动态批改表单字段的配置

动态修改表单字段的配置
方法一：

myField.allowBlank = true;myField.validateValue(myField.getValue()); //force update

参考：
http://stackoverflow.com/questions/6098596/how-to-adding-fields-config-on-the-fly
http://www.sencha.com/learn/form-faq#Set_allowBlank_dynamically