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WOComponent

Inherits from: WOElement NSObject

Implements: WOActionResults, EOKeyValueCoding (com.apple.yellow.eocontrol), EOKeyValueCodingAdditions (com.apple.yellow.eocontrol)

Package: com.apple.yellow.webobjects

Class Description

WOComponent objects dynamically render web pages (or sections of pages) at run time. They provide custom navigation and other logic for the page, provide a framework for organizing constituent objects (static and dynamic HTML elements and subcomponents), and enable the attribute bindings of dynamic elements.

The WOComponent class has many methods that have the same names as methods of the WOApplication class. However, the scope of the WOComponent methods is limited to a component rather than being application-wide. For example, you can control component-definition caching on a per-component basis using setCachingEnabled, which has a WOApplication counterpart. When this kind of caching is enabled for a component, the application parses the contents of the component directory the first time the component is requested, creates the component definition, stores this object in memory, and restores it for subsequent requests.

WOComponent objects also respond to awake, sleep, and the three request-handling messages: takeValuesFromRequest, invokeActionForRequest,and appendToResponse. You can override these methods in your compiled subclasses, and thereby integrate your custom behavior into the request-response loop. (You can also override these methods in component scripts using WebScript.)

Subcomponents

A WOComponent object can represent a dynamic fragment of a Web page as well as an entire page. Such subcomponents, or reusable components, are nested within a parent component representing the page or another subcomponent. Each component keeps track of its parent and subcomponents-when a component receives a request-handling message, such as takeValuesFromRequest, it forwards that message to its subcomponents

The WOComponent class also provides a child-parent callback mechanism to allow a child component to communicate with its parent. In the parent's declaration file, bind an arbitrary attribute of the child to an action method of the parent. Then, as the last step in the child's action method, invoke performParentAction with the argument being the arbitrary attribute, returning the object received back as the response page. See the method description for performParentAction for details.

Stateless Components

For extra efficiency, you can create stateless components: components that can be shared between sessions. Stateless components aren't replicated each time they're needed; rather, a single shared instance is referenced each time the component is used.

Stateless components cannot have state. They can have instance variables, but the variable's content must be transient. To ensure that when the shared instance of a component is reused by another session there are no side effects, reset your component's instance variables by implementing the reset method. In your implementation of reset , release and set to null each instance variable. Note that a stateless component's instance variables will remain valid for the duration of the phase (takeValuesFromRequest, invokeAction and appendToResponse); this lets you use instance variables in your stateless components to hold things analgous to items in a WORepetition.

Stateless components primarily save memory, but they can significantly speed up your application as well depending on how many stateless components you use in your application. To make a component stateless, override the component's isStateless method so that it returns true.

If a stateless component is needed simultaneously in separate threads, additional instances of the component are created (and later discarded) as necessary to prevent conflicts. Thus, the number of threads in which a component could be used determines the maximum number of instances of a stateless component that may be allocated at any given time.

Interfaces Implemented

WOActionResults
generateResponse
EOKeyValueCoding
handleQueryWithUnboundKey

handleTakeValueForUnboundKey

storedValueForKey

takeStoredValueForKey

takeValueForKey

unableToSetNullForKey

valueForKey
EOKeyValueCoding
takeValueForKeyPath

takeValuesFromDictionary

valueForKeyPath

valuesForKeys

Method Types

Creation

WOComponent

Obtaining attributes

application

baseURL

context

frameworkName

hasSession

name

pageWithName

path

session

Caching

isCachingEnabled

setCachingEnabled

Handling requests

appendToResponse

awake

ensureAwakeInContext

invokeActionForRequest

sleep

takeValuesFromRequest

Logging

debugString

isEventLoggingEnabled

logString

Template parsing

templateWithHTMLString:declarationString:languages:

Component statistics

descriptionForResponse

Invoking actions

parent

performParentAction

Synchronizing components

canGetValueForBinding

canSetValueForBinding

hasBinding

setValueForBinding

synchronizesVariablesWithBindings

valueForBinding

Other

isStateless

reset

templateWithName

validateTakeValueForKeyPath

Constructors

WOComponent

public WOComponent()

WebObjects Builder archive file exists in the component directory, it initializes component variables from this archive. This constructor throws exceptions if it cannot determine the name of the component or if it cannot initialize the object for any other reason. Override WOComponent() in compiled subclasses to perform custom initializations; as always, invoke super's default constructor as the first thing.

Static Methods

debugString

public static void debugString(String aString)

Like logString, prints a message to the standard error device (stderr), but only prints the message if the WODebuggingEnabled user default option is true. If WODebuggingEnabled is false, the debugString messages aren't printed. See logString for information on the format of aString.

logString

public static void logString(String aString)

Prints a message to the standard error device (stderr). The message can include formatted variable data using String's concatenation feature, for example:

int i = 500;

float f = 2.045;

WOComponent.logString("Amount = " + i + ", Rate = " + f ", Total = " + i*f);

templateWithHTMLString:declarationString:languages:

public static WOElement templateWithHTMLString( String anHTMLString, String aDeclarationString, NSArray languages)

Programmatically creates the component's template using anHTMLString as the HTML template contents and aDeclarationString as the declarations file contents. Returns (as a WOElement object) the graph of static and dynamic elements build by parsing the HTML and declaration strings. You can then use the returned WOElement as the component's template.

See Also: templateWithName

Instance Methods

appendToResponse

public void appendToResponse( WOResponse aResponse, WOContext aContext)

Component objects associated with a response receive this message during the last phase of the request-response loop. In the append-to-response phase, the application objects (particularly the response page instance itself) generate the HTML content of the page. WOComponent's default implementation of this method forwards the message to the root WOElement object of the component template. Compiled or scripted subclasses of WOComponent can override this method to replace or supplement the default behavior with custom logic.

application

public WOApplication application()

Returns the WOApplication object for the current application.

See Also: WOApplication class, context, session

awake

public void awake()

Invoked at the beginning of a WOComponent's involvement in a cycle of the request-response loop, giving the WOComponent an opportunity to initialize its instance variables or perform setup operations. The default implementation does nothing.

See Also: ensureAwakeInContext, sleep

baseURL

public String baseURL()

Returns the component URL relative to the server's document root, for example: "/WebObjects/MyApp.woa/Resources/Main.wo"

See Also: name, path

canGetValueForBinding

public boolean canGetValueForBinding(String aBindingName)

Verifies that the binding exists and that valueForBinding will return a value.

canSetValueForBinding

public boolean canSetValueForBinding(String aBindingName)

Verifies that the binding exists and that setValueForBinding will succeed.

context

public WOContext context()

Returns the WOContext object for the current transaction.

See Also: WOContext class, application, session

descriptionForResponse

public String descriptionForResponse( WOResponse aResponse, WOContext aContext)

Records information about the component if it is the response component in the current request-response loop transaction. The default implementation records the component's name. You might override this method if you want to record more information about the component. For example, you might want to record the values of some instance variables as well as the component name.

This message is sent only to the top-level response component, that is, the one representing the entire page. Components nested inside of that top-level component do not receive this message.

If a CLFF log file is kept for this application, the string returned by this method is recorded in that log file. Thus, you must ensure that the string you return can be analyzed by a CLFF-analysis tool.

See Also: WOStatisticsStore class

ensureAwakeInContext

public void ensureAwakeInContext(WOContext aContext)

Ensures that the receiver is awake in the specified context. Invoke this method before using a component which was stored in a variable. You don't need to invoke ensureAwakeInContext if the component was just created with pageWithName, if it was restored from the WebObjects page cache, or if the page will simply be returned as the result of an action. That is, you only need to invoke this method if you're going to send messages to a component that is otherwise not awakened. If the receiving component is already awake, this method has no effect.

See Also: awake

frameworkName

public String frameworkName()

If the component is stored in a framework, this method returns the name of that framework. For example, if the component is in the framework NeXT_ROOT/System/Library/Frameworks/WOExtensions.framework, then this method returns the string "WOExtensions".

If the component is not stored in a framework, this method returns null.

See Also: WOResourceManager class

generateResponse

public abstract WOResponse generateResponse()

Returns a newly-created WOResponse object. WOComponent's implementation of this method translates the receiving component into a WOResponse object by sending iteself an appendToResponse message.

See Also: generateResponse (WOResponse)

hasBinding

public boolean hasBinding(String aBindingName)

Returns whether the component has a binding named aBindingName. This method traverses the chain of associations to the top-level parent, if necessary.

hasSession

public boolean hasSession()

Returns whether the component is already in a session. For example, in direct actions, sessions are lazily created and you can avoid creating another one unnecessarily by calling hasSession before session.

See Also: session

invokeActionForRequest

public WOElement invokeAction( WORequest aRequest, WOContext aContext)

WOComponent objects associated with a request page receive this message during the middle phase of request handling. In this middle phase, the invokeActionForRequest message is propagated through the WOElement objects of the page; the dynamic element on which the user has acted (by, for example, clicking a button) responds by triggering the method in the request component that is bound to the action. WOComponent's default implementation of this method forwards the message to the root WOElement object of the component template.Compiled or scripted subclasses of WOComponent can override this method to replace or supplement the default behavior with custom logic. (Scripted subclasses must use the Objective-C form of this method: invokeActionForRequest:inContext:).

See Also: appendToResponse, takeValuesFromRequest

isCachingEnabled

public boolean isCachingEnabled()

Returns whether component-definition caching is enabled for this component. false is the default.

See Also: setCachingEnabled

isEventLoggingEnabled

public boolean isEventLoggingEnabled()

Called to determine if a component wants event logging. This is not desirable, for example, for components which are associated with event display as they would interfere with the actual event logging. The default implementation of this method returns true.

See Also: WOEvent class

isStateless

public boolean isStateless()

By default, this method returns false, indicating that state will be maintained for instances of the receiver. Overriding this method to return true will make the component stateless. A single instance of each stateless component is shared between multiple sessions, reducing your application's memory footprint.

See Also: reset

name

public String name()

Returns the name of the component, which includes a path of all directories under DOCUMENTROOT/WebObjects and is minus the ".wo" extension; for example "Main" is a typical component name.

See Also: baseURL, path

pageWithName

public WOComponent pageWithName(String aName)

Returns a new page instance (a WOComponent object) identified by aName. If aName is null, the "Main" component is assumed. If the method cannot create a valid page instance, it throws an exception.

See Also: restorePageForContextID (WOSession), savePage (WOSession)

parent

public WOComponent parent()

Returns the parent component of the receiver.

path

public String path()

Returns the file-system path of the component, which is an absolute path and includes the ".wo" extension; for example "C:\Apple\Library\WOApps\MyApp.woa\Resources\Main.wo" is a typical path.

See Also: baseURL, name

performParentAction

public Object performParentAction(String anActionName)

Allows a subcomponent to invoke an action method of its parent component bound to the child component (attribute). Parent and child components are "synchronized" when this method returns: the variables that are bound by a declaration of the child component in the parent component's declaration file have the same value.

An example best illustrates this mechanism. Let's say you have a Palette subcomponent, and this WOComponent is nested in a parent component with a "displaySelection" action method. When the user selects an item in the palette (perhaps a color), you want to invoke "displaySelection" to show the result of the new selection (perhaps a car in the new color). The declaration in the parent's ".wod" file would look like this:

PALETTE: Palette {
   selection = number;
   callBack = "displaySelection";
};

The "callBack" item is an arbitrary attribute of the child component bound in this declaration to the parent component's "displaySelection" method.The performParentAction method is used to activate this binding. Let's assume the child component has an action method called "click"; the implementation would look like this:

public WOComponent click() {             /* this is the child's action */
    selection = /* some value */;
    /* now invoke the parent's action */
    return performParentAction(callBack);
}

reset

public void reset()

This method-which is only invoked if the component is stateless-allows a component instance to reset or delete temporary references to objects that are specific to a given context. To ensure that when the shared instance of a component is reused by another session there are no side effects, implement this method so that it releases and sets to null each of the component's instance variables.

See Also: isStateless

session

public WOSession session()

Returns the current WOSession object. This method creates a new one if there isn't one.

See Also: WOSession class, application, context, hasSession

setCachingEnabled

public void setCachingEnabled(boolean flag)

Enables or disables the caching of component definitions for the receiving component. WOComponent definitions contain templates and other common information related to components, and are used to generate instances of those components.When this attribute is set to true, the application parses the HTML template and the declaration (".wod") file of a component once and then stores the resulting component definition for future requests. By default, this kind of caching is disabled so that you can edit a scripted component without having to relaunch the application every time to check the results.(Note that this does not apply to Java subclasses of WOComponent; in this case, you still have to kill and relaunch the application.)

With WOApplication's method of the same name, you can turn component-definition caching off globally. You can then control caching of individual component definitions using WOComponent's version of this method. Selective caching is an especially valuable technique for very large applications where only the most frequently requested components should be cached.

See Also: isCachingEnabled

setValueForBinding

public void setValueForBinding( Object aValue, String aBindingName)

Sets the value of the binding specified by aBindingName in the parent component to aValue. If the binding isn't settable, this method throws an exceptionn.

See Also: isValueSettableInComponent ( WOAssociation class)

sleep

public void sleep()

Invoked at the conclusion of a request-handling cycle to give component the opportunity for deallocating objects created and initialized in its awake method. The default implementation does nothing.

synchronizesVariablesWithBindings

public boolean synchronizesVariablesWithBindings()

Returns whether a nested component pulls all values down from its parent and pushes all values to its parent before and after each phase of the request-response loop. By default, this method returns true. Override this method to create a non-synchronizing component.

See Also: setValueForBinding, valueForBinding

takeValuesFromRequest

public void takeValuesFromRequest( WORequest aRequest, WOContext aContext)

WOComponent objects associated with a request receive this message during the first phase of the request-response loop. The default WOComponent behavior is to send the message to the root object of the component's template.In this phase, each dynamic element in the template extracts any entered data or changed state (such as a check in a check box) associated with an attribute and assigns the value to the component variable bound to the attribute.Compiled or scripted subclasses of Component can override this method to replace or supplement the default behavior with custom logic. (Scripted subclasses must use the Objective-C form of this method: takeValuesFromRequest:inContext:).

templateWithName

public WOElement templateWithName(String aName)

Returns the root object of the graph of static and dynamic HTML elements and subcomponents that is used to graphically render the component identified by aName. This template is constructed from the ".html" and ".wod" file found in the component directory. You identify the template by specifying the component name: for example, "HelloWorld." If the template is not cached, the application will parse the HTML and declaration files of the specified component to create the template.

See Also: setCachingEnabled

validationFailedWithException

public void validationFailedWithException( Throwable exception, Object value, String keyPath)

Called when an Enterprise Object or formatter failed validation during an assignment. The default implementation ignores the error. Subclassers can override to record the error and possibly return a different page for the current action.

validateTakeValueForKeyPath

public Object validateTakeValueForKeyPath(Object value, String keyPath) throws com.apple.yellow.eocontrol.EOValidation.Exception

Validates (and coerces) the given value, assigning it if it is different than the current value. Throws a validation exception if validateValueForKey returns an exception. Returns the coerced (assigned) value.

valueForBinding

public Object valueForBinding(String aBindingName)

Gets the value for the specified binding from the parent component. If the parent doesn't provide aBindingName in its delcarations file, this method attempts to get the value from the current component using valueForKey. If the current component doesn't define this key, this method returns null. This cascading lookup makes it easy to provide default values for optional bindings.