UIWebView stringByEvaluatingJavaScriptFromString debugging

Question

I'm trying to achieve a relatively simple result - focus on a textBox when page is loaded. I use this code:

[_webView setKeyboardDisplayRequiresUserAction:NO];

NSString *javaString = [NSString stringWithFormat:@"document.getElementById('keyboard').focus()"];
NSString *result = [_webView stringByEvaluatingJavaScriptFromString:javaString];

It's called by a button click in my app. This code worked on the test page, but doesn't work on the actual site. The worst part is that I don't know any way to debug this.

Nothing happens and result is always empty string. How do I check if there's an error in JS code? Or it can't find the object? Or it can't focus on it?

UPDATE

As rightly noted by @subzero, I forgot the actual focus() method in the question. It's correct now.

Community · Accepted Answer · 2017-05-23 12:07:23Z

2

You forgot to add the focus action

document.getElementById('keyboard').focus();"

will do the trick

About checking JS errors. There are 2 ways to do it.

The easy one: Add this (I'm ussing jQuery). It will show the errors at the bottom of the page

$( document ).ready(function() {

window.onerror = function(err) {
    log('window.onerror: ' + err)
}
var uniqueId = 1
function log (message, data) {
        var log = document.getElementById('log')
        var el = document.createElement('div')
        el.className = 'logLine'
        el.innerHTML = uniqueId++ + '. ' + message + ':<br/>' + JSON.stringify(data)
        if (log.children.length) { log.insertBefore(el, log.children[0]) }
        else { log.appendChild(el) }
}

in your html:

<div id='log'></div>

See this What are some methods to debug Javascript inside of a UIWebView?

edited May 23, 2017 at 12:07

CommunityBot

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answered May 5, 2015 at 15:40

subzero

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1 Comment

NKorotkov Over a year ago

Thanks a lot for the debugging tips. And of course I forgot the focus() action in the question, it's there in the actual code.

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