Yii2未定义的索引

$array = ['foo' => 'bar'];
echo $array['baz']; // 未定义的索引异常

class MyClass {
    public $foo = 'bar';
}

$object = new MyClass();
echo $object->baz; // 未定义的属性异常

$array = ['foo' => 'bar'];
if (isset($array['baz'])) {
    echo $array['baz'];
} else {
    echo '索引不存在';
}

class MyClass {
    public $foo = 'bar';
}

$object = new MyClass();
if (property_exists($object, 'baz')) {
    echo $object->baz;
} else {
    echo '属性不存在';
}

use yii\helpers\ArrayHelper;

$array = ['foo' => 'bar'];
$value = ArrayHelper::getValue($array, 'baz', '默认值');
echo $value; // 输出默认值