事件处理程序无响应 [英] Event handlers not responding

问题描述

我从JavaScript和D3开始，尝试编写一个简单的代码，使用户可以在画布上绘制曲线.第一步是能够检测到鼠标按钮何时按下，以便在按钮按下时移动鼠标，就可以记录数据.

I'm beginning with JavaScript and D3 and trying to write a simple code that allows users to draw a curve on a canvas. The first step is being able to detect when a mouse button is down, so that if the mouse moved while the button was down, data would be recorded.

我尝试将".on"更改为".addEventListener"，结果相同.另外，我正在使用Firefox.

I tried changing ".on" to ".addEventListener" with the same results. Also, I'm using Firefox.

当阅读下面的代码时，我知道每次移动鼠标时都将clickState标志增加是没有意义的.我这样做只是为了调试，以查看是否在鼠标移动时调用了mousemovefx函数.

When reading the code below, I know it makes little sense to have the flag clickState incremented every time the mouse is moved; I only did that for debugging purposes to see if the function mousemovefx was being called upon mouse motion.

当我打开此网页时，输出div中的文本立即变为向下"，而我所做的任何操作(例如单击并在画布中移动)都不会对其进行更改.其他功能似乎也没有执行.

When I open this webpage, the text in the output div changes immediately to "Down" and nothing I do (e.g. clicking and moving in the canvas) changes it. None of the other functions seem to be executed either.

我既不理解(a)为什么未在这些事件上调用处理程序，又不理解(b)为什么不立即单击而鼠标甚至不在画布上时立即调用mousedown处理程序

I neither understand (a) why the handlers aren't being called on those events nor (b) why the mousedown handler is being called immediately, when not only am I not clicking but my mouse isn't even on the canvas.

    document.body.style.backgroundColor = "black";

    canvw = 500;
    canvh = 500;
    border = 6;

    clickState = 0;

    var canvas = d3.select("body")
                    .append("svg")      //Add an SVG to the body
                    .attr("width",canvw+2*border)
                    .attr("height",canvh+2*border)

    var canvbg = canvas.append("rect")
                    .attr("x",border)
                    .attr("y",border)
                    .attr("width",canvw)
                    .attr("height",canvh)
                    .attr("fill","white")
                    .attr("stroke","rgb(200,200,200)")
                    .attr("stroke-width",5)

    var mydiv = d3.select("body")
                    .append("div")
                    .attr("id","outputdiv")
                    .style("color","orange")

    canvas.on("mousedown", mousedownfx());

    canvas.on("mouseup", mouseupfx());

    canvas.on("mousemove",mousemovefx());

    canvas.on("mouseout",mouseoutfx());

    function mousedownfx() {
        clickState = 1;
        mydiv.text("Down")
    }

    function mouseupfx() {
        clickState = 0;
        mydiv.text("Up")
    }

    function mousemovefx() {
        mydiv.text(clickState)
        clickState = clickState + 1;
    }

    function mouseoutfx() {
        clickstate = 0;
    }

推荐答案

document.body.style.backgroundColor = "black";

    canvw = 500;
    canvh = 500;
    border = 6;

    clickState = 0;

    var canvas = d3.select("body")
                    .append("svg")      //Add an SVG to the body
                    .attr("width",canvw+2*border)
                    .attr("height",canvh+2*border)

    var canvbg = canvas.append("rect")
                    .attr("x",border)
                    .attr("y",border)
                    .attr("width",canvw)
                    .attr("height",canvh)
                    .attr("fill","white")
                    .attr("stroke","rgb(200,200,200)")
                    .attr("stroke-width",5)

    var mydiv = d3.select("body")
                    .append("div")
                    .attr("id","outputdiv")
                    .style("color","orange")

    canvas.on("mousedown", mousedownfx);

    canvas.on("mouseup", mouseupfx);

    canvas.on("mousemove",mousemovefx);

    canvas.on("mouseout",mouseoutfx);

    function mousedownfx() {
        clickState = 1;
        mydiv.text("Down")
    }

    function mouseupfx() {
        clickState = 0;
        mydiv.text("Up")
    }

    function mousemovefx() {
        mydiv.text(clickState)
        clickState = clickState + 1;
    }

    function mouseoutfx() {
        clickstate = 0;
    }

<script src="https://d3js.org/d3.v5.min.js"></script>

设置侦听器时，您将调用函数更改:

When you are setting the listeners you are calling the function change:

canvas.on("mousedown", mousedownfx());
canvas.on("mouseup", mouseupfx());
canvas.on("mousemove",mousemovefx());
canvas.on("mouseout",mouseoutfx());

收件人:

canvas.on("mousedown", mousedownfx);
canvas.on("mouseup", mouseupfx);
canvas.on("mousemove",mousemovefx);
canvas.on("mouseout",mouseoutfx);

这将传递该函数，然后在单击按钮时调用该函数.

This will pass the function, which will then be called when the button is clicked.

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