validateTrigger 'onBlur' can't use In react-native TextInput

I use the example of the react-native. After add validateTrigger, the value always to be empty, when the TextInput blur.

"react": "^16.2.0", "react-native": "0.53.3", "rc-form": "^2.1.7",

{getFieldDecorator('username', {
          validateFirst: true,
          validateTrigger: 'onBlur', // **add code here**
          rules: [
            { required: true, message: '请输入手机号!' },
            {
              pattern: /^1\d{10}$/,
              message: '请输入正确的手机号!',
            },
            {
              validator: (rule, value, callback) => {
                this.checkUserNameOne(value, callback);
              },
              message: '手机号已经被注册!',
            },
          ],
        })(
          <FromItem
            autoFocus
            placeholder="手机号"
            error={getFieldError('username')}
          />
        )}

Can you help me to explain it?