C# 4 and .NET 4

1194 ❘ ChaPTer 41 Asp.net feAtures
Note that this property isn’t as simple as just storing a value in a member field. This is due to the way
ASP.NET maintains state, as discussed in the previous chapter. Controls are instantiated on each postback
operation, so to store values you must make use of view state. This is easy to access — you simply use the
ViewState collection, which can store any object that is serializable. Otherwise, offset would revert to its
initial value between each postback.
To modify offset, you use a method called Cycle():
public void Cycle()
{
offset = ++offset;
}
This simply increments the value stored in the view state for offset.
Finally, you come to perhaps the most important method override for any custom control — Render(). This
is where you output HTML, and as such it can be a very complicated method to implement. If you were
to take into account all the browsers that may view your controls, and all the variables that could affect
rendering, this method could get very big. Fortunately, for this example, it’s quite simple:
}
}
protected override void Render(HtmlTextWriter output)
{
string text = Text;
for (int pos = 0; pos < text.Length; pos++)
{
int rgb = colors[(pos + offset) % colors.Length].ToArgb()
& 0xFFFFFF;
output.Write(string.Format(
"{1}", rgb, text[pos]));
}
}
This method gives you access to the output stream to display your control content. There are only two cases
where you don’t need to implement this method:
➤
➤
When you are designing a control that has no visual representation (usually known as a component)
When you are deriving from an existing control and don’t need to change its display characteristics
Custom controls can also expose custom methods, raise custom events, and respond to child controls (if
any). In the case of RainbowLabel, you don’t have to worry about any of this.
Next, you need to add a web page, Default.aspx, and add code to view the control and provide access to
Cycle(), as follows:
...
The required code in Default.aspx.cs is simply this:
code snippet PCSCustomCWebSite1/Default.aspx
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