React:每次渲染都会调用 onClick 处理程序? [英] React: onClick handler is getting called on every render?

问题描述

我正在学习 React，并按照 本教程 创建了一个简单的您可以在 CodePen 中在此处查看的井字游戏.p>

我对箭头函数在 Square 组件的 onClick 属性中的工作方式感到困惑，该属性在 Board 组件的 renderSquare 函数内部返回:onClick={() =>this.props.onClick(i)}.同样同样是我有 onClick={ (i) => 的 Game 组件.this.handleClick(i)}.我以为我可以在没有箭头函数的情况下编写它(就像 onClick={this.handleClick(i)} 一样)但这会破坏游戏.

解决方案

onClick 需要一个函数.箭头函数没有自己的this；使用封闭执行上下文的 this 值.箭头函数是以下的替代品

onClick={this.handleClick.bind(this,i)}

当你运行它时它不起作用

onClick={this.handleClick(i)}

因为在这种情况下，它将调用一个函数，并且该函数将传递一个返回值，该返回值将在每次调用 render 时进行评估.因此，如果您在 onClick 函数中执行导致重新渲染的操作，例如 setState，您的应用程序将陷入无限循环.因此 onClick 需要一个函数而不是一个值，所以除非你从 onClick 处理程序返回一个函数，否则你不应该直接调用它.

上面的箭头函数起到了将参数绑定到函数的作用

I am learning React, and followed this tutorial to create a simple Tic-Tac-Toe game that you can view here in CodePen.

I am confused about how the arrow function works in the onClick property of the Square component that is being returned inside of the renderSquare function of the Board component: onClick={() => this.props.onClick(i)}. And also again similarly the Game component where I have onClick={ (i) => this.handleClick(i)}. I assumed I could write it without the arrow function (just like onClick={this.handleClick(i)}) but this breaks the game.

解决方案

onClick expects a function. An arrow function does not have its own this; the this value of the enclosing execution context is used. Arrow function is a replacement for the following

onClick={this.handleClick.bind(this,i)}

It doesn't work when you run it like

onClick={this.handleClick(i)} 

because in this case it will call a function and that will pass a return value that will be evaluate everytime render is called. So if you are doing somethings in the onClick function that causes a rerender for instance setState you app will go in an endless loop. Thus onClick needs a function and not a value so unless you are returning a function from the onClick handler you should not directly call it.

Arrow function above performs the role of binding the parameter to the function

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