首先添加一个按钮，点击它的时候执行清缓存和cookie操作，这里我重写了导航的返回按钮：
-(void)leftBarButtonClicked{
_webView = nil;
[self cleanCacheAndCookie];
[self.navigationController popViewControllerAnimated:YES];
}
/**清除缓存和cookie*/
- (void)cleanCacheAndCookie{
//清除cookies
NSHTTPCookie *cookie;
NSHTTPCookieStorage *storage = [NSHTTPCookieStorage sharedHTTPCookieStorage];
for (cookie in [storage cookies]){
[storage deleteCookie:cookie];
}
//清除UIWebView的缓存
[[NSURLCache sharedURLCache] removeAllCachedResponses];
NSURLCache * cache = [NSURLCache sharedURLCache];
[cache removeAllCachedResponses];
[cache setDiskCapacity:0];
[cache setMemoryCapacity:0];
}
