I am using a UIWebView which is updated often using
- (void)loadHTMLString:(NSString *)string baseURL:(NSURL *)baseURL
The html string loaded changes to highlight the next word the user has to type in. To scroll the text as the user types, I use:
[webView stringByEvaluatingJavaScriptFromString:
[NSString stringWithFormat: #"window.scrollBy(0, %d);", yScroll]];
,which is called within
-(void) webViewDidFinishLoad:(UIWebView *)webView
inside the web view delegate.
Although this works, the web view is scrolled to the top each and every time it is loaded, and later scrolled to the right position, which causes an undesirable flicker.
Interestingly enough this flicker appears on the device but not on the simulator.
I have tried setting the offset alternatively like:
webView.scrollView.contentOffset = CGPointMake(0, yScroll);
which scrolls the web view but has no effect on the flicker.
I have also overriden
- (void)webViewDidStartLoad:(UIWebView *)webView
and set the hidden property of the web view to YES, made the scroll, and revealed the web view within the
-(void) webViewDidFinishLoad:(UIWebView *)webView
method but to no real effect.
My last resort would be trimming lines from the html string as the user types, loading the updated string every time and avoiding the scroll altogether.
Before I follow that path, does anyone have an idea on how to get the scrolling to work without the "flicker"?
Many thanks
Related
There are a few question about this, which has a solution regarding the script embedded in html string. Not in my case.
I have a ios5/6 app.
I have tryed to put the loading code into initWithNibName bad idea, viewDidLoad is deprecated , so viewWillAppear left.
- (void) viewWillAppear:(BOOL)animated
{
NSString* detailHtml = [Storage getDetailHtml: -1];// get the last one
//NSLog(#"detailHtml: %#", detailHtml);
if(detailHtml == nil){
NSLog(#"Can't load the detail");
detailHtml = #"<html><body>Some text here</body></html>";
}
[webView loadHTMLString:detailHtml baseURL:nil];
[super viewWillAppear:animated];
}
The problem with this code is flashing. It appears the UIViewContoller, with a white webView than after 1-2 seconds it is displayed the html. The HTML has some texts, but has base64 encoded images too, sometimes it is around 3Mb even 5MB content. No javascript is here, just inline CSS ( no external file ), text and base 64 encoded images.
I could pre-load into detailHtml the text, but I think the displaying takes more time.
Is that possible to do not display the ViewController, until the webView hasn't finished loading the html ? - some callback?
Any suggestions?
That would take little bit time to load the HTML string default.But if everything works fine the why don't you put UIActivityIndicator so that would keep user engaged with the app.Even much better than keeping it blank
Here is one the delegate method of UIWebView :
- (void)webViewDidFinishLoad:(UIWebView *)webView
{
//And stop your indicator over here
[indicator stopAnimating];
}
I want to set the back / forward button for my web view, so I check for canGoBack, canGoForward status in all 4 of the web view delegate methods. The delegate is set properly, and the methods are called in most cases. However, in a few cases they aren't called:
When I call [webView goBack] (for a certain links)
When I click to a link, go back, then click that link again (again, for a certain links).
I suspect it has something to do with the jquery mobile library or the html/css used in that page. However, Safari back button works properly.
So how can I track the back / forward button status, apart from making a timer?
Maybe you're missing webViewDidFinishLoading reset?
- (void)webViewDidFinishLoad:(UIWebView *)webView
{
webBack.enabled = [webView canGoBack];
webForward.enabled = [webView canGoForward];
}
In one of my apps I reuse a webview. Each time the user enters a certain view on reload cached data to the webview using the method :-
- (void)loadData:(NSData *)data MIMEType:(NSString *)MIMEType textEncodingName:(NSString *)encodingName baseURL:(NSURL *)baseURL
and I wait for the callback call
- (void) webViewDidFinishLoad:(UIWebView *)webView.
In the mean time I hide the webview and show a 'loading' label.
Only when I receive webViewDidFinishLoad do I show the webview.
Many times what happens I see the previous data that was loaded to the webview for a brief second before the new data I loaded kicks in.
I already added a delay of 0.2 seconds before showing the webview but it didn't help.
Instead of solving this by adding more time to the delay does anyone know how to solve this issue or maybe clear old data from a webview without release and allocating it every time?
Thanks malaki1974, in my case I wasn't using a modal view.
When I sat with an Apple engineer on WWDC 2010 and asked him this question his answer was simply: "Don't reuse UIWebViews, that's not how they were ment to be used."
Since then I make sure to calls this set of lines before allocating a new UIWebView
[self.myWebView removeFromSuperview];
self.myWebView.delegate = nil;
[self.myWebView stopLoading];
[self.myWebView release];
That solved the issue.
Clear the contents of the webview before you try to load new content
[self loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:#"about:blank"]]];
First, the UIWebView renders it contents in a background thread. Even when you receive webViewDidFinishLoad: it might not be completely done. Specially if it is an ajax-intense page that comes from the network.
You say you are hiding the view. I wonder if that means that the webview delays its drawing completely. What you could try is to move the UIWebView offscreen or obscure it with another view. Maybe that will change it's drawing behaviour.
If you do not need an interactive UIWebView then you can also consider to do it completely offscreen in a separate UIWindow and then create an image from that UIWebView's layer.
That's what I do, and it works:
[_webView stringByEvaluatingJavaScriptFromString:#"document.open();document.close();"];
Try loading a local file that is blank or has a loading graphic when you hide it, rather than just loading new content when you show it. Since the file is local it will be quick and even if the new page takes a while to load it will have either blank or loading expected behavior.
If you got controll over the html. You can communicate back to objective-c when the document is ready. Like so in jQuery:
function messageNative (name, string) {
var iframe = document.createElement("IFRAME");
iframe.setAttribute("src", "appscheme://" + name + "/" + string);
document.documentElement.appendChild(iframe);
iframe.parentNode.removeChild(iframe);
iframe = null;
}
$(function() {
messageNative('webview', 'ready');
});
And then in UIWebView's delegate method webView:shouldStartLoadWithRequest:navigationType: wait for the request with url equal to "appscheme://webview/ready". Then you should know: the document is loaded and ready for display. Then all that is missing is a simple fade-in or something like that :)
I have some code that needs to run after the a UIWebView finishes loading a document. For that I've set the UIWebView's delegate to my controller, and implemented the webViewDidFinishLoading method.
This gets called multiple times, depending on the type of page to load. I'm not sure if it's because of ajax requests, requests for images, or maybe even iframes.
Is there a way to tell that the main request has finished, meaning the HTML is completely loaded?
Or perhaps delay my code from firing until all of those events are done firing?
You can do something like this to check when loading is finished. Because you can have a lot of content on the same page you need it.
- (void)webViewDidFinishLoad:(UIWebView *)webview {
if (webview.isLoading)
return;
// do some work
}
It could be enlightening (if you haven't gone this far yet) to NSLog a trace of load starts and finishes.
- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType {
NSLog(#"Loading: %#", [request URL]);
return YES;
}
- (void)webViewDidFinishLoad:(UIWebView *)webView {
NSLog(#"didFinish: %#; stillLoading: %#", [[webView request]URL],
(webView.loading?#"YES":#"NO"));
}
- (void)webView:(UIWebView *)webView didFailLoadWithError:(NSError *)error {
NSLog(#"didFail: %#; stillLoading: %#", [[webView request]URL],
(webView.loading?#"YES":#"NO"));
}
I just watched the calls to all three in one of my projects which loads a help page from my bundle and contains embedded resources (external css, YUI!, images). The only request that comes through is the initial page load, shouldStartLoadWithRequest isn't called for any of the dependencies. So it is curious why your didFinishLoad is called multiple times.
Perhaps what you're seeing is due to redirects, or as mentioned, ajax calls within a loaded page. But you at least should be able balance calls to shouldStartLoad and either of the other two delegate functions and be able to determine when the loading is finished.
Check this one it so simply and easy way to achieve no need to write too much code:
- (void)webViewDidFinishLoad:(UIWebView *)webView {
if ([[webView stringByEvaluatingJavaScriptFromString:#"document.readyState"] isEqualToString:#"complete"]) {
// UIWebView object has fully loaded.
}
}
This question is already solved, but I see it lacks an answer that actually explains why multiple calls to webViewDidFinishLoad are actually expected behavior
The aforementioned method is called every time the webview finishes loading a frame. From the UIWebViewDelegate protocol documentation:
webViewDidFinishLoad:
Sent after a web view finishes loading a frame.
In fact, this is also true for all the other methods that comprise the UIWebViewDelegate protocol.
Try this it will work fine
-(void)webViewDidFinishLoad:(UIWebView *)webview
{
if (webview.isLoading)
return;
else
{
// Use the code here which ever you need to run after webview loaded
}
}
This happens because the callback method is called every time a frame is done loading. In order to prevent this set the "suppressesIncrementalRendering" property of the webview to true. this will prevent the webview from rendering until the entire data is loaded into the memory. This did the trick for me
I have notice something similar and it was a confusion: I have a UITabBarController, it seems to preload all ViewControllers linked to its tabs on launching the App (in spite of showing just first_Tab_ViewController), so when several tabs have ViewController with WebView their respective webViewDidFinishLoad are called and if I have copied pasted:
NSLog(#"size width %0.0f height %0.0f", fitingSize.width, fittingSize.height);
in several, I get several output in console that appears to be a double calling when they really are single calling in two different UIWebViews.
You could check the loading and request properties in the webViewDidFinishLoad method
Possibly related to this issue is a property on UIWebView introduced in iOS6: suppressesIncrementalRendering.
I'm trying to transition between loading of different web pages by hiding the webView while it is loading a page. However, I'm seeing that some image intensive websites are causing webViewDidFinishLoading to fire too soon and when I show the webView at that point then for a split second you get a view of the previous page. Any ideas on how to resolve this?
If there's Javascript on the page, you may need to wait for it to finish. The easiest way seems to be to send some javascript to the page to be executed:
-(void) webViewDidFinishLoad:(UIWebView *)webView
{
NSString *javaScript = #"<script type=\"text/javascript\">function myFunction(){return 1+1;}</script>";
[webView stringByEvaluatingJavaScriptFromString:javaScript];
// done here
}
Having said that, I seem to still see cases where the webview isn't quite updated within webViewDidFinishLoad.
I've encountered this problem as well. Although I haven't found a solution, I've worked around the problem by introducing a 0.5 second delay before showing the UIWebView once the webViewDidFinishLoading delegate method is called.
- (void)webViewDidFinishLoad:(UIWebView *)webView
{
[self performSelector:#selector(displayWebView) withObject:nil afterDelay:0.5];
}