PHP: Undefined property stdClass, but the property is already exists

Below is my class.

class MaterialType {

    public $id;
    public $name;

    function getAllMaterialType() {
        $query = "SELECT * FROM material_types";
        $result = mysql_query($query);

   开发者_Go百科     $arr = array();
        while ($row = mysql_fetch_array($result)) {
            $arr[] = new MaterialType();
            $arr[]->id = $row['m_type_id'];
            $arr[]->name = $row['m_type_name'];
        }

        return $arr;
    }
}

The problem is when I create object in an array like above, and display it using foreach, there are errors that say Undefined property stdClass. I already defined the property that being used, so why these errors appear? Below is the code that I use to display data.

$materialTypeObj = new MaterialType();

foreach($materialTypeObj->getAllMaterialType() as $mat) {
    echo $mat->name;
}

Every time you do $array[] = it inserts a new element in the end of an array. What you need to do is:

class MaterialType {

public $id;
public $name;


function getAllMaterialType() {

    $query = "SELECT * FROM material_types";
    $result = mysql_query($query);

    $arr = array();
    while($row = mysql_fetch_array($result)) {
        $mat = new MaterialType();
        $mat->id = $row['m_type_id'];
        $mat->name = $row['m_type_name'];
        $arr[] = $mat;
    }

    return $arr;
}

}