How to determine why WKWebView is crashing - ios

I am using WKWebView in a Swift app built for iOS 8+. I use instances of WKWebView in a variety of views in my app, e.g. in each of the tabs in my tab view controller, the interface is based on WKWebView.
I and my testers have noticed these views sometimes go completely blank, and after researching that issue, it seems that WKWebView can crash, and the blank view is the result. Luckily, it doesn't bring down the app due to the way WKWebView operates, but I also am not clear on how to trap/log information about what caused it to crash (if that is actually what is happening).
How can I determine if/why a WKWebView has crashed?
My current workaround for the issue is that I use KVO (actually, Facebook's KVOController), to monitor the "URL" property of the WKWebView, and if it goes from non-nil to nil, I assume a crash has happened, and I reload the webview:
kvoController?.observe(webView, keyPath: "URL", options: NSKeyValueObservingOptions.New|NSKeyValueObservingOptions.Old) { (areaViewController, webView, change) -> Void in
if change[NSKeyValueChangeNewKey] is NSNull && !(change[NSKeyValueChangeOldKey] is NSNull) {
areaViewController.setup() // reload our webview
}
}
But obviously it would be nice to figure out the root cause of the crash.

This is very nasty WKWebView issue that we also encountered in Firefox for iOS.
See the following bug report https://bugs.webkit.org/show_bug.cgi?id=148685
I have no great solution but I do have two tips:
First, we were also doing the reload when we found out via KVO that webView.URL turned nil. However it turns out that it turns nil on a number of events. For example when a redirect happens and possibly also when a form is submitted. So this is not ideal.
Second, in iOS9 there is a new API to detect when the WebKit content process has died. We have not tried this yet but I think that will be a better trigger to reload the webView.
There is no documentation yet I think, but you can see this in the header files:
- (void)webViewWebContentProcessDidTerminate:(WKWebView *)webView NS_AVAILABLE(10_11, 9_0);

(void)webViewWebContentProcessDidTerminate:(WKWebView *)webView NS_AVAILABLE(10_11, 9_0); This delegate getting called only in iOS9.but if you reload webview ,you will lost all of the state information stored.
maybe can save info befor called [webview reload]
for example:
NSString *jsString = #"var arry=[];
for(var i=0; i<sessionStorage.length; i++){
var a={};a[sessionStorage.key(i)]=sessionStorage.getItem(sessionStorage.key(i));arry.push(a)};arry";
[webView evaluateJavaScript:jsString completionHandler:^(id _Nullable obj, NSError * _Nullable error) {
NSLog(#"jsString1===error=%#",error);
NSLog(#"jsString1==obj==®%#",obj);
if (obj == NULL ||obj ==[NSNull class]||obj==nil) {
//重启webview
[webView reload];
return ;
}
//保存sessionStorage
NSArray *arr = (NSArray*)obj;
//保存后重启webview
[webView reload];
}];

Related

UIWebView white screen on every launch while preloading all tabs

Before I present my issue, I want to mention that I tried looking for solutions here and here.
I am creating a hybrid application which uses native UIWebView for rendering the responsive designed web application. Following is the issue description :
1. I have a UITabBarController.
2. Each of the tab has a UIWebView.
3. I have to preload all tabs.
4. I am showing a UIActivityIndicator till the content loads on the first tab.
5. White screen appears for about 8-10 seconds and then the content starts to appear.
I will be happy to see this time become 2-4 seconds.
Following is my implementation :
[self performSelectorOnMainThread:#selector(loadAllTabs) withObject:nil waitUntilDone:YES];
-(void) loadAllTabs
{
for(UIViewController * viewController in self.viewControllers){
if(![[NSUserDefaults standardUserDefaults]boolForKey:#"isSessionExpired"])
{
if((int)[self.viewControllers indexOfObject:viewController] != 4)
{
viewController.tabBarItem.tag = (int)[[self viewControllers] indexOfObject:viewController];
[viewController view];
}
}
}
}
In WebView controller's viewDidLoad I have :
[_tgWebView loadRequest:[NSURLRequest requestWithURL:homeURL]];
I was looking forward to suppressesIncrementalRendering, but since I am preloading all tabs, this does not work.
Since my app supports iOS 7+, thus WKWebView can't be applied here.
I also thought of increasing the launch image duration but learned that is won't be a good practice.
Can this be implemented using GCD?
Please bring out the pitfalls in my implementations so that my application makes better performance.
First, have UIWebView on each tab hidden until it has finished loading, then show it. Underneath the UIWebView you can have some placeholder image to describe it loading. Then using the webViewDidFinishLoad delegate method show the web view when it has finished loading. This approach will be non blocking.
- (void)webViewDidFinishLoad:(UIWebView *)webview
{
if (webview.isLoading)
return;
else
webView.hidden = false;
}
Second, preload the first tab then load the subsequent tabs while displaying the first. You can do that by placing the following code in the first tabs viewDidLoad method:
// Preload the subsquent tabs
for (UIViewController *aVC in self.tabBarController.viewControllers)
if ([aVC respondsToSelector:#selector(view)] && aVC != self)
aVC.view;
This way, the additional tabs web views are loaded in the background in a non blocking manner. You could combine it with hiding the web views while loading in case the user navigates to the additional tabs before their pages load.
I tested this with three tabs and it worked nicely.
So the first view controller could look something like this:
#implementation FirstViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Load the website
[self loadWebView];
// Preload the subsquent tabs
for (UIViewController *aVC in self.tabBarController.viewControllers)
if ([aVC respondsToSelector:#selector(view)] && aVC != self)
aVC.view;
}
-(void)loadWebView
{
// Create Request
NSURL *url = [NSURL URLWithString:#"http://anandTech.com"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
// Load the page
[webView loadRequest:request];
}
- (void)webViewDidFinishLoad:(UIWebView *)webview
{
if (webview.isLoading)
return;
else
webView.hidden = false;
}
EDIT:
Removed GDC as it was crashing when the views had WebViews
This post made my day. I am now using NSNotificationCenter for this.
It's hard to identify the where the problem is directly.
First, I suggest that you check your network connection by loading the page on a desktop machine on the same Wifi to see if it is your server that is too slow.
Also you can load your pages one by one instead of load all pages concurrently, since multiple HTTP request are not processed in a FIFO sequence, they may be processed out of order, and your page may need all resource to be loaded before displaying.
Do you control the web page your self? You can use safari inspector to inspect your web page to see where is the time spent, is it resource loading, javascript processing or rendering.

UIWebView screenshot

I'm facing a problem trying to take screenshots form UIWebViews. I need to take some screenshots of my UIWebView and it works but the screenshot is not correct because they are taken in the event webViewDidFinishLoad, but it calls webViewDidFinishLoad when the UIWebView is not loaded fully, I mean, I take the screenshot in the event webViewDidFinishLoad but the UIWebView is not correctly and fully loaded so it takes a screenshot and it makes right but the screenshot is not totally correct because its the event is triggered (webViewDidFinishLoad) but the UIWebView is not totally loaded. Any ideas?
Thank you very much
A user was having a issue with their use of a activity indicator that apears until a page has loaded but theirs would come back after the main content had loaded the question is here UIWebView not finishing loading? and the answer code is used below. After the code I will go into detail about how this could be used for your situation.
(In the code below the web page truly starts loading on //show UIActivityIndicator and truly finishes loading the main content (not the extra content you are struggling with) on //hide UIActivityIndicator)
//Define the NSStrings "lastURL" & "currentURL" in the .h file.
//Define the int "falsepositive" in the .h file. (You could use booleans if you want)
//Define your UIWebView's delegate (either in the xib file or in your code)
- (void)webViewDidFinishLoad:(UIWebView *)webView {
lastURL = [[NSString alloc] initWithFormat:#"%#", webView.request.mainDocumentURL];
if (falsepositive != 1) {
NSLog(#"Loaded");
//hide UIActivityIndicator
} else {
NSLog(#"Extra content junk (i.e. advertisements) that the page loaded with javascript has finished loading");
//This method may be a good way to prevent ads from loading hehe, but we won't do that
}
}
-(BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType; {
NSURL *requestURL =[request mainDocumentURL];
currentURL = [[NSString alloc] initWithFormat:#"%#", requestURL]; //not sure if "%#" should be used for an NSURL but it worked...
return YES;
}
- (void)webViewDidStartLoad:(UIWebView *)webView {
if ([currentURL isEqualToString:lastURL]) {
falsepositive = 1;
NSLog(#"The page is loading extra content with javascript or something, ignore this");
} else {
falsepositive = 0;
NSLog(#"Loading");
//show UIActiviyIndicator
}
}
When a page loads in iOS, webviewdidstart and webviewdidfinish are called but not knowing the difference in your main page/html content objective-c calls this again for extra content such as ads or frames. Using this if I were in your situation I would create a BOOL such as pageIsLoading and set it to true in webviewdidstart and then set it to false in webviewdidfinish. After the BOOL is turned off in webviewdidfinish I would end webviewdidfinish by calling a method that will check after a short delay if the BOOL pageIsLoading == YES and if it is, do nothing because more content is loading. If pageIsloading == no then all content must be loaded and now would be a good time to take your snapshot.
Rather than taking screenshot in the event webViewDidFinishLoad you can try to take the screenshot explicitly using UIButton. Let this button be disabled and you can just set this button's enabled property to YES after web view fully loads its content.
On button click to can implement your code to take screenshot.
Edited : Webview's webViewDidFinishLoad method is called when it finishes loading its content. Might be its possible that it may be taking some time to render some images/content on its view.
If possible you can use NSTimer in your webViewDidFinishLoad method to wait for sufficient time(1 min) so that mean while webview can load its content fully.
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:60.0
target: self
selector: #selector(MethodName:)
userInfo: nil
repeats: NO];
In Selector method you can implement your code of taking screenshot.
Hope this will help you...

Can a UIWebView interact (communicate) with the app?

I went to use UIWebView to display dynamic content, instead of doing it natively using UI-elements. Is it possible to trigger native app functions from simply hitting links inside the UIWebView? Example: hitting a link which then switches current View?
Yes, it's possible. In your html, you write a JS to load a URL with a fake scheme such as
window.location = "request_for_action://anything/that/is/a/valid/url/can/go/here";
Then, in your iOS code, assign a delegate to your webView, and in your delegate, handle
webView:shouldLoadWithRequest:navigationType
with something like
if( [request.URL.scheme isEqualToString: #"request_for_action"] )
{
// parse your custom URL to extract parameter, use URL parts or query string as you like
return NO; // return NO, so webView won't actually try to load this fake request
}
--
Just an aside, you can do the other way, let iOS code invoke some JS codes in your html by
using
NSString* returnValue = [self.webView stringByEvaluatingJavaScriptFromString: "someJSFunction()"];
Yes! When the user presses a link, you hear about it in the web view's delegate and can then do whatever you want. Powerful stuff can be done this way.
The web view's delegate is sent webView:shouldStartLoadWithRequest:navigationType:. You analyze what happened, and respond as you wish. To prevent the web view from trying to follow the link (which may be completely fake, after all), just return NO.
In this example from the TidBITS News app, I have a link in the Web page that uses a totally made-up play: scheme. I detect that in the delegate and play:
- (BOOL)webView:(UIWebView *)webView
shouldStartLoadWithRequest:(NSURLRequest *)r
navigationType:(UIWebViewNavigationType)nt {
if ([r.URL.scheme isEqualToString: #"play"]) {
[self doPlay:nil];
return NO;
}
if (nt == UIWebViewNavigationTypeLinkClicked) {
[[UIApplication sharedApplication] openURL:r.URL];
return NO;
}
return YES;
}
Implement the UIWebViewDelegate method webView:shouldStartLoadWithRequest:navigationType:.
Handle navigationType and the request as needed.

Objective-C calling javascript in UIWebView calling back Objective-C; threading issues

I have a UIWebView-based application that is storing some state. I have a native tab bar and upper bar however. What I need is that when I click on the native bar, I persist the data stored in the UIWebView.
To do this, I called evaluateJavaScriptByString to create a JSON object and it does a callback to objective-C via the UIWebViewDelegate protocol.
However, I find that the callback is asynchronous and hence my main transaction happens before the data is loaded.
Any idea how this problem can be solved?
Update: To explain the problem better:-
I have an HTML page with a form that someone puts some data into.
My Tab bar is native.
On the click of a button on the tab bar, I want the data from HTML saved to an Objective-C model, and the view should change to some other view.
What is happening is that once I click the button, the javascript call happens to the page (to create a JSON string to send to Objective-C) and this data does get saved to the obj-c model. However, this happens asynchronously. So my screen changes before the data is loaded into the model. If I refresh the next screen it shows the correct data. I was wondering if there was a way around this.
Note, I know how to call OBjective-C functions from WebViews. We are using JSOBjBridge for that anyway.
Just add something like this #"some_var = MAKE_JSON(); window.location = \"myapp://callback/\" + escape(some_var)" at the end of your javascript code, that you transfer to evaluateJavaScriptByString:
In UIWebView's delegate implement webView:shouldStartLoadWithRequest:navigationType: and catch all urls with myapp:// prefix like this:
- (BOOL) webView: (UIWebView *) webView
shouldStartLoadWithRequest: (NSURLRequest *) request
navigationType: (UIWebViewNavigationType) navigationType {
NSString *url = #"myapp://";
NSString *path = request.mainDocumentURL.relativePath;
NSString *callbackURL = #"callback/";
if ( [path hasPrefix:url] ) {
path = [path substringFromIndex:[url length]];
if ( [relPath hasPrefix:callbackURL] ) {
NSString *json = [path substringFromIndex:[callbackURL length]];
//TODO: Work with json
}
return NO;
}
return [super webView:webView shouldStartLoadWithRequest:request navigationType: navigationType];
}
I didn't test this code, I just written it from scratch, but it should work, I already did it in this way.

iCloud - renaming open documents on another device sometimes fails

The issue: I'm working on an iCloud document on device A, e.g. iPod Touch. Then I change the name of the document on device B, e.g. my Mac (via the Finder). The change goes up to the cloud and after a pause device A gets to hear about it.
And then:
some of the time all is just fine - I pick up the change of name via a changed fileURL property and can update my interface accordingly - the document continues to behave just as it should
some of the time, the document's fileURL is returned as something such as: file://localhost/var/mobile/Library/Mobile%20Documents/.ubd/peer-43A0AEB6-84CE-283E-CA39-FCC4EF3BC8F8-v23/ftr/purg-012fdcfbe3b3bbce6e603fdfd2f000b2cb28649e95 Not surprisingly this file won't save.
Can anyone explain what is going on and how to work around it?
Background
The name change is picked up fine by by NSMetadataQuery. So, for e.g., I can rename documents that are not open and all my iCloud functionality works fine. The issue only seems to occur with open documents.
Other iCloud features are working fine, e.g. I can change content on one device, e.g. my Mac, and detect and then update my interface on another device, e.g. my iPod Touch, that has the relevant iCloud document open.
I first spotted this when I added an override for presentedItemDidMoveToURL: to my UIDocument subclass. The override reliably picks up name changes made in the cloud, e.g. renaming the document on another device. Then sometimes newURL is the final expected URL for the renamed document, i.e. something sensible from which I can extract the new name use `lastPathComponent', update my interface etc. On other occasions newURL is a document in some other directory with a last path component beginning 'purg-', e.g. purg-012fdcfbe3b3bbce6e603fdfd2f000b2cb28649e95.
- (void) presentedItemDidMoveToURL:(NSURL *) newURL;
{
[super presentedItemDidMoveToURL: newURL];
if ([(id)[self delegate] respondsToSelector:#selector(documentNameChanged:)])
{
[[self delegate] documentNameChanged: self];
}
}
The presentedItemDidMoveToURL: method does not seem to be the root cause of the problem. For example, if I don't override that method at all, but periodically check in the viewController that is looking after the open document, then sometimes after a rename fileURL will return the new name and sometimes it will return `purg-.....'. So the issue appears to be to do with how renaming is handled.
Update
As al_lea pointed out, the issue here was related to accommodatePresentedItemDeletionWithCompletionHandler:. Expanding on al_lea's answer, I added the code below to my UIDocument subclass. This fixed the issue.
- (void) accommodatePresentedItemDeletionWithCompletionHandler: (void (^) (NSError *errorOrNil)) completionHandler
{
PresentedDocument* presentedDocument = [self retain];
[presentedDocument closeWithCompletionHandler: ^(BOOL success) {
NSError* error = nil;
if (!success)
{
NSDictionary* userInfo = [NSDictionary dictionaryWithObjectsAndKeys:
#"Could not close document that is being deleted on another device",
NSLocalizedDescriptionKey, nil];
error = [NSError errorWithDomain: #"some_suitable_domain"
code: 101
userInfo: userInfo];
}
completionHandler(error); // run the passed in completion handler (required)
dispatch_async(dispatch_get_main_queue(), ^
{
[[NSNotificationCenter defaultCenter] postNotificationName: NOTIFY_presentedDocumentDeletedOnAnotherDevice
object: presentedDocument
userInfo: nil];
[presentedDocument tidyUpAfterDelete]; // app specific tidy up
[presentedDocument release];
});
}];
}
With this code in place, there are no spurious and confusing presentedItemDidMoveToURL: calls made and, in addition, the relevant object can listen for notifications of deletions on other devices.
This type of URL appears when a UIDocument is opened on local and get deleted from a remote device:
file://localhost/var/mobile/Library/Mobile%20Documents/.ubd/peer-43A0AEB6-84CE-283E-CA39-FCC4EF3BC8F8-v23/ftr/purg-
You need to close the document first before it get deleted - detect this in NSFilePresenter's accommodatePresentedItemDeletionWithCompletionHandler:

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