我有以下功能:
onSelectDepartment = (evt) => {
const department = evt.target.value;
const course = null;
this.setState({ department, course });
this.props.onChange({ name: 'department', value: department });
this.props.onChange({ name: 'course', value: course });
if (department) this.fetch(department);
};
问题是，setState函数调用后，组件上的render函数是立即执行还是函数调用结束后执行？
最佳答案
render function on the component will be executed immediately or after function call is finished?
没有人能保证渲染函数何时会被调用，因为 setState 是异步的，当我们调用 setState 时意味着我们要求 React 使用新的状态值更新 ui(请求调用渲染方法)，但确切地说什么时候会发生，我们永远不知道。
看看是什么react doc says about setState :
setState() enqueues changes to the component state and tells React that this component and its children need to be re-rendered with the updated state. This is the primary method you use to update the user interface in response to event handlers and server responses.
Think of setState() as a request rather than an immediate command to update the component. For better perceived performance, React may delay it, and then update several components in a single pass. React does not guarantee that the state changes are applied immediately.
查看此答案以获取有关 setState 的异步行为的更多详细信息:Why calling setState method doesn't mutate the state immediately?
关于javascript - render 会在 setState 之后立即被调用吗？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/48880548/