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Component Actions
In component actions, the component currently being displayed defines the action method to be performed. For example, the first page of a WebObjects application is the Main component, so Main defines the first action method to be performed.To associate the component's action method to a user action, you map it to a dynamic element that has an attribute named action (such as a WOSubmitButton, WOActiveImage, or WOHyperlink). When the user performs the associated action, your method is invoked. For example, in the HelloWorld example application, the submit button is mapped to a method named sayHello in the Main component. When a user types in a name and clicks the button on the main page, it initiates the application's request-response loop, and sayHello is invoked.
Action methods take no arguments and return a page (component) that will be packaged with an HTTP response. For example, the sayHello method creates a new page named Hello and sends that page the name the user has typed into the text field.
//WebScript HelloWorld Main.wosIf you're programming in Java, the sayHello method looks like this:
- sayHello
{
id nextPage;
nextPage = [self pageWithName:@"Hello"];
[nextPage setVisitorName:visitorName];
return nextPage;
}
//Java HelloWorld Main.javaIn this example, the component Main is used to generate the page that handles the user request, and the component Hello generates the page that represents the response. Main is the request component or the request page, and Hello is the response component or the response page.
public WOComponent sayHello() {
Hello nextPage = this.pageWithName("Hello");
nextPage.setVisitorName(visitorName);
return nextPage;
}
It's common for action methods to determine the response page based on user input. For example, the following action method returns an error page if the user has entered an invalid part number (stored in the variable partnumber); otherwise, it returns an inventory summary:
// WebScript exampleComponent action methods don't have to return a new page. They can instead direct the application to use the request page as the response page by returning nil (null in Java). For example, the following action method records the name of the last visitor, clears the text field, and redraws the Main component, which contains it:
- showPart {
id errorPage;
id inventoryPage;
if ([self isValidPartNumber:partnumber]) {
errorPage = [self pageWithName:@"Error"];
[errorPage setErrorMessage:@"Invalid part number %@.",
partnumber];
return errorPage;
}
inventoryPage = [self pageWithName:@"Inventory"];
[inventoryPage setPartNumber:partnumber];
return inventoryPage;
} // Java example
public WOComponent showPart() {
Error errorPage;
Inventory inventoryPage;
if (isValidPartNumber(partNumber)) {
errorPage = (Error)this.pageWithName("Error");
errorPage.setErrorMessage("Invalid part number " +
partnumber);
return errorPage;
}
inventoryPage = (Inventory)this.pageWithName("Inventory");
inventoryPage.setPartNumber(partnumber);
return inventoryPage;
}
// WebScript Main.wosNote: Always return nil (null) in an action method instead of returning self (this). Returning nil uses the request component as the response component. Returning self uses the current component as the response component. At first glance, these two return values seem to do the same thing. However, if the action method is in a component that's nested inside of the request component, a return value of self will make the application try to use the nested component, which represents only a portion of the page, as the response component. This, most likely, is not what you want. Therefore, it is safer to always return nil.
- recordMe
{
if ([aName length]) {
[[self application] setLastVisitor:aName];
[self setAName:@""]; // clear the text field
}
} // Java Main.java
public WOComponent recordMe
{
if (aName.length != 0) {
((Application)application()).setLastVisitor(aName);
aName = ""; // clear the text field
}
return null;
}
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