wffweb - Java Developers Guide

ParentGainedListener & ParentLostListener since wffweb-12.0.1

ParentGainedListener & ParentLostListener can be added on any tag. If a tag gains a parent or loses its parent by the framework (eg: whenURI event) then also the listeners will get invoked.

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ParentGainedListener

ParentGainedListener can be used to get an event when a tag gains a parent. When a ParentGainedListener is added using addParentGainedListener it will return an id of its internal slot, this id can be used to remove that listener from the tag using removeParentGainedListener method, see the following example.

						Div div1 = new Div(null);
Div div2 = new Div(null);

long listenerSlotId = div1.addParentGainedListener(event -> {
    System.out.println("addParentGainedListener invoked");
});

//this line will invoke addParentGainedListener
div2.appendChild(div1);

//this will remove the listener added to the tag
div1.removeParentGainedListener(listenerSlotId);

ParentLostListener

ParentLostListener can be used to get an event when a tag loses its parent. When a ParentLostListener is added using addParentLostListener it will return an id of its internal slot, this id can be used to remove that listener from the tag using removeParentLostListener method, see the following example.

						Div div1 = new Div(null);
Div div2 = new Div(null);
div2.appendChild(div1);

long listenerSlotId = div1.addParentLostListener(event -> {
    System.out.println("addParentLostListener invoked");
});

//this line will invoke addParentLostListener
div2.removeChild(div1); // or div2.removeAllChildren();

//this will remove the listener added to the tag
div1.removeParentLostListener(listenerSlotId);

Note: The listener slot id is NOT globally unique, it is unique only for the corresponding tag.

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