react异常：Can't perform a React state update on an unmounted component

Warning: Can't perform a React state update on an unmounted component.
This is a no-op, but it indicates a memory leak in your application.
To fix, cancel all subscriptions and asynchronous tasks in the componentWillUnmount method.

原因：
react组件已经被销毁，而此时我们的异步操作（通常为调用接口更改state操作）还未结束。当我们的异步执行完成后要执行setState操作时，已经无法获得组件信息，由此造成该异常！

解决方案：
我们应该在组件中通过componentWillUnmount钩子函数在组件销毁的时候将异步方法撤销：

componentWillUnmount() {
    this.setState = ()=>false;
}