RequiredFieldValidator控件默认检查非空字符串（空格不算在内）。在RequiredFieldValidator关联的表单字段中输入任何字符，该RequiredFieldValidator控件就不会显示它的验证错误信息。

RequiredFieldValidator控件用于要求用户在提交表单前为表单字段输入值。使用Required- FieldValidator控件时，必须设置两个重要的属性：-The RequiredFieldValidator control default check non-empty string (spaces do not count). Enter any character in the a RequiredFieldValidator associated form field RequiredFieldValidator control does not display validation error information. RequiredFieldValidator control to require the user to enter a value for the form fields before the form is submitted. When using the the Required-FieldValidator control, you must set two important properties: