Loading UIWebView From Background Fetch

Question

I am using a UIWebView in my app to load the contents of a website. I then use javascript to log into the website, and then I parse the contents of the page after I've logged in to grab the data I need. I do this every 5 minutes, which works fine in the foreground. However, when I background the app, I make a call to the UIViewController that holds the UIWebView and I hit the method that loads the URL into the UIWebView, but nothing happens after that.

I am fairly sure that the UIViewController must be active to update the UIWebView, but is there a way around this? Checking this data in the background is really the entire point of the app.

EDIT

jakepeterson - Based on your code, I tried to subclass a UIWebView starting in Swift. This is as far as I got:

    class CustomWebView: UIWebView, UIWebViewDelegate
{
    var webView: UIWebView
    var requestURL: NSURL
    var urlRequest: NSURLRequest

    init()
    {
        webView = UIWebView()
        requestURL = NSURL(string: "http://www.google.com")
        urlRequest = NSURLRequest(URL: requestURL)

        super.init(frame: CGRectMake(0, 0, 100, 100))
        webView.delegate = self
        webView.addSubview(webView.window)
        webView.loadRequest(request)
    }

    func webViewDidFinishLoad(sender: UIWebViewDelegate)
    {
        //Do stuff
    }
}

I am still not hitting the webViewDidFinishLoad delegate method. I think it has to do possibly with this line:

webView.addSubview(webView.window)

In your code you have self.view but that doesn't show up as an available option.

UPDATE

Here is what I am doing now and the delegates are now getting triggered:

import UIKit

class CustomWebView: UIWebView
{
    var uiView = UIView()

    init(frame: CGRect)
    {
        super.init(frame: frame)
        self.delegate = self
    }

    convenience init(frame:CGRect, request:NSURLRequest)
    {
        self.init(frame: frame)
        uiView.addSubview(self)
        loadRequest(request)
    }    
}

extension CustomWebView: UIWebViewDelegate
{
    func webViewDidStartLoad(webView: UIWebView!)
    {
        println("webViewDidStartLoad")
    }

    func webViewDidFinishLoad(webView: UIWebView)
    {
        println("webViewDidFinishLoad")
    }

    func webView(webView: UIWebView!, didFailLoadWithError error: NSError!)
    {
        println("An error occurred while loading the webview")
    }
}

jakenberg · Accepted Answer · 2014-07-03 21:56:04Z

2

Here's an example of how the UIWebView class can be used objectively with asynchronous logic:

- (id)init
{
    self = [super init];
    if (self)
    {
        self.webView = [[UIWebView alloc] init];
        self.webView.delegate = self;
        [self.view addSubview:self.webView];

        self.activityIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
        [self.view addSubview:self.activityIndicator];
    }

    return self;
}

- (id)initWithUrl:(NSURL *)url
{
    self = [self init];
    if (self)
    {
        NSURLRequest *request = [NSURLRequest requestWithURL:url];
        [self.webView loadRequest:request];
        [self.activityIndicator startAnimating];
    }

    return self;
}

#pragma mark - UIWebViewDelegate

- (void)webViewDidFinishLoad:(UIWebView *)webView
{
    [self.activityIndicator stopAnimating];
}

- (void)webView:(UIWebView *)webView didFailLoadWithError:(NSError *)error
{
    [self.activityIndicator stopAnimating];

    NSLog(@"An error occurred while loading. (error: %@)", error);

    // Alert the user
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Oops" message:@"Dude... we messed up. This web page can't be loaded at this time." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alertView show];
}

Why does this work?

Because you are depending on the delegate methods of UIWebViewDelegate to tell you when the UIWebView has finished loading. I included the error delegate method as a bonus.

The example here is using a UIActivityIndicatorView class, which is designed for use in asynchronous tasks. By following this same implementation style, you can replace the activityIndicator with virtually anything you plan to act on the results of the UIWebView pragmatically with.

Good luck

UPDATE

Swift is a whole other beast. Your swift class has a plethora of errors in it. This is how I would re-write what I originally gave you in ObjC in Swift:

import UIKit

class CustomWebView: UIWebView {

    var activityIndicator:UIActivityIndicatorView

    init(frame: CGRect) {
        self.activityIndicator = UIActivityIndicatorView(activityIndicatorStyle: UIActivityIndicatorViewStyle.Gray)
        super.init(frame: frame)
        self.delegate = self
    }

    convenience init(frame:CGRect, request:NSURLRequest) {
        self.init(frame: frame)
        loadRequest(request)
    }

}

extension CustomWebView: UIWebViewDelegate {

    func webViewDidFinishLoad(webView: UIWebView) {
        self.activityIndicator.stopAnimating()
    }

    func webView(webView: UIWebView!, didFailLoadWithError error: NSError!) {
        self.activityIndicator.stopAnimating()

        println("An error occurred while loading the webview")
    }

}

edited Jul 3, 2014 at 21:56

answered Jul 2, 2014 at 2:11

jakenberg

2,11320 silver badges38 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

PretzelJesus Over a year ago

This doesn't work for me. I edited my original post to explain what I am seeing.

PretzelJesus Over a year ago

Thanks for converting that to Swift. It helped me understand what you were doing a bit better. When I run your code though I am unable to set the NSURLRequest. Every time I try to initialize it with one I get an "EXC_BAD_ACCESS" error on the "self.request = newValue" line.

PretzelJesus Over a year ago

I'm extremely new so bear with my while I try and debug. I added the line "println("(newValue)") to where the NSURLRequest is being set. I get this in the console window: "<NSURLRequest: 0xb30ab40> { URL: google.com, headers: (null) }". I get this hundreds of times. So I wonder if it gets stuck in a loop and runs out of memory for some reason...

PretzelJesus Over a year ago

Ok it no longer crashes, but now I am back to my original issue in that the delegate events never fire, specifically the webViewDidFinishLoad event.

jakenberg Over a year ago

Are you passing in a non-nil request in your initializer?

|

PretzelJesus · Accepted Answer · 2014-07-04 18:03:45Z

0

It appears that the trick I found of adding the control to a UIView to get the delegates to fire only works in the foreground. So for anyone checking this question there currently does not seem to be a way to do this in the background.

answered Jul 4, 2014 at 18:03

PretzelJesus

8993 gold badges11 silver badges22 bronze badges

1 Comment

ninjaneer Over a year ago

is that also true for WKWebView?

Collectives™ on Stack Overflow

Loading UIWebView From Background Fetch

2 Answers 2

8 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

8 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related