com.smartgwt.client.util

## Class EventHandler

- java.lang.Object
- - com.smartgwt.client.util.EventHandler

-     public class EventHandler
      extends java.lang.Object

  The ISC system provides a predictable cross-browser event-handling mechanism for ISC widgets. Events can be handled both at the page level (i.e., globally), and at the level of individual widgets.

  With the exception of a few page-specific events ('load', 'unload', 'idle' and 'resize'), events are processed in the following sequence:

  1. The event is sent to any global (page-level) event handlers. These handlers can cancel further propagation of the event by returning false. You can register to listen for any of the events linked in the seeAlso section (below) by calling `Page.setEvent` method.

  2. If the event occurred on a form element or a link, it is passed on to the browser so that the element will perform its default action. No widget receives the event.

  3. If the event occurred on an enabled widget (but not on a form element or link inside the widget), it is sent to that widget's event handler, if any. This handler can cancel further propagation of the event by returning false. An "enabled" widget is any widget that defines an event handler for one of the supported events. Interceptable events are defined in the "widgetEvents" section of Canvas.

  4. The event is "bubbled" up to the widget's parent in the containment hierarchy, if any. Again, the parent's handler for the event can cancel further propagation by returning false. This step is repeated, with the event "bubbling" up through the containment hierarchy, until a top-level widget is reached or the event is explicitly canceled. In brief, the ISC event model offers the best features of browser event models:

  - Page-first event handling allows you to reliably process or cancel any event before it affects the objects on the page.
  - Event "bubbling" ensures that parent widgets receive events sent to their children, and allows you to create generalized parent-level handlers rather than duplicating code in each child.
  Note: Canceling propagation of an event may cancel its side effects as well, including the generation of other (synthetic) events. For example, if a global mouseDown handler returns false, drag-and-drop events will not be generated. Specific effects are discussed in the descriptions of the various events in the following sections.

  Smart GWT libraries will not interfere with native event handling when events occur outside of a target widget. You can therefore have HTML that is not ISC-based on the same page as widget objects that will react to native events as you would expect.

  You can use isc.Event as an alias for isc.EventHandler.

  See Also:
    `PageEvent`, `com.smartgwt.client.util.Page#setEvent`, `com.smartgwt.client.util.Page#clearEvent`

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `EventHandler()`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `static java.lang.Boolean` | `altKeyDown()` Return true if the alt (option) key is being held down.
    `static java.lang.Boolean` | `ctrlKeyDown()` Return true if the control key is being held down.
    `static Rectangle` | `getDragRect()` During a drag with dragAppearance of either "target" or "outline", returns the page-relative coordinates of whatever element is being dragged.
    `static Canvas` | `getDragTarget()` Returns the current dragTarget.
    `static java.lang.String` | `getKey()` Return the name of the key for the event passed in.
    `static java.lang.String` | `getKeyEventCharacter()` Return the character for the current key being pressed.
    `static int` | `getKeyEventCharacterValue()` Returns the numeric characterValue reported by the browser.
    `static java.lang.Integer` | `getMouseDownX()` Return the page-relative X (horizontal) coordinate of an event.
    `static java.lang.Integer` | `getMouseDownY()` Return the page-relative Y (vertical) coordinate of an event.
    `static com.google.gwt.user.client.Element` | `getNativeMouseTarget()` Returns the natively reported target (or source) DOM element for the current mouse event.
    `static Canvas` | `getTarget()` Return the canvas that is the target of the mouse event.
    `static float` | `getWheelDelta()` Applies to `mouseWheel` events only.
    `static double` | `getWheelDeltaAsDouble()` Applies to `mouseWheel` events only.
    `static int` | `getX()` Return the page-relative X (horizontal) coordinate of an event.
    `static int` | `getY()` Return the page-relative Y (vertical) coordinate of an event.
    `static java.lang.Boolean` | `leftButtonDown()` Returns true if the left mouse button is being pressed.
    `static java.lang.Boolean` | `rightButtonDown()` Returns true if the right mouse button is being pressed.
    `static void` | `setDragTracker(java.lang.String html)` Set the HTML for the drag tracker that follows the mouse during a drag and drop interaction.
    `static void` | `setDragTracker(java.lang.String html, int newWidth, int newHeight, int offsetX, int offsetY)` Set the HTML for the drag tracker that follows the mouse during a drag and drop interaction.
    `static java.lang.Boolean` | `shiftKeyDown()` Return true if the shift key is being held down.
    `static java.lang.Boolean` | `targetIsMasked(Canvas target)` Return whether this Canvas is masked by a clickMask (see `Canvas.showClickMask`).

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

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

- - ### Constructor Detail

    - #### EventHandler

          public EventHandler()

  - ### Method Detail

    - #### altKeyDown

          public static java.lang.Boolean altKeyDown()

      Return true if the alt (option) key is being held down. Note that this is only set reliably for keyboard events.
      Returns:
        true == alt key is down

    - #### ctrlKeyDown

          public static java.lang.Boolean ctrlKeyDown()

      Return true if the control key is being held down. Note that this is only set reliably for keyboard events.
      Returns:
        true == control key is down

    - #### getDragTarget

          public static Canvas getDragTarget()

      Returns the current dragTarget. This is the component on which the drag and drop interaction was initiated. This only returns something meaningful during a drag and drop interaction.
      Returns:
        The dragTarget.
      See Also:
        `Canvas.getDragTarget()`

    - #### getKeyEventCharacter

          public static java.lang.String getKeyEventCharacter()

      Return the character for the current key being pressed. Note that this is only set reliably for keyPress events on character keys.
      Returns:
        Character the user entered. May be null for non-character keys.

    - #### getKeyEventCharacterValue

          public static int getKeyEventCharacterValue()

      Returns the numeric characterValue reported by the browser. Only available on keyPress events, and only for character (or ascii control) keys
      Returns:
        Numeric character value reported by the browser (ASCII value of the key pressed)

    - #### getNativeMouseTarget

          public static com.google.gwt.user.client.Element getNativeMouseTarget()

      Returns the natively reported target (or source) DOM element for the current mouse event. NOTE: Smart GWT cannot guarantee that the same element will be reported in all browser/platform configurations for all event types. If you wish to make use of this value, we recommend testing your use case in all target browser configurations.
      Returns:
        native DOM element over which the mouse event occurred

    - #### getWheelDelta

          public static float getWheelDelta()

      Applies to `mouseWheel` events only. Returns a numeric value indicating how far the mouse wheel was rotated. This value will be positive if the user scrolled the mousewheel forward or up, or negative if scrolled in the other direction. For a standard wheel-mouse, an increment of 1 relates to the smallest possible rotation of the mouse wheel. For other scrolling devices, such as scroll gestures on a track pad, wheel delta may be reported in finer grained increments (causing this method to return a fractional value). Developers should also be aware that some browsers and operating systems allow the user to configure the sensitivity of the mouse wheel, which may change this value.
      Returns:
        numeric value indicating how far the mouse wheel was rotated.

    - #### getWheelDeltaAsDouble

          public static double getWheelDeltaAsDouble()

      Applies to `mouseWheel` events only. Returns a numeric value indicating how far the mouse wheel was rotated. This value will be positive if the user scrolled the mousewheel forward or up, or negative if scrolled in the other direction. For a standard wheel-mouse, an increment of 1 relates to the smallest possible rotation of the mouse wheel. For other scrolling devices, such as scroll gestures on a track pad, wheel delta may be reported in finer grained increments (causing this method to return a fractional value). Developers should also be aware that some browsers and operating systems allow the user to configure the sensitivity of the mouse wheel, which may change this value.
      Returns:
        numeric value indicating how far the mouse wheel was rotated.

    - #### getX

          public static int getX()

      Return the page-relative X (horizontal) coordinate of an event.
      Returns:
        x-coordinate in page coordinate space

    - #### getY

          public static int getY()

      Return the page-relative Y (vertical) coordinate of an event.
      Returns:
        y-coordinate in page coordinate space

    - #### leftButtonDown

          public static java.lang.Boolean leftButtonDown()

      Returns true if the left mouse button is being pressed.
      Returns:
        true == left button is down, false == up

    - #### rightButtonDown

          public static java.lang.Boolean rightButtonDown()

      Returns true if the right mouse button is being pressed.
      Returns:
        true == right button is down, false == up

    - #### shiftKeyDown

          public static java.lang.Boolean shiftKeyDown()

      Return true if the shift key is being held down. Note that this is only set reliably for keyboard events.
      Returns:
        true == shift key is down

    - #### targetIsMasked

          public static java.lang.Boolean targetIsMasked(Canvas target)

      Return whether this Canvas is masked by a clickMask (see `Canvas.showClickMask`).
      Parameters:
        `target` - widget to check
      Returns:
        true if masked, false if not masked.

    - #### setDragTracker

          public static void setDragTracker(java.lang.String html)

      Set the HTML for the drag tracker that follows the mouse during a drag and drop interaction.

      Your canvas can use this routine to set the drag tracker to whatever HTML you want like so:

              dragStart : function
           () {        isc.EventHandler.setDragTracker('Your contents here');    }

      Parameters:
        `html` - HTML for the tracker

    - #### setDragTracker

          public static void setDragTracker(java.lang.String html,
                            int newWidth,
                            int newHeight,
                            int offsetX,
                            int offsetY)

      Set the HTML for the drag tracker that follows the mouse during a drag and drop interaction.

      Your canvas can use this routine to set the drag tracker to whatever HTML you want like so:

              dragStart : function
           () {        isc.EventHandler.setDragTracker('Your contents here');    }

      Parameters:
        `html` - HTML for the tracker
        `newWidth` - new width for the tracker
        `newHeight` - new height for the tracker
        `offsetX` - x-offset for the tracker
        `offsetY` - y-offset for the tracker

    - #### getDragRect

          public static Rectangle getDragRect()

      During a drag with dragAppearance of either "target" or "outline", returns the page-relative coordinates of whatever element is being dragged. Calling this method allows you to write drag and drop logic that works identically even if dragAppearance is subsequently changed.
      Returns:
        lobal (page-relative) coordinates and size of the dragged element, as a 4-element array [left,top,width,height], or null if not dragging

    - #### getMouseDownX

          public static java.lang.Integer getMouseDownX()

      Return the page-relative X (horizontal) coordinate of an event.
      Returns:
        x-coordinate in page coordinate space

    - #### getMouseDownY

          public static java.lang.Integer getMouseDownY()

      Return the page-relative Y (vertical) coordinate of an event.
      Returns:
        y-coordinate in page coordinate space

    - #### getKey

          public static java.lang.String getKey()

      Return the name of the key for the event passed in. Note that this is only set reliably for keyboard events.

           Strings to identify the various keys on the keyboard.

           For alpha keys, the single (uppercase) character value is used, such as "Q"
           For Numeric keys, the number is used as in a single character string, like "1"
           Function keys are identified as "f1" - "f12"
           Non alpha-numeric character keys (such as the key for "[" / "{") are identified by their unmodified character value (the value obtained by hitting the key without holding shift down), by default - exceptions are listed below.
           Additional key names:
           - Space
           - Tab
           - Enter
           - Escape
           - Backspace
           - Insert
           - Delete
           - Arrow_Up
           - Arrow_Down
           - Arrow_Left
           - Arrow_Right
           - Home
           - End
           - Page_Up
           - Page_Down
           - Shift
           - Ctrl
           - Alt
           [Note: Some keys may not be available for capture on every platform]

      Returns:
        the key name
      See Also:
        `KeyNames`

    - #### getTarget

          public static Canvas getTarget()

      Return the canvas that is the target of the mouse event. Returns null if no canvas found.
      Returns:
        event target canvas