Shulou(Shulou.com)06/02 Report--

This article will explain in detail how to use the Tapestry5 component event. The editor thinks it is very practical, so I share it with you as a reference. I hope you can get something after reading this article.

Component event

Component events refer to the user's behavior that the component perceives, such as clicking on a link or submitting a form.

Components are mainly used for two purposes:

◆ they present a request that a user triggers a link or form in a client browser. These are more fully described in page navigation (page navigation) and request processing (requst processing).

◆ they depict the flow of control in a request that allows a component to notify its container of situations (a form is submitted) or to collect fragments of data from the container.

Typically, a navigation request (initiated by the user) will generate many control flow requests. For example, the form component triggers an action request and then sends a notification event claiming that the form submission event will be handled, regardless of success.

In Tapestry 4, you can configure a parameter of a component with a method name that will be called when a particular event occurs (usually a request from the client). Such as:

< form jwcid= "@ Form" listener= "listener:someMethodName" >

This has some limitations, including the fact that only one method is called.

Tapestry 5 component events introduce event handling methods (event handler methods) identified by naming conventions or OnEvent annotation. Event handling methods can have any visibility, even private (usually they are package visibility to support testing).

Configure a specific method to be called compared to the Tapestry 5 component event, and you can identify one or more methods to listen for the component event. A single event handling method can receive notification events from many different components, such as adding @ OnEvent (component= {"component1", "component2"}) to the event handling method.

For example, here is a page fragment (called "chooser") that lets the user choose a number from 1 to 10:

< p > Choose a number from 1 to 10: < / p > < p > < t:count end= "10" value= "index" > < a t t:count id = "select" tburet type = "actionlink" context= "index" > ${index} < / t:comp > < / t:count > < / p >

The ActionLink component creates an action URL.

URL identifies the component ("chooser") that the page contains, the type of event (unless it is not the default and very common "action" event type), and the id ("select") of the component in the page with an additional context value.

An example of URL: http://localhost:8080/chooser.select/3.

When there are additional context values, they are appended to the path.

This demonstrates the key difference between Tapestry and the traditional URL, which is an action-oriented framework. The URL here does not mean what happens when the link is clicked, but rather identifies which component responds.

There is no simple mapping from URL to a piece of code; instead of sending notification events to Tapestry 5 component events, event handling methods are called. When the link generated by the component is clicked by the user, a Java method will be called.

@ OnEvent (component = "select") void valueChosen (int value) {_ value = value;}

Tapestry does two things here:

◆ confirms the valueChosen () method as the calling method.

◆ converts the context value from a string to an integer and passes it to the event handler.

In the above example, the valueChosen () method will be called (with at least one context value) when any event is generated by the choose component. Because the ActionLink component produces only a single event type, "action", this does not cause any problems (OnEvent can configure the event type).

Some components can generate multiple events, and sometimes you need more detailed parameters:

@ OnEvent (value = "action", component = "select") void valueChosen (int value) {_ value = value;}

The value property of OnEvent annotation is used to match the event name.

"action" is the default event type name, which is used by both ActionLink and Form components. If you omit the component parameter of OnEvent annotation, it receives all notification events that contain components, possibly including embedded components (because of the event bubbling mechanism event bubbling).

You can limit the events of which or which components you receive.

Event handling method naming convention

As an alternative to using annotations, we can name the event in a specified way, and the Tapestry 5 component event will call your method as if the method had been declared annotation.

This event handling method is named with the prefix "on", followed by the name of the action (with an uppercase capitalized), followed by "From" and an uppercase component id.

The previous example can be written as follows:

Void onActionFromSelect (int value) {_ value = value;}

If the event type is named "onAny", it will accept all event types, which we rarely need!

If for some inexplicable reason we need to receive the same events from different components in the same way, we need OnEvent annotation.

Tip from Howard: I find that I prefer naming conventions and keep annotation only for other inappropriate situations.

Event context (Event Context)

The context value (the context parameter of the ActionLink component) can be any object, however, only a simple string conversion occurs. Compared with Tapestry 4, he has a fine typing mechanism called "DataSqueezer".

In addition, no matter what the value is (string, number, date), it is converted to a text string. This will result in a more readable URL.

If there are multiple context values (by binding an object list or array to the context parameter of ActionLink), each value is sequentially appended to the URL.

When a Tapestry 5 component event handling method is called, a coercion conversion occurs from the string to the actual type. Event handling methods are called only if the number of context values is at least the same as the number of method parameters, and methods with too many parameters are skipped.

In addition, an event handling method can take a parameter of type java.lang.Object []. This parameter receives the entire contextual array. This is useful when the context is of different lengths at different times. We can use explicit parameters or individual parameters of type Object [].

Event bubbling (Event Bubbling)

The event bubbles up to the level until it is terminated. Event terminates when the event handling method returns a non-null value. For page navigation events, the return of the event handling method determines how the Tapestry will render the response.

This is the end of the article on "how to use Tapestry5 components". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, please share it for more people to see.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.