From version 2.0.4 there is the new EachValidator which makes it more easy now:

['x', 'each', 'rule' => ['integer']],

This should be sufficient. If the values should be also checked you could use this (with the 'in' validator which actually is the RangeValidator):

['x', 'each', 'rule' => ['in', 'range' => [2, 4, 6, 8]]], // each value in x can only be 2, 4, 6 or 8

However, you can use this 'in' validator also directly. And that is possible with Yii versions before 2.0.4:

['x', 'in', 'range' => [2, 4, 6, 8], 'allowArray' => true]

The use of 'strict' => true would probably makes no sense in case the data is sent by the client and is set with Model->load(). I'm not quite sure but I think those values are all sent as strings (like "5" instead of 5).

ADDON:

You may need to create custom validation rules like below:

['x','checkIsArray']

Then in your model, impelement checkIsArray:

public function checkIsArray(){

if(!is_array($this->x)){

$this->addError('x','X is not array!');

}

}

You can do all you need into a custom validation rule.

As emte mentioned on comment, you can also use inline validator with anonymous function like below:

['x',function ($attribute, $params) {

if(!is_array($this->x)){

$this->addError('x','X is not array!');

}

}]