Sketch.js pageX undefined error

问题

I am using sketch.js by intridea in my phonegap application.It works allright with the modification

 case 'touchstart':
            if (this.painting) {//add
                this.stopPainting();
                //add
            }//add
            this.startPainting();
            break;

by adding the above lines to the code.But I am getting a pageX undefined error which is crashing my app.

01-23 19:53:59.342: E/Web Console(31932): Uncaught TypeError: Cannot read property 'pageX' of undefined at file:///android_asset/www/js/external_libs/sketch.js:107

How to overcome this issue,any help would be appreciated.Thanks

回答1:

It seems as if everyone has swtiched over to jqscribbel.js, but to directly answer this question with sketch.js, you need to check if e.originalEvent.targetTouches[0] is defined. I haven't dug into sketch.js too much yet, but it seems that when a touchup event is triggered, e.originalEvent.targetTouches[0] is no longer defined, so trying to find .pageX of undefined gives an error. This error causes the entire canvas to be re-drawn, so you cannot draw more than 1 sketch on the canvas. To fix this error, simply add find the following two lines of code (around line 100/101):

e.pageX = e.originalEvent.targetTouches[0].pageX;
e.pageY = e.originalEvent.targetTouches[0].pageY;

and replace with

if (e.originalEvent.targetTouches[0] !== undefined && e.originalEvent.targetTouches[0].pageX !== undefined){
    e.pageX = e.originalEvent.targetTouches[0].pageX;
}
if (e.originalEvent.targetTouches[0] !== undefined && e.originalEvent.targetTouches[0].pageY !==undefined){
    e.pageY = e.originalEvent.targetTouches[0].pageY;
}

来源：https://stackoverflow.com/questions/21311073/sketch-js-pagex-undefined-error