getContext不是一个函数 [英] getContext is not a function
问题描述
我正在使用canvas来制作一个基本的web应用程序,当窗口调整大小时动态地更改画布大小。我已经得到它静态工作没有任何缺陷,但是当我创建一个对象使它动态,它在chrome中引发错误
I'm working on making a basic web application using canvas that dynamically changes the canvas size when the window resizes. I've gotten it to work statically without any flaws but when I create an object to make it dynamically it throws an error
错误是:
未捕获TypeError:Object [object Object]没有方法'getContext'
Uncaught TypeError: Object [object Object] has no method 'getContext'
,在firefox中是:
and in firefox it is:
this.element.getContext不是函数
this.element.getContext is not a function
我在网上搜索,似乎是一个常见的问题,但没有一个修正提出任何区别。
I've searched the web and it seems like a common problem but none of the fixes mentioned make any difference.
代码有问题如下:
layer['background'] = new canvasLayer("body","background");
function canvasLayer(location,id){
$(location).append("<canvas id='"+id+"'>unsupported browser</canvas>");
this.element=$(id);
this.context = this.element.getContext("2d"); //this is the line that throws the error
this.width=$(window).width(); //change the canvas size
this.height=$(window).height();
$(id).width($(window).width()); //change the canvas tag size to maintain proper scale
$(id).height($(window).height());
}
提前感谢。
推荐答案
您的价值:
this.element = $(id);
是一个jQuery对象,而不是纯Canvas元素。
is a jQuery object, not a pure Canvas element.
要返回,可以调用 getContext()
,调用 this.element.get(0)
,或者更好的存储真正的元素而不是jQuery对象:
To turn it back so you can call getContext()
, call this.element.get(0)
, or better yet store the real element and not the jQuery object:
function canvasLayer(location, id) {
this.width = $(window).width();
this.height = $(window).height();
this.element = document.createElement('canvas');
$(this.element)
.attr('id', id)
.text('unsupported browser')
.width(this.width)
.height(this.height)
.appendTo(location);
this.context = this.element.getContext("2d");
}
查看http://jsfiddle.net/alnitak/zbaMh/ ,最好使用Chrome JavaScript控制台,以便在调试输出中看到生成的对象。
See running code at http://jsfiddle.net/alnitak/zbaMh/, ideally using the Chrome Javascript Console so you can see the resulting object in the debug output.
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