org.apache.tapestry5.internal.structure

## Interface Page

- All Superinterfaces:
    PageLifecycleCallbackHub
  All Known Implementing Classes:
    PageImpl

      public interface Page
      extends PageLifecycleCallbackHub

  Represents a unique page within the application. Pages are part of the internal structure of a Tapestry application; end developers who refer to "page" are really referring to the `root component` of the actual page.

  Starting in release 5.2, the nature of pages changed considerably. Pages are no longer pooled instances. Instead, pages are shared instances (per locale) but all internal mutable state is stored inside `PerthreadManager`. Page construction time is considered to extend past the page loaded callback. This is not quite perfect from a threading point-of-view (arguably, even write-once-read-many fields should be protected by synchronized blocks or other mechanisms). At best, we can be assured that the entire page construction phase is protected by a single synchronized block (but not on the page itself). An ideal system would build the page bottom to top so that all assignments could take place in constructors, assigning to final fields. Maybe some day.

  The Page object is never visible to end-user code, though it exposes an interface (`PageLifecycleCallbackHub` that is).

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Interface and Description
    --- | ---
    `static class` | `Page.Stats` Page construction statistics for the page.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `addLifecycleListener(PageLifecycleListener listener)` Deprecated. in 5.3.4; use `PageLifecycleCallbackHub.addPageLoadedCallback(Runnable)`, `PageLifecycleCallbackHub.addPageAttachedCallback(Runnable)`, or `PageLifecycleCallbackHub.addPageDetachedCallback(Runnable)` instead
    `void` | `addResetListener(PageResetListener listener)` Deprecated. in 5.3.4,
    `void` | `attached()` Invoked to inform the page that it is attached to the current request.
    `boolean` | `detached()` Invoked to inform the page that it is being detached from the current request.
    `void` | `discardPersistentFieldChanges()` Discards all persistent field changes for the page containing the component.
    `int` | `getAttachCount()` Returns the number of times the page has been attached to a request.
    `ComponentPageElement` | `getComponentElementByNestedId(String nestedId)` Retrieves a component element by its nested id (a sequence of simple ids, separated by dots).
    `Object` | `getFieldChange(String nestedId, String fieldName)` Gets a change for a field within the component.
    `org.slf4j.Logger` | `getLogger()` Returns the logger of the root component element.
    `String` | `getName()` Returns the short, logical name for the page.
    `Component` | `getRootComponent()` The root component of the page.
    `ComponentPageElement` | `getRootElement()` The root component of the page.
    `ComponentResourceSelector` | `getSelector()` The selector (which includes Locale) used when the page was constructor.
    `Page.Stats` | `getStats()` Returns the page construction statistics for this page.
    `boolean` | `hasResetListeners()` Returns true if there are any `PageResetListener` listeners.
    `boolean` | `isExactParameterCountMatch()` Returns true if extract parameter count matching is enabled.
    `void` | `loaded()` Inform the page that it is now completely loaded.
    `void` | `pageReset()` Invoked to notify `PageResetListener` listeners.
    `void` | `persistFieldChange(ComponentResources resources, String fieldName, Object newValue)` Posts a change to a persistent field.
    `void` | `removeLifecycleListener(PageLifecycleListener listener)` Deprecated. in 5.3.4, due to introduction of `PageLifecycleCallbackHub.addPageLoadedCallback(Runnable)`
    `void` | `setRootElement(ComponentPageElement component)` Invoked during page construction time to connect the page's root component to the page instance.
    `void` | `setStats(Page.Stats stats)` Invoked once at the end of page construction, to provide page construction statistics.

    - ### Methods inherited from interface org.apache.tapestry5.runtime.PageLifecycleCallbackHub

      `addPageAttachedCallback, addPageDetachedCallback, addPageLoadedCallback, addResetCallback, addVerifyCallback`

- - ### Method Detail

    - #### getName

          String getName()

      Returns the short, logical name for the page. This is the page name as it might included in an action or page render URL (though it will be converted to lower case when it is included).

    - #### getSelector

          ComponentResourceSelector getSelector()

      The selector (which includes Locale) used when the page was constructor.

    - #### setRootElement

          void setRootElement(ComponentPageElement component)

      Invoked during page construction time to connect the page's root component to the page instance.

    - #### getRootElement

          ComponentPageElement getRootElement()

      The root component of the page. This is the wrapper around the end developer's view of the page.

    - #### getRootComponent

          Component getRootComponent()

      The root component of the page. A convenience over invoking getRootElement().getComponent().

    - #### detached

          boolean detached()

      Invoked to inform the page that it is being detached from the current request. This occurs just before the page is returned to the page pool.

      A page may be clean or dirty. A page is dirty if its dirty count is greater than zero (meaning that, during the render of the page, some components did not fully render), or if any of its listeners throw an exception from containingPageDidDetach().

      The page pool should discard pages that are dirty, rather than store them into the pool.

      Under Tapestry 5.2 and pool-less pages, the result is ignored; all mutable state is expected to be discarded automatically from the `PerthreadManager`. A future release of Tapestry will likely convert this method to type void.
      Returns:
        true if the page is "dirty", false otherwise
      See Also:
        `PageLifecycleListener.containingPageDidDetach()`

    - #### attached

          void attached()

      Invoked to inform the page that it is attached to the current request. This occurs when a page is first referenced within a request. If the page was created from scratch for this request, the call to `loaded()` will preceded the call to `attached()`.

      First all listeners have `PageLifecycleListener.restoreStateBeforePageAttach()` invoked, followed by `PageLifecycleListener.containingPageDidAttach()`.

    - #### loaded

          void loaded()

      Inform the page that it is now completely loaded.
      See Also:
        `PageLifecycleListener.containingPageDidLoad()`

    - #### addLifecycleListener

          void addLifecycleListener(PageLifecycleListener listener)

      Deprecated. in 5.3.4; use `PageLifecycleCallbackHub.addPageLoadedCallback(Runnable)`, `PageLifecycleCallbackHub.addPageAttachedCallback(Runnable)`, or `PageLifecycleCallbackHub.addPageDetachedCallback(Runnable)` instead
      Adds a listener that is notified of large scale page events.

    - #### removeLifecycleListener

          void removeLifecycleListener(PageLifecycleListener listener)

      Deprecated. in 5.3.4, due to introduction of `PageLifecycleCallbackHub.addPageLoadedCallback(Runnable)`
      Removes a listener that was previously added.
      Since:
        5.2.0

    - #### getLogger

          org.slf4j.Logger getLogger()

      Returns the logger of the root component element. Any logging about page construction or activity should be sent to this logger.

    - #### getComponentElementByNestedId

          ComponentPageElement getComponentElementByNestedId(String nestedId)

      Retrieves a component element by its nested id (a sequence of simple ids, separated by dots). The individual names in the nested id are matched without regards to case. A nested id of '' (the empty string) returns the root element of the page.
      Throws:
        `UnknownValueException` - if the nestedId does not correspond to a component

    - #### persistFieldChange

          void persistFieldChange(ComponentResources resources,
                                String fieldName,
                                Object newValue)

      Posts a change to a persistent field.
      Parameters:
        `resources` - the component resources for the component or mixin containing the field whose value changed
        `fieldName` - the name of the field
        `newValue` - the new value for the field

    - #### getFieldChange

          Object getFieldChange(String nestedId,
                              String fieldName)

      Gets a change for a field within the component.
      Parameters:
        `nestedId` - the nested component id of the component containing the field
        `fieldName` - the name of the persistent field
      Returns:
        the value, or null if no value is stored

    - #### discardPersistentFieldChanges

          void discardPersistentFieldChanges()

      Discards all persistent field changes for the page containing the component. Changes are eliminated from persistent storage (such as the `Session`) which will take effect in the next request (the attached page instance is not affected).

    - #### addResetListener

          void addResetListener(PageResetListener listener)

      Deprecated. in 5.3.4,
      Adds a new listener for page reset events.
      Parameters:
        `listener` - will receive notifications when the page is accessed from a different page
      Since:
        5.2.0

    - #### hasResetListeners

          boolean hasResetListeners()

      Returns true if there are any `PageResetListener` listeners.
      Since:
        5.2.0

    - #### pageReset

          void pageReset()

      Invoked to notify `PageResetListener` listeners.

    - #### setStats

          void setStats(Page.Stats stats)

      Invoked once at the end of page construction, to provide page construction statistics.
      Since:
        5.3

    - #### getStats

          Page.Stats getStats()

      Returns the page construction statistics for this page.

    - #### getAttachCount

          int getAttachCount()

      Returns the number of times the page has been attached to a request. This is a rough measure of how important the page is, relative to other pages. This value is volatile, changing constantly.
      Since:
        5.3

    - #### isExactParameterCountMatch

          @NonVisual
          boolean isExactParameterCountMatch()

      Returns true if extract parameter count matching is enabled.
      Since:
        5.4
      See Also:
        `MetaDataConstants.UNKNOWN_ACTIVATION_CONTEXT_CHECK`

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