data推值。但得到警告

Warning: Invalid argument supplied for foreach() 

我不明白我的代码有什么问题。任何人都可以帮助我改进我的代码并将值附加到新数组中吗？提前致谢。我的代码如下：

$prev_map_data = $objTeacherClassesSubjects->GetClassSubjectMappingsbyTeacherId ($request, $teacher_class_subjects_error_messages); 
    foreach($prev_map_data as $map_id) { 
       $cls_data[] = $map_id['class_id']; 
      } 
    } 

Answer 1

试试这个代码

$teacher_class_subjects_error_messages); 
    foreach($prev_map_data as $iKey => $iVal) { 
       $cls_data[] = $iVal['class_id']; 
      } 
    } 

Answer 2

$prev_map_data不是一个数组。使用var_export($prev_map_data);来查看它是否是数组

Answer 3

if(!empty($prev_map_data) && is_array($prev_map_data)) { 
    foreach($prev_map_data as $key=>$map_id) { 
    if(is_array($map_id)) 
     $cls_data[] = $map_id['class_id']; 
    else 
     echo '$map_id is not an array!'; 
    } 
} else { 
    echo '$prev_map_data is not an array or it is empty!'; 
}