為什么那個(gè).error和.red方法都沒(méi)有被調(diào)用到，檢查了好幾遍還是沒(méi)找到問(wèn)題所在?。。。?！

樣式

<style>

.red{

background: #a30;

}

.error{

border: 1px solid #a10;

}

</style>

表單：

<form name="signUpForm" action="" ng-submit="submitForm()">

<div class="form-group">

<label>用戶(hù)名：</label>

<input class="form-control"?

ng-model="username"

name="username"

ng-class="{ 'error': signUpForm.username.$invalid && $touched}"

class="form-control"

ng-minlength = "4"

maxlength="10"?

required

>

</div>

</form>