透过以这些建构来间接存取内部栏位，您可以防范无效的输入值。

By using these constructs for indirect access to internal fields, you can guard against invalid input values.

youdao

如果用户输入无效的数据片段，应用程序可立即提示用户，在用户提交页面之前改正问题。

If the user enters an invalid piece of data, the application can immediately prompt the user to correct it before he submits the page.

youdao

只第二种方法是不够的，因为只用这种方法仍然可能输入无效的值。

The second method is insufficient because it is still possible to enter an invalid value.

youdao