javascript - 动态创建Canvas并添加onmousedown功能

Question

我需要在运行时动态创建多个 Canvas 元素。我已经成功地创建了 Canvas ，但将“onmousedown”属性设置为方法已证明很困难。这可能是因为我需要通过函数传递 Canvas 元素，尽管我不确定。有人可以帮忙吗？

谢谢!

下面您可以按顺序看到:原始静态 Canvas 、动态创建 Canvas 的循环以及我需要设置为“onmousedown”的函数。

<canvas id="Canvas1" onmousedown="MouseDown(this, event)" onmousemove="MouseMove(event)" onmouseup="MouseUp(event)" width="0" height="600" style="overflow: hidden; position: absolute; top: 0px;">

for(var i = 1; i < total; i++)
{
    var div = document.getElementById("Control");
    var canv = document.createElement('canvas');
    canv.id = "Canvas" + i.toString();         
    canv.width= 0+'px';
    canv.height= 600+'px';
    canv.style.overflow = 'hidden';
    canv.style.position = 'absolute'; 
    canv.style.top = 0+'px';

    div.appendChild(canv);
}

function MouseDown(can, e)
{

    MovingCanvas = can;
    alert("got here");
    clicked = true;
    MouseX = e.clientX;
    MouseY = e.clientY;

    StartX = MovingCanvas.style.left;
    StartY = MovingCanvas.style.top;
}

Answer 1

只需在循环内添加回调处理程序:

for(var i = 1; i < total; i++) {

    --- 8X ---

    /// add a callback handler here by referencing the function
    canv.onmousedown = MouseDown;

    div.appendChild(canv);
}

请注意，这只会给出一个参数，即事件。但没有必要，因为回调会将调用回调的当前 Canvas 绑定(bind)为 this；所以你可以修改你的回调函数:

/// callback only gives one argument to the function, the event
function MouseDown(e) {

    /// this will be current canvas that called this function
    MovingCanvas = this;

    --- 8X ---
}

当然这也需要修改:

<canvas id="Canvas1" onmousedown="MouseDown(event)" ...
                                            ^^^^^