Fatal error: Class 'Redis' not found in Windows

Question

This is my php.ini:

extension=php_igbinary.dll

extension=php_redis.dll

This is my phpinfo:

igbinary

redis

Whe I was run the code like this:

$redis = new \Redis();

echo $redis;exit();

The question is:

Fatal error: Class 'Redis' not found in D:\www\test.php on line 2
PHP Fatal error:  Class 'Redis' not found in D:\www\test.php on line 2

Who can tell me why And what should I do！