NSTimer with UIWebView - feasibility

Question

Currently I'm still reading through some document and tutorial for NSTimer. From my current understanding, We call the timer and give it a method so that it will repeat itself. Then an idea struck me.(im working on other app proj)

What I plan to do

• implement UIWebView
• implement NSTimer(maybe 0.5sec) within the UIWebView with a method that check the UIWebView current url (absolutestring) and if it's not what I specified, it will redirect the url.

I have the code that I want to implement, the purpose is to rectify my knowledge on UIWebView and NSTimer and see if its plausible before I start working on it.( I'm still reading on documents. So would like to learn more and try out more before working on it)

The confusing part to me now is that, is my method compatible with NSTimer? Will it be plausible to use NSTimer within a UIWebView viewDidLoad method? Will there be a memory overload/crash due to the app constantly running the method every 0.5sec?

e.g of NSTimer (correct me if I'm wrong. But since I want it to be running forever as long as the user are in the UIWebView, I will only require this code set and not include NSRunLoop)

NSTimer *t = [NSTimer scheduledTimerWithTimeInterval: 2.0
                      target: self
                      selector:@selector(onTick:)
                      userInfo: nil repeats:NO];

-(void)onTick:(NSTimer *)timer {
   //do smth
}

EDIT2- @Robert Ryan, this is the code I'm using.(which work just now when i first changed to this) **(If i blocked out range2 section, then the error domain error-999 stopped. but the view still doesn't load)

     - (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
    NSString *currentURL = [[request URL] absoluteString];
    NSRange range1= [currentURL rangeOfString:@"news"];
    NSRange range2= [currentURL rangeOfString:@"pdf"];
    if (range1.location == NSNotFound)
    {
        NSURL *url = [NSURL URLWithString:@"http://www.imc.jhmi.edu/news.html"];
        [webView loadRequest:[NSURLRequest requestWithURL:url]];

        return NO; //no to this if its not found.
    }
    if(range2.location==NSNotFound)
    {
        NSURL * url = [NSURL URLWithString:@"http://www.imc.jhmi.edu/news.html"];
        [webView loadRequest:[NSURLRequest requestWithURL:url]];
        return NO; //no to this if its not found
    }

    return YES; //everything else ok

}

EDIT3 - if i combine the both NSRange range1 and range2 into 1 statement then it work again(hopefully it will still work after an hour. xD)

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
    NSString *currentURL = [[request URL] absoluteString];
    NSRange range1= [currentURL rangeOfString:@"news"];
    NSRange range2= [currentURL rangeOfString:@"pdf"];
    if (range1.location == NSNotFound & range2.location==NSNotFound)
    {
        NSURL *url = [NSURL URLWithString:@"http://www.imc.jhmi.edu/news.html"];
        [webView loadRequest:[NSURLRequest requestWithURL:url]];

        return NO;
    }
return YES;
}

Answer 1

If what you want is to make sure that the user does not navigate to other urls, you could add the following

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
    if ([[request.URL absoluteString] isEqualToString:@"http://YourAllowableURL1.com"]) {
        return YES;
    }

    if ([[request.URL absoluteString] isEqualToString:@"http://YourAllowableURL2.com"]) {
        return YES;
    }

    return NO;// user will not be able to go to any other urls
}

You can also specify a list of allowable URLs and make sure to return YES for only these URLs

Answer 2

The use of NSTimer's to determine an attempt to go to an "unapproved" web site is not quite what you want. The shouldStartLoadWithRequest will let you cancel the current request if the URL isn't acceptable. It does not, though, allow you to change the URL to effect a redirect. If you really want to redirect, you could initiate a brand new request, perhaps after a little delay, e.g.,

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
    NSString *currentURL = [[request URL] absoluteString];
    NSRange range = [currentURL rangeOfString:@"imc.jhmi.edu"];

    if (range.location == NSNotFound)
    {
        double delayInSeconds = 0.1;
        dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
        dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
            NSURL *url = [NSURL URLWithString:@"http://www.imc.jhmi.edu/news.html"];
            [webView loadRequest:[NSURLRequest requestWithURL:url]];
        });

        return NO;
    }

    return YES;
}

It actually looks like you don't have to wait, you can actually just initiate the new request immediately, but it doesn't seem right to do so before the previous shouldStartLoadWithRequest has completed. But if you wanted to do that, it obviously would be:

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
    NSString *currentURL = [[request URL] absoluteString];
    NSRange range = [currentURL rangeOfString:@"imc.jhmi.edu"];

    if (range.location == NSNotFound)
    {
        NSURL *url = [NSURL URLWithString:@"http://www.imc.jhmi.edu/news.html"];
        [webView loadRequest:[NSURLRequest requestWithURL:url]];

        return NO;
    }

    return YES;
}

Personally, I wouldn't redirect the user at all, but at most pop up a UIAlertView that tells them they have to stay on this site, but this is up to you:

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
    NSLog(@"%s %@", __FUNCTION__, request);

    NSString *currentURL = [[request URL] absoluteString];
    NSRange range = [currentURL rangeOfString:@"imc.jhmi.edu"];

    if (range.location == NSNotFound)
    {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"This app only follows links within the www.imc.jhmi.edu site." 
                                                        message:nil 
                                                       delegate:nil 
                                              cancelButtonTitle:@"Ok" 
                                              otherButtonTitles:nil];
        [alert show];
        // [alert release]; // use in non-ARC
        return NO;
    }

    return YES;
}