取消stringByEvaluatingJavaScriptFromString

Question

I have JS thats called using stringByEvaluatingJavaScriptFromString and takes around 9 seconds to run, but I'd like to be able to cancel this immediately if the user so requires.

It seems however that the entire thread is blocked by this.

I would be prepared to do anything to allow the user to cancel this (eg remove the UIWebView ) but nothing seems to work as the app waits for the stringByEvaluatingJavaScriptFromString to return before continuing.

Answer 1

Not sure how to cancel it. In order to improve the UI, from this UIWebView stringByEvaluatingJavaScriptFromString in background ,

Try splitting up your JavaScript into discrete execution blocks and pipeline them using a JavaScript timer, like this (JS code, not Obj-C):

var i = 0;
var operation = function() {

    switch (i) {
    case 0:
       //do first part of code
       break;
    case 1:
       //do second part of code
       break;
    case 2:
       //do third part of code
       break;
    etc...
    }

    //prepare to execute next block
    i++;
    if (i < TOTAL_PARTS) {
        setTimeout(operation, 0);
    }
};
operation();

That will prevent your script from blocking user interaction while it executes.

For more details please check that thread, UIWebView stringByEvaluatingJavaScriptFromString in background .