webview can't run my file

I have a trouble all the time.

The question is I use other javascript and html file draw some picture in the webview.

But I change other view and turn back this view , it will crash.

I guess is the draw map listener not remove.

my original is below:

gChart function is in a javascript file, it will deal with some data and return a website.

drawBaseMap function is in the Html5/chart.html .

app.js

var myWebView = Ti.UI.createWebView(
        {
            url: 'Html5/chart.html'      // -> set url 
            top: 0,
            left: 0,
            width:  320 ,
            height: 160 ,
            scalesPageToFit: true
 
        }
    );
 
myWebView.addEventListener('load',function(e){ myWebView.evalJS("Ti.App.addEventListener('drawBaseMapHandler',function(e){" +"var gObj=gChart(e.strUrl);"+"drawBaseMap(gObj);"+"})"); });

api.js

// this fire event is in callback function
 
Ti.App.fireEvent('drawBaseMapHandler',{strUrl:arrData[2]});

This method can right run, but when I change view , it will crash.

I guess the "drawBaseMapHandler" listener is not remove.

So I change my code is below.

app.js

var runjs = function(e){ "var gObj=gChart("+Gval.strUrl+");"+"drawBaseMap(gObj);"};
 
myWebView.addEventListener('load',function(e){ myWebView.evalJS("Ti.App.addEventListener('drawBaseMapHandler', runjs);   Ti.App.removeEventListener('drawBaseMapHandler',runjs) "); });

Using this metohd can't show on the webview.

Because my Gval.strUrl ( it is global variable) hasn't write data.

I test my code to assign Gval.strUrl value , avoid the time problem.

But the webview still have not show my map.

So I try again to chang my code. below:

I take webview listener to my callback function and remove drawBaseMapHandler listener sentence.

app.js

var myWebView = Ti.UI.createWebView(
        {
            url: 'Html5/chart.html'      // -> set url 
            top: 0,
            left: 0,
            width:  320 ,
            height: 160 ,
            scalesPageToFit: true
 
        }
    );
 
 
var callbackFun = function(e)
{ 
      // e.url have right site
 
      pressWebView.addEventListener('load',function(e){ pressWebView.evalJS("var gObj=gChart(" + e.url+");" +"drawBaseMap(gObj);"); });
}
 
require('api').getMyData(Gval, callbackFun );

Using this method is not draw my map in mywebview.

why I use other javascript file and html to draw map in chart.html should through custom listener event draw my map only ?

Have any one can give me some suggestion?

I'm appricated your priceless opinions.