【導(dǎo)讀】是微軟.NETframework整體的一部分,它包含一組大量的編程用的類，在下列的二個(gè)部分中,你如何學(xué)會(huì)很適合的放。在.NETframework,和學(xué)會(huì)能在你的頁面中使用語言。假想你必須支持大量的編程語言-比如VisualBasic、C#和。括存取文件系統(tǒng)、與數(shù)據(jù)庫(kù)協(xié)同工作和操作字符串的方法。此外，這些語言包含相似的編程構(gòu)造。即使用VisualBasic寫的條件語句的語法不與用C++寫的不一樣,程序的功能也是相同的。最后，大多數(shù)的編程語言有相似的數(shù)據(jù)變量類型。舉例來說，整型數(shù)據(jù)最大值和最小值可能依賴。對(duì)于多種語言來說維持這一功能需要很大的工作量。.NET類庫(kù)不完全是那樣。包含更多特殊的類用在正則表達(dá)式和處理Web協(xié)議。整型、字節(jié)型、字符型和數(shù)組。你需要了解當(dāng)你構(gòu)建.NET頁面的時(shí)候能夠訪問.NETframework的任意類。正如你猜測(cè)的,.NETframework是龐大的。.NETframework的類被組織成有層次結(jié)構(gòu)的命名空。在先前的ASP中，你僅僅能夠訪問五個(gè)標(biāo)準(zhǔn)類。相比之下提供超過。集合在命名空間中。機(jī)數(shù)字和日期的類。不支持VBScript，而且這是好消息。程序用戶處理控件也頁面事件。

　　

【正文】 with any version of Netscape Navigator. Requiring Fields: The RequiredFieldValidator Control You use RequiredFieldValidator in a Web form to check whether a control has a value. Typically, you use this control with a TextBox control. However, nothing is wrong with using RequiredFieldValidator with other input controls such as RadioButtonList. Validating Expressions: The RegularExpressionValidator Control You can use RegularExpressionValidator to match the value entered into a form field to a regular expression. You can use this control to check whether a user has entered, for example, a valid address, telephone number, or username or password. Samples of how to use a regular expression to perform all these validation tasks are provided in the following sections. 16 Comparing Values: The CompareValidator Control The CompareValidator control performs parisons between the data entered into a form field and another value. The other value can be a fixed value, such as a particular number, or a value entered into another control. Summarizing Errors: The ValidationSummary Control Imagine that you have a form with 50 form fields. If you use only the Validation controls discussed in the previous sections of this chapter to display errors, seeing an error message on the page might be difficult. For example, you might have to scroll down to the 48th form field to find the error message. Fortunately, Microsoft includes a ValidationSummary control with the Validation controls. You can use this control to summarize all the errors at the top of a page, or wherever else you want. 4. Advanced Control Programming Working with View State By default, almost all controls retain the values of their properties between form posts. For example, if you assign text to a Label control and submit the form, when the page is rendered again, the contents of the Label control are preserved. The magic of view state is that it does not depend on any special server or browser properties. In particular, it does not depend on cookies, session variables, or application variables. View state is implemented with a hidden form field called VIEWSTATE that is automatically created in every Web Forms Page. When used wisely, view state can have a dramatic and positive effect on the performance of your Web site. For example, if you display database data in a control that has view state enabled, you do not have to return to the database each time the page is posted back to the server. You can automatically preserve the data within the page39。s view state between form posts. Displaying and Hiding Content Imagine that you are creating a form with an optional section. For example, imagine that you are creating an online tax form, and you want to display or hide a section that contains questions that apply only to married tax filers. 17 Or, imagine that you want to add an additional help button to the tax form. You might want to hide or display detailed instructions for pleting form questions depending on a user39。s preferences. Finally, imagine that you want to break the tax form into multiple pages so that a person views only one part of the tax form at a time. In the following sections, you learn about the properties that you can use to hide and display controls in a form. You learn how to use the Visible and Enabled properties with individual controls and groups of controls to hide and display page content. Using the Visible and Enabled Properties Every control, including both HTML and Web controls, has a Visible property that determines whether the control is rendered. When a control39。s Visible property has the value False, the control is not displayed on the page。 the control is not processed for either prerendering or rendering. Web controls (but not every HTML control) have an additional property named Enabled. When Enabled has the value False and you are using Inter Explorer version or higher, the control appears ghosted and no longer functions. When used with other browsers, such as Netscape Navigator, the control might not appear ghosted, but it does not function. Disabling View State In certain circumstances, you might want to disable view state for an individual control or for an page as a whole. For example, you might have a control that contains a lot of data (imagine a RadioButtonList control with 1,000 options). You might not want to load the data into the hidden __VIEWSTATE form field if you are worried that the form data would significantly slow down the rendering of the page. Using Rich Controls In the following sections, you learn how to use three of the more featurerich controls in the framework. You learn how to use the Calendar control to display interactive calendars, the AdRotator control to display rotating banner advertisements, and the HTMLInputFile control to accept file uploads. McDonald, Zipuzita the Advanced Programming (2nd Edition)