yii2中验证码的使用--图片不显示

1.控制器中

public function actions()
    {
        return [
            'captcha' => [
                'class' => 'yii\captcha\CaptchaAction',
                'fixedVerifyCode' => YII_ENV_TEST ? 'testme' : null,
            ],
        ];
    }
2.模型中
要有一个验证码的字段$verifyCode
3.视图中
use yii\helpers\Html;

use yii\widgets\ActiveForm;

use yii\captcha\Captcha;
自动生成表单



 
页面中验证码代码
<?= $form->field($model, 'verifyCode')->widget(Captcha::className(), [

                    'template' => '<div class="row"><div class="col-lg-3">{image}</div><div class="col-lg-6">{input}</div></div>',

]) ?>
控制器中的权限可能导致验证码图片不显示，
public function behaviors()

    {

        return [

            'access' => [

                'class' => AccessControl::className(),

                'only' => ['logout', 'signup','login'],

                'rules' => [

                    [

                        'actions' => ['signup'],

                        'allow' => true,

                        'roles' => ['?'],

                    ],

                    [

                        'actions' => ['logout'],

                        'allow' => true,

                        'roles' => ['@'],

                    ],

                ],

            ],

            'verbs' => [

                'class' => VerbFilter::className(),

                'actions' => [

                    'logout' => ['post'],

                ],

            ],

        ];

    }
控制器中红线部分缺少则导致验证码不显示