Angular Component之间的事件通知机制

/**
 * Wraps an event listener with a function that marks ancestors dirty and prevents default behavior,
 * if applicable.
 *
 * @param {?} tNode The TNode associated with this listener
 * @param {?} lView The LView that contains this listener
 * @param {?} listenerFn The listener function to call
 * @param {?} wrapWithPreventDefault Whether or not to prevent default behavior
 * (the procedural renderer does this already, so in those cases, we should skip)
 * @return {?}
 */
function wrapListener(tNode, lView, listenerFn, wrapWithPreventDefault) {
    // Note: we are performing most of the work in the listener function itself
    // to optimize listener registration.
    return (/**
     * @param {?} e
     * @return {?}
     */
    function wrapListenerIn_markDirtyAndPreventDefault(e) {
        // Ivy uses `Function` as a special token that allows us to unwrap the function
        // so that it can be invoked programmatically by `DebugNode.triggerEventHandler`.
        if (e === Function) {
            return listenerFn;
        }
        // In order to be backwards compatible with View Engine, events on component host nodes
        // must also mark the component view itself dirty (i.e. the view that it owns).
        /** @type {?} */
        const startView = tNode.flags & 2 /* isComponentHost */ ?
            getComponentLViewByIndex(tNode.index, lView) :
            lView;
        // See interfaces/view.ts for more on LViewFlags.ManualOnPush
        if ((lView[FLAGS] & 32 /* ManualOnPush */) === 0) {
            markViewDirty(startView);
        }
        /** @type {?} */
        let result = executeListenerWithErrorHandling(lView, listenerFn, e);
        // A just-invoked listener function might have coalesced listeners so we need to check for
        // their presence and invoke as needed.
        /** @type {?} */
        let nextListenerFn = ((/** @type {?} */ (wrapListenerIn_markDirtyAndPreventDefault))).__ngNextListenerFn__;
        while (nextListenerFn) {
            // We should prevent default if any of the listeners explicitly return false
            result = executeListenerWithErrorHandling(lView, nextListenerFn, e) && result;
            nextListenerFn = ((/** @type {?} */ (nextListenerFn))).__ngNextListenerFn__;
        }
        if (wrapWithPreventDefault && result === false) {
            e.preventDefault();
            // Necessary for legacy browsers that don't support preventDefault (e.g. IE)
            e.returnValue = false;
        }
        return result;
    });
}