有几句代码看不懂，望解释下

[jsjysxw]

componentWillUnmount() { this.props.homeComponent.removeSubscriber(this.onSubscriber); }

onSubscriber = (preTab, currentTab)=> {
    var changedValues = this.props.homeComponent.changedValues;
    if (changedValues.my.themeChange && preTab.styles) {
        this.setState({
            theme: preTab
        })
        return;
    }
    if (currentTab != FLAG_TAB.flag_trendingTab)return;
    if (FLAG_TAB.flag_trendingTab === currentTab && changedValues.my.languageChange) {//从设置页面切换过来
        this.props.homeComponent.onReStart(FLAG_TAB.flag_trendingTab);
    }
}

this.onSubscriber调用的时候是不用传参吗？preTab ，和currentTab 的值是哪来呢，onSubscriber的值又是什么呢 新手问题，望谅解