ref

The code below is a minimal working example to explain my problem. This code generates 3 Note components using Array.map and when you hit enter in them it empties the statically generated Note component above them using a ref to its DOM element. What I want to do is instead have the Note you hit enter in empty itself. I think this would require generating a dynamic array containing {id, ref} for each Note, so I could pass the Note id to handleKeyDown then search the refs array for that id and use the corresponding ref to change the DOM element. But I'm having trouble figuring out how to

boost中有一个bind库， 可以说是一个最为实用的tools了， 但是它与boost结合的有些紧密，而且其中的一些功能并不是很常用，就算将它bcp出独立的库也是一个不小的负担。如果在你的项目中不打算有boost库的痕迹但是又想使用bind的强大功能，那就来看看它吧。 一个一个超小型的bind库， 它实现了大部分boost::bind的功能， 只是将名字空间由boost 变换为 bi 。如果使用了一般的使用中通常可以将 boost::bind(my_fun(), _1,_2)(234, "hello world"); //形式替换为 bi::bind(my_fun(), _1, _2)(234, "hello world"); 既可完成编译，如果使用了名字空间，那就只需要将 using namespace boost 替换为 using namespafce bi 即可完成转化。 同boost::bind一样，它支持任意的函数对象，函数，函数指针，和成员函数指针，它还能将任何参数绑定为一个特定的值，或者将输入的参数发送到任意的位置。 从使用者方向看只是将bind 从boost名字空间移动到了 bi名字空间， 如果使用了 using namespace boost;的方式引入的boost::bind, 那么你很幸运！只要改成using namespace bi;就完成了。

I have a requirement to show thumbnails of videos(cards) in several rows and focus on the very first thumbnail. I did the display using Nested Map. The code basically iterates over a videos array and returns videos in several rows. How do we focus on the first element that renders? I think we need to get ref of the first element to focus. But how do we set ref here and reference it in another function? const CategoryGrid = props => { return ( <HotKeys handlers={handlers}> <div className="grid-container"> <p className="title"> {props.title.toUpperCase()} </p> <div className="grid"> { props

I'm writing a component that handle some internal state according to a ref of it's child (a mouse event related to that child's ref for example). This component is using a render-prop to pass on the relevant piece of state to it's child, and render the child with the ref attached via React.cloneElement util. The problem is that when the child is a class component, for some reason the ref is not available, and i can't find a way to render it as it's a react element object with a type of function (after i clone it of course). But if the child is just a DOM node like a div for example, it is

I face the following problem: I need many subsets of a big matrix. Actually I just need views as input for another function f(), so I don't need to change the values. However it seems, that R is terribly slow for this task, or I'm doing something wrong (which seems more likely). The toy example illustrates how much time it takes just to select the columns, and then use them in another function (in this toy example the primitive function sum()). As 'benchmark' I also test the calculation time against summing up the whole matrix, which is surprisingly faster. I also experimented with the package