title: Correctly creating an antd Form using the extends React.Component mechanism
body: <p>I am trying to reproduce the antd Form example in <a href="https://github.com/ant-design/ant-design/blob/master/components/form/demo/horizontal-login.md" rel="noreferrer">https://github.com/ant-design/ant-design/blob/master/components/form/demo/horizontal-login.md</a></p>
  
  <p>Replacing React.createClass with extends React.Component but I am getting a Uncaught TypeError: Cannot read property 'getFieldDecorator' of undefined</p>
  
  <p>with the following code:</p>
  
  <pre><code>import { Form, Icon, Input, Button } from 'antd';
  const FormItem = Form.Item;
  
  export default class HorizontalLoginForm extends React.Component {
      constructor(props) {
          super(props);
      }
  
    handleSubmit(e) {
      e.preventDefault();
      this.props.form.validateFields((err, values) =&gt; {
        if (!err) {
          console.log('Received values of form: ', values);
        }
      });
    },
    render() {
      const { getFieldDecorator } = this.props.form;
      return (
        &lt;Form inline onSubmit={this.handleSubmit}&gt;
          &lt;FormItem&gt;
            {getFieldDecorator('userName', {
              rules: [{ required: true, message: 'Please input your username!' }],
            })(
              &lt;Input addonBefore={&lt;Icon type="user" /&gt;} placeholder="Username" /&gt;
            )}
          &lt;/FormItem&gt;
          &lt;FormItem&gt;
            {getFieldDecorator('password', {
              rules: [{ required: true, message: 'Please input your Password!' }],
            })(
              &lt;Input addonBefore={&lt;Icon type="lock" /&gt;} type="password" placeholder="Password" /&gt;
            )}
          &lt;/FormItem&gt;
          &lt;FormItem&gt;
            &lt;Button type="primary" htmlType="submit"&gt;Log in&lt;/Button&gt;
          &lt;/FormItem&gt;
        &lt;/Form&gt;
          )
      }
  }
  </code></pre>
  
  <p>Looks like the missing Form.create part is causing the issue, but don't know where it fits using the extends mechanism.</p>
  
  <p>How can I properly do it ?</p>