ZK Client-side Reference/Notifications/Client Activity Watches

In most cases, a widget or an application needs only to listen Event as described in the Client-side Event listening section. However, there are some activities not available as a DOM event (Event) or a ZK event (Event), such as when a widget is becoming invisible, or a window is brought to top. This kind of activity can be listened by so-called watch (zWatch)

Notice that application developers rarely need to access it. It is more for component development.

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Listen and Unlisten

To add a watch (i.e., listen to a client activity), you could use zWatch.listen(Map) as follows:

zWatch.listen({
    onSize: this,
    onShow: this,
    onHide: [this, this._onHide]
});

As shown, the key of each entry in the given map is the name of the client activity (aka., the watch name), and the value could be one of the following:

• An object that has a method with the same name. In the above case, this must have the onSize and onSHow methods
• A two-element array, where the first element is the target, and the second is the method

The signature of the method is as follows.

function onWhatever(ctl, arg0, arg1...) {
  //ctl.origin: the object passed as the first argument to zWatch.fire or zWatch.fireDown
  //ctl.fireDown(something) and ctl.fire(something):
  //   
}

where ctl is a controller allowing you to have better control of the invocation sequence of the listeners, and arg0 and others are the arguments that passed to zWatch.fire(String, Object, Map) or zWatch.fireDown(String, Object, Map).

The controller has two methods: fire and fireDown, and one field: origin. The fire and fireDown methods are used to fore the remaining listeners (caused by the same invocation of of zWatch.fire(String, Object, Map) or zWatch.fireDown(String, Object, Map)) to be invoked. If your listener doesn't call any of them, the other listeners are called in the same order of registration.

Here is the pseudo code for the controller:

interface Controller {
  /** Usually zk.Widget (unless fire and fireDown was called with a different object) */
  Object origin;
  /** enforce the remaining listeners to be invoked immediately (change the invocation sequence) */
  void fire(Object ref, Object...);
  /** enforce the remaining listeners to be invoked immediately (change the invocation sequence) */
  void fireDown(Object ref, Object...);
}

where ref is optional. If specified, it will invoke only the listeners for the given object (and its descendants if fireDown) that are not invoked yet. If null, it will invokes all the listeners that are not invoked yet.

The origin field (ctl.origin) is the original object (usually a widget, Widget) passed as the first argument when zWatch.fire(String, Object, Map) or zWatch.fireDown(String, Object, Map) was called. In other words, it is the one causes the client activity. It is null if not available.

To unlisten, you could use zWatch.unlisten(Map) as follows:

zWatch.unlisten({
    onSize: this,
    onShow: this,
    onHide: [this, this._onHide]
});

Fire

The client activity is triggered (aka., fired) by either zWatch.fire(String, Object, Map) or zWatch.fireDown(String, Object, Map).

zWatch.fire(String, Object, Map) will invoke the listeners for the target object (the first argument), while zWatch.fireDown(String, Object, Map) will invokes the listeners for the target object and all of its descendants (i.e., the target object's children, grandchildren...).

For example, if a widget resizes itself, it could fire down onSize as follows.

zWatch.fireDown("onSize", wgt);

The target object could be anything as long as the listener recognizes it, but we use Widget only.

Client Activities

Here is the list of client activities that you could watch.

beforeSize

Called right before the browser window or the parent widget is resized.

beforeSize and onSize are fired when the browser window or a widget is resized. beforeSize is fired first, such that the listener could reset style's width or height and the the listener of onSize can change it to the correct size. Notice that it is a must for the TD/TR tag. Otherwise, the onSize's listener cannot change its width/height correctly.

Notice zWatch's fireDown must be used to fire this event, so only the listeners of descendants of the specified widget will be called.

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