javascript asp教程第十一课--Application 对象
2018-09-06 12:13
Overview:
The Application Object represents a collection of ASP pages. The Application object has zero (0) properties, two (2) collections, two (2) methods, and two (2) events.
Get Started:
Below are a couple scripts for lesson11.
<%@LANGUAGE=JavaScript%> <% //No ASP Here, just a regular HTML Page %> <HTML> <FORM ACTION=script11a.asp METHOD=Post> <STRONG>Would you like to chose the official Application color?</STRONG><BR> <SELECT NAME=OfficialColor> <OPTION>red</OPTION> <OPTION>white</OPTION> <OPTION>blue</OPTION> </SELECT><BR> <INPUT TYPE=Submit VALUE=Yes, click here> </FORM> No, <A HREF=script11a.asp>click here</A>. </HTML>
Click Hereto run script11.asp in a new window. Below is script11a.asp.
<%@LANGUAGE=JavaScript%> <HTML> <% Application.Lock() var OfficialColor = new String( Request.Form(OfficialColor) ) if (OfficialColor==red) { Application(OfficialColor) = red } if (OfficialColor==white) { Application(OfficialColor) = white } if (OfficialColor==blue) { Application(OfficialColor) = blue } if (OfficialColor==undefined) { //Do nothing. Just leave the color alone. } Application.Unlock() %> <BODY BGCOLOR=<%=Application(OfficialColor)%>> <STRONG> The official application color is <%=Application(OfficialColor)%>.<BR> </STRONG> </BODY> </HTML>
Application Collections:
The two collections are Contents and StaticObjects. StaticObjects come in the form of the <OBJECT> flag. Thats done in the global.asa that we saw in Lesson 09. Ill demonstrate it again down below.
By contrast, the Contents collection is demonstrated above. It allows you to set and retrieve variables with Application scope. The format for setting an Application variable is . However, since Contents is the default Collection, we have a little shortcut for setting Application variables. The shortcut goes like this: Application(VariableName)=VariableValue.
Share the Variable:
One last thought on Application Variables. The application variable is shared by all visitors. Lets say that you and I are on the same ASP web site at the same time. If you set the background color to white in script11.asp, then I will see white as the official color if I go directly to script11a.asp. Application Variables are by no means the most efficient means of passing information from one user to another.
No Apartment Model:
You may notice that the example above seems to be inefficient. Why not just directly assign Application(OfficialColor) = Request.Form(OfficialColor)? Because we cant. By design, the newer (and updated) versions of Microsoft server software intentionally do not support Apartment Model Behavior.
Application Methods:
The two Application Methods are Lock() and Unlock(). Lock() blocks all other users from changing the Application variables. Unlock() releases control so that other users can change it. Thats important on a larger site where multiple users may be trying to access the same page at the same time.
Application Events:
The two Application events are Application_OnStart() and Application_OnEnd(). These events are accessed in the global.asa. Lets repeat that script from lesson 09.
<OBJECT RUNAT=Server SCOPE=Session ID=MyInfo PROGID=MSWC.MyInfo> </OBJECT> <SCRIPT RUNAT=Server LANGUAGE=JavaScript> function Application_OnStart() { Application(someVariableName)=some value } function Application_OnEnd() { Application.Contents.RemoveAll() } function Session_OnStart() { Session.Timeout=15 } function Session_OnEnd() { //Do Nothing } </SCRIPT> <!-- METADATA TYPE=typelib FILE=C:\Program Files\Common Files\System\ado\msado15.dll -->
Misc. Items:
Application.Contents has two methods of its own. Application.Contents.Remove(VariableName) and Application.Contents.RemoveAll().
Youll notice there are also Session Events in the global.asa. Well deal with those in Lesson 12. Youll also notice a call to the ADO Library. Well talk about that when we get to databases.
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