Clear UIWebView cache when use local image file - ios

Question

I use a UIWebView to load a local html, and there is a PNG file inside the html created by Objc.
After the PNG file has been modified, I reload the html in UIWebView, but the image doesn't change. However, if I quit the app and reopen it, the image file will be changed to the new one.
I have checked the PNG file in Documents with Finder, so I'm sure it has been modified, but the old one is still in UIWebView.
So, as I think that it's a UIWebView cache problem, I've tried:
[[NSURLCache sharedURLCache] removeAllCachedResponses];
[_webView loadRequest:[NSURLRequest requestWithURL:[NSURL fileURLWithPath:url isDirectory:NO ] cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData timeoutInterval:1]]; or NSURLRequestReloadIgnoringCacheData
None of them works, and I can't change the filename, because the PNG file is used in a lot of places (other html and objc code).
I've tried this too:
some.png?r=randomNumber
but it can't be showed.
How do I clear the UIWebView cache when using a local image file inside a local html?

Answer 1

Other than renaming every file on each access, I've only seen one thing work for this and that is modifying the HTML with javascript to add a timestamp onto the image url so it tricks the webview into thinking it's a different file. Images (usually) load the same no matter what you put after the ? in their url. I think this would be easier than renaming every file each time you load the web view. Something like this (using jQuery):
<img src="myimg.jpg" />
<script>
$(function() {
$('img').each(function(i, el) {
$(el).attr('src', $(el).attr('src')+'?pizza='+(new Date()).getTime());
});
});
</script>
I guess this is assuming that this javascript loads and runs before the images are loaded, but in theory this should work.
For a little background, I've made a page in a webview that used RequireJS to asynchronously load quite a few files. I had the EXACT same problem that this question is talking about except that I was loading javascript files instead of images. The key to fixing this issue was adding a timestamp to every path of javascript file and thus tricking the webview (ex me.js?ts=236136236 and whatever.js?ts=3153524623). I found this to work great.
One other thing I needed to do was add a timestamp to the path of my HTML file when loading it into the webview like this:
[NSURL URLWithString:[[NSString stringWithFormat:#"%#/index.html?pizza=%f", webDirectoryPath, [[NSDate date] timeIntervalSince1970]]
I now can modify all the local files and each time the webview appears the changes come through.

Answer 2

You can try this, in your AppDelegate.m
+(void)initialize {
[[NSURLCache sharedURLCache] setDiskCapacity:0];
[[NSURLCache sharedURLCache] setMemoryCapacity:0];
}

Answer 3

If your html didn't change and the only change was in image you should use UIWebView's reload message instead of loading request again.
Something like this:
- (void)reloadWebView:(id)sender
{
if (self.loaded) {
[self.webView reload];
} else {
NSString *html = [[NSBundle mainBundle] pathForResource:#"web" ofType:#"html"];
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL fileURLWithPath:html]];
[self.webView loadRequest:request];
self.loaded = YES;
}
}
You don't even need any manipulations with cache.