Programming of ASP. NET Server controls

When a user requests a page, the server sends a piece of text to the client, including the printable characters and unprintable text. When the text arrives at the client, then, the visual markup characters are converted to visualized display to the user through the client browser such as IE. Therefore, when the user requests An aspx page, the Asp.net Server Control on the page, it will also write the text into the returned text stream. In this chapter, we will describe this process and learn ASP. NET Server Control programming knowledge.

ASP. NET Server Control programming provides four rendering Methods: Render, RenderChildren, RenderContents, and RenderControl. Each of these four methods has an HtmlTextWriter type parameter. HtmlTextWriter is used to write the markup characters and text into the inverted Asp.net Server Control Stream, Which is System. web. all the base classes of the UI namespace that Mark writers, including ChtmlTextWriter, Html32TextWriter, and XhtmlTextWriter, are used to write elements, attributes, styles, and layout information for different tag types.

Since there are four rendering methods, what are their functions? What are the differences between them? The following describes how to generate a control:

Each page has a control tree that represents all the child controls on the page. The page control is the root of the Control tree. to generate the control tree, an HtmlTextWriter class instance is created on the page; the corresponding stream is encapsulated in this instance, and the page passes the HtmlTextWriter object to RenderControl. RenderControl checks whether the Visible attribute of the control is true. If it is true, RenderControl calls the Render method, the Render method calls RenderContents. The RenderContents method is used to present the control content to the specified writer. If the control has child controls, the Render method passes HtmlTextWriter to the RenderChildren method, the RenderChildren method is used to generate child controls for controls.

An example is provided to illustrate the programming process of ASP. NET Server controls.

 
 

  
  
public class Class1 : WebControl  
  
  
{  
  
  
protected override void Render  
  
  
(System.Web.UI.HtmlTextWriter writer)  
  
  
{  
  
  
writer.Write("RenderChildren〈br 〉");  
  
  
base.Render(writer);  
  
  
}  
  
  
 
  
  
protected override void RenderChildren  
  
  
(System.Web.UI.HtmlTextWriter writer)  
  
  
{  
  
  
writer.Write("RenderChildren〈br 〉");  
  
  
base.RenderChildren(writer);  
  
  
}  
  
  
 
  
  
public override void RenderControl  
  
  
(System.Web.UI.HtmlTextWriter writer)  
  
  
{  
  
  
writer.Write("RenderControl〈br 〉");  
  
  
base.RenderControl(writer);  
  
  
}  
  
  
 
  
  
protected override void RenderContents  
  
  
(System.Web.UI.HtmlTextWriter writer)  
  
  
{  
  
  
writer.Write("RenderContents〈br 〉");  
  
  
base.RenderContents(writer);  
  
  
}  
  
  
} 
 
 

Figure 1RenderControl-> Render-> RenderContents-> RenderChildren ):

 

In ASP. in NET Server Control Programming, parameter values of various HtmlTextWrite methods use three enumeration types: HtmlTextWriteTag, HtmlTextWriteAttribute, and HtmlTextWriteStyle, which are not described in detail here. For example, Figure 2 shows the effect:

 
 

  
  
[DefaultProperty ("Text")]
  
  
[ToolboxData ("<{ 0}: WebCustomControl1
  
  
Runat = server> </{0}: WebCustomControl1> ")]
  
  
PublicClass WebCustomControl1: WebControl
  
  
{
  
  
Protected override void Render
  
  
(HtmlTextWriterOutput)
  
  
{
  
  
//----------------------------------------- 
  
  
// The first method, throughAdd+ [Attribute,
  
  
StyleAttribute, BeginTag \ EndTag]
  
  
// Addattriattribute, AddStyleAttribute
  
  
Before RenderBeginTag and RenderEndTag
  
  
Output. BeginRender (); // start Render
  
  
Output. Addattriter( HtmlTextWriterAttribute.
  
  
Value,"This is input .");
  
  
// Use HtmlTextWriteAttribute for enumeration
  
  
Output. AddStyleAttribute (HtmlTextWriterStyle.
  
  
BackgroundColor, ColorTranslator. ToHtml
  
  
(Color. GreenYellow ));
  
  
// Use HtmlTextWriteStyle Enumeration
  
  
Output. RenderBeginTag (HtmlTextWriterTag. Input );
  
  
// Use HtmlTextWriteTag for enumeration
  
  
Output. RenderEndTag ();
  
  
Output. EndRender (); // end Render
  
  
//------------------------------------------ 
  
  
 
  
  

  
  
//------------------------------------------- 
  
  
// Method 2: Write + [Attribute,
  
  
StyleAttribute, BeginTag \ EndTag]
  
  
// WriteAttribute and WriteStyleAttribute
  
  
Between WriteBeginTag and WriteEndTag
  
  
Output. WriteBeginTag ("Input");
  
  
// Directly marked name, without the HtmlTextWriteTag Enumeration
  
  
Output. WriteAttribute ("Value","This is input too .");
  
  
// Directly use the attribute name, without the HtmlTextWriteAttribute Enumeration
  
  
Output. Write ("Style = \"");
  
  
Output. WriteStyleAttribute ("Background-color",
  
  
ColorTranslator. ToHtml (Color. Lavender ));
  
  
// Use style tags directly without HtmlTextWriteStyle Enumeration
  
  
Output. Write ("\"");
  
  
Output. Write (HtmlTextWriter. TagRightChar); // Add the ">" flag
  
  
Output. WriteEndTag ("Input");
  
  
//----------------------------------------------- 
  
  
 
  
  
// The second method is applicable to friends who are familiar with html.
  
  
}
  
  
}
 
 

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