org.apache.tapestry5.corelib.components

## Class Form

- java.lang.Object
- - org.apache.tapestry5.corelib.components.Form

- All Implemented Interfaces:
    ClientElement, FormValidationControl

      @Events(value={"prepareForRender","prepare","prepareForSubmit","validate","submit","failure","success","canceled"})
       @SupportsInformalParameters
      public class Form
      extends Object
      implements ClientElement, FormValidationControl

  An HTML form, which will enclose other components to render out the various types of fields. A Form triggers many notification events. When it renders, it triggers a `EventConstants.PREPARE_FOR_RENDER` notification, followed by a `EventConstants.PREPARE` notification. When the form is submitted, the component triggers several notifications: first a `EventConstants.PREPARE_FOR_SUBMIT`, then a `EventConstants.PREPARE`: these allow the page to update its state as necessary to prepare for the form submission. The Form component then determines if the form was cancelled (see `SubmitMode.CANCEL`). If so, a `EventConstants.CANCELED` event is triggered. Next come notifications to contained components (or more accurately, the execution of stored `ComponentAction`s), to allow each component to retrieve and validate submitted values, and update server-side properties. This is based on the `t:formdata` query parameter, which contains serialized object data (generated when the form initially renders). Once the form data is processed, the next step is to trigger the `EventConstants.VALIDATE`, which allows for cross-form validation. After that, either a `EventConstants.SUCCESS` OR `EventConstants.FAILURE` event (depending on whether the `ValidationTracker` has recorded any errors). Lastly, a `EventConstants.SUBMIT` event, for any listeners that care only about form submission, regardless of success or failure. For all of these notifications, the event context is derived from the context component parameter. This context is encoded into the form's action URI (the parameter is not read when the form is submitted, instead the values encoded into the form are used). While rendering, or processing a Form submission, the Form component places a `FormSupport` object into the environment, so that enclosed components can coordinate with the Form component. It also places a `ValidationTracker` into the environment during both render and submission. During submission it also pushes a `Heartbeat` into the environment, which is `ended` just before deferred FormSupport operations are executed.
  See Also:
    `BeanEditForm`, `Errors`, `FormFragment`, `Label`

  Component Parameters
  Name | Type | Flags | Default | Default Prefix
  --- | --- | --- | --- | ---
  async | boolean | Since 5.4 |  | prop
  When true, the the form will submit as an asynchronous request (via XmlHttpRequest); the event handler methods can make use of the org.apache.tapestry5.services.ajax.AjaxResponseRenderer in order to force content updates to the client. This is used as an alternative to placing the form inside a org.apache.tapestry5.corelib.components.Zone and binding the `zone` parameter.
  autofocus | boolean |  |  | prop
  If true (the default), then the JavaScript will be added to position the cursor into the form. The field to receive focus is the first rendered field that is in error, or required, or present (in that order of priority).
  clientValidation | org.apache.tapestry5.corelib.ClientValidation | Not Null |  | literal
  Controls when client validation occurs on the client, if at all. Defaults to org.apache.tapestry5.corelib.ClientValidation#SUBMIT. org.apache.tapestry5.corelib.ClientValidation#BLUR was the default, prior to Tapestry 5.4, but is no longer supported.
  context | Object |  |  | prop
  The context for the link (optional parameter). This list of values will be converted into strings and included in the URI. The strings will be coerced back to whatever their values are and made available to event handler methods.
  secure | boolean |  |  | prop
  If true, then the Form's action will be secure (using an absolute URL with the HTTPs scheme) regardless of whether the containing page itself is secure or not. This parameter does nothing when (which is often the case in development mode). This only affects how the Form's action attribute is rendered, there is not (currently) a check that the form is actually submitted securely.
  validate | Object |  |  | prop
  Object to validate during the form submission process. The default is the Form component's container. This parameter should only be used in combination with the Bean Validation Library.
  validationId | String |  |  | prop
  Prefix value used when searching for validation messages and constraints. The default is the Form component's id. This is overridden by org.apache.tapestry5.corelib.components.BeanEditForm.
  zone | String |  |  | literal
  Binding the zone parameter will cause the form submission to be handled as an Ajax request that updates the indicated zone. Often a Form will update the same zone that contains it.

  Component Events
  Name | Description
  --- | ---
  canceled |
  failure |
  prepare |
  prepareForRender |
  prepareForSubmit |
  submit |
  success |
  validate |

  ### Form Control Element Components

    The following components are Tapestry wrappers around client-side HTML form elements:

    - Checkbox
    - DateField
    - Palette
    - PasswordField
    - Radio and RadioGroup
    - Select
    - Submit
    - TextArea
    - TextField

  ### Examples

    Examples of the Form component are provided in the many other pages that discuss specific form control element components, such as Radio andTextField.

  ### Notes

    The Form component generates a seemingly bewildering number of events, designed to address a wide range of needs. The goal is to give you as the developer the tools necessary to effeciently manage state.

    All of the events that are triggered will pass along the values defined by the context parameter. Most often, there is no context, or the context is a single value (a primary key used to identify the object being updated by the form).

    ### Render Events

    Render event handler methods should not return a value, doing so will be an error. The methods are intended to allow the page to convert a primary key stored in the context back into an object ready to have its properties updated by the Form.

    The context passed to component event handler methods is provided by reading the context parameter.

    - prepareForRender
    - prepare

    ### Submit Events

    Submit events may return a navigational value, which will abort any remaining processing of the form submission.

    The context provided to component event handler methods originates in the form submission (it is stored in hidden form fields); the context parameter is not read during a form submission.

    - prepareForSubmit
    - prepare
    - validate
    - failure or success
    - submit

    The validate event is to allow the page to perform cross-field validation. The validateForm event is a deprecated name for the validate event (it currently exists only for backwards compatibility). The failure or success event is fired based on whether there are or are not any validation errors.

    ### Form Ids

    It is considered a best practice to give explicit ids to Form components, and form control element components. These ids propagate down to the client side as element names and/or ids, and eventually show up as query parameters when the form is submitted.

    To achieve a more RESTful URL scheme, give the form component an id based on what it does rather than what data it updates, thus `<t:form t:id="search"/>` rather than `<t:form t:id="searchData"/>` or `<t:form t:id="searchForm"/>`.

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static String` | `FORM_DATA` Query parameter name storing form data (the serialized commands needed to process a form submission).
    `static StreamPageContent` | `STREAM_ACTIVE_PAGE_CONTENT`
    `static String` | `SUBMITTING_ELEMENT_ID` Used by `Submit`, etc., to identify which particular client-side element (by element id) was responsible for the submission.
    `protected ValidationTracker` | `tracker` The object which will record user input and validation errors.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `Form()`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods Deprecated Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected void` | `afterSuccessOrFailure()` A hook invoked from `onAction(org.apache.tapestry5.EventContext)` after the `EventConstants.SUBMIT` or `EventConstants.FAILURE` event has been triggered.
    `protected void` | `afterValidate()` A hook invoked from `onAction(org.apache.tapestry5.EventContext)` after the `EventConstants.VALIDATE` event has been triggered, and before the `tracker` has been cleared.
    `protected void` | `beforeProcessSubmit(EventContext context)` A hook invoked from `onAction(org.apache.tapestry5.EventContext)` before any other setup.
    `void` | `clearErrors()` Invokes `ValidationTracker.clear()`.
    `String` | `getClientId()` Forms use the same value for their name and their id attribute.
    `ValidationTracker` | `getDefaultTracker()` Returns an instance of `ValidationTrackerImpl`, lazily creating it as needed.
    `boolean` | `getHasErrors()` Returns true if the form's `ValidationTracker` contains any `errors`.
    `boolean` | `isValid()` Returns true if the form's `ValidationTracker` does not contain any `errors`.
    `void` | `recordError(Field field, String errorMessage)` A convenience method for invoking `ValidationTracker.recordError(Field, String)`.
    `void` | `recordError(String errorMessage)` A convenience method for invoking `ValidationTracker.recordError(String)`.
    `void` | `setDefaultTracker(ValidationTracker defaultTracker)` Deprecated. In 5.4; previously used only for testing

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### FORM_DATA

          public static final String FORM_DATA

      Query parameter name storing form data (the serialized commands needed to process a form submission).
      See Also:
        Constant Field Values

    - #### SUBMITTING_ELEMENT_ID

          public static final String SUBMITTING_ELEMENT_ID

      Used by `Submit`, etc., to identify which particular client-side element (by element id) was responsible for the submission. An empty hidden field is created, as needed, to store this value. Starting in Tapestry 5.3, this is a JSONArray with two values: the client id followed by the client name.
      Since:
        5.2.0
      See Also:
        Constant Field Values

    - #### STREAM_ACTIVE_PAGE_CONTENT

          public static final StreamPageContent STREAM_ACTIVE_PAGE_CONTENT

    - #### tracker

          @Parameter(value="defaultTracker")
          protected ValidationTracker tracker

      The object which will record user input and validation errors. When not using the default behavior supplied by the Form component (an immediate re-render of the active page when there are form validation errors), it is necessary to bind this parameter to a persistent value that can be maintained until the active page is re-rendered. See TAP5-1801.

  - ### Constructor Detail

    - #### Form

          public Form()

  - ### Method Detail

    - #### getDefaultTracker

          public ValidationTracker getDefaultTracker()

      Returns an instance of `ValidationTrackerImpl`, lazily creating it as needed. This property is the default for the tracker parameter; the property (as of Tapestry 5.4) is not persistent.
      Returns:
        per-request cached instance

    - #### setDefaultTracker

          public void setDefaultTracker(ValidationTracker defaultTracker)

      Deprecated. In 5.4; previously used only for testing

    - #### afterSuccessOrFailure

          protected void afterSuccessOrFailure()

      A hook invoked from `onAction(org.apache.tapestry5.EventContext)` after the `EventConstants.SUBMIT` or `EventConstants.FAILURE` event has been triggered. This method will be invoked regardless of whether the submit or failure event was aborted. This implementation does nothing.
      Since:
        5.4

    - #### beforeProcessSubmit

          protected void beforeProcessSubmit(EventContext context)

      A hook invoked from `onAction(org.apache.tapestry5.EventContext)` before any other setup. This implementation does nothing.
      Parameters:
        `context` - as passed to `onAction()`
      Since:
        5.4

    - #### afterValidate

          protected void afterValidate()

      A hook invoked from `onAction(org.apache.tapestry5.EventContext)` after the `EventConstants.VALIDATE` event has been triggered, and before the `tracker` has been cleared. Only invoked if the valiate event did not abort (that is, the no event handler method returned a value). This implementation does nothing.
      Since:
        5.4

    - #### recordError

          public void recordError(String errorMessage)

      Description copied from interface: `FormValidationControl`
      A convenience method for invoking `ValidationTracker.recordError(String)`.
      Specified by:
        `recordError` in interface `FormValidationControl`

    - #### recordError

          public void recordError(Field field,
                                  String errorMessage)

      Description copied from interface: `FormValidationControl`
      A convenience method for invoking `ValidationTracker.recordError(Field, String)`.
      Specified by:
        `recordError` in interface `FormValidationControl`

    - #### getHasErrors

          public boolean getHasErrors()

      Description copied from interface: `FormValidationControl`
      Returns true if the form's `ValidationTracker` contains any `errors`.
      Specified by:
        `getHasErrors` in interface `FormValidationControl`

    - #### isValid

          public boolean isValid()

      Description copied from interface: `FormValidationControl`
      Returns true if the form's `ValidationTracker` does not contain any `errors`.
      Specified by:
        `isValid` in interface `FormValidationControl`

    - #### clearErrors

          public void clearErrors()

      Description copied from interface: `FormValidationControl`
      Invokes `ValidationTracker.clear()`.
      Specified by:
        `clearErrors` in interface `FormValidationControl`

    - #### getClientId

          public String getClientId()

      Forms use the same value for their name and their id attribute.
      Specified by:
        `getClientId` in interface `ClientElement`

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