Displaying Web Content

If your user interface includes a UIWebView object, you can display local content or content that is loaded from the network. When loading local content, you can either create the content dynamically or load it from a file and display it using the loadData:MIMEType:textEncodingName:baseURL: or loadHTMLString:baseURL: method. The method in Listing 3-1 uses the loadData:MIMEType:textEncodingName:baseURL: method to load the contents of a PDF file into a web view.

Listing 3-1  Loading a local PDF file into the web view

- (void)viewDidLoad {
    [super viewDidLoad];
 
    NSString *thePath = [[NSBundle mainBundle] pathForResource:@"iPhone_User_Guide" ofType:@"pdf"];
    if (thePath) {
        NSData *pdfData = [NSData dataWithContentsOfFile:thePath];
        [(UIWebView *)self.view loadData:pdfData MIMEType:@"application/pdf"
            textEncodingName:@"utf-8" baseURL:nil];
    }
}

To load content from the network, you create an NSURLRequest object and pass it to the loadRequest: method of your web view. 

[self.myWebView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.apple.com/"]]];

Because loading a web resource might take some time, you might display an activity indicator to indicate that the load is underway. You can do this by assigning a delegate to the web view and implementing the UIWebViewDelegate methods, as in Listing 3-2. The delegate displays an activity indicator when the load starts and hides it when the load ends. If there is a problem with the load, it creates an HTML error message and, using the loadHTMLString:baseURL: method, loads it into the web view for display.

Listing 3-2  The web-view delegate managing network loading

- (void)webViewDidStartLoad:(UIWebView *)webView
{
    // starting the load, show the activity indicator in the status bar
    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
}
 
- (void)webViewDidFinishLoad:(UIWebView *)webView
{
    // finished loading, hide the activity indicator in the status bar
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}
 
- (void)webView:(UIWebView *)webView didFailLoadWithError:(NSError *)error
{
    // load error, hide the activity indicator in the status bar
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
 
    // report the error inside the webview
    NSString* errorString = [NSString stringWithFormat:
                             @"<html><center><font size=+5 color='red'>An error occurred:<br>%@</font></center></html>",
                             error.localizedDescription];
    [self.myWebView loadHTMLString:errorString baseURL:nil];
}

If, after initiating a network-based load request, you must release your web view for any reason, you must cancel the pending request before releasing the web view. You can cancel a load request using the web view’s stopLoading method. A typical place to include this code would be in the viewWillDisappear: method of the owning view controller. To determine if a request is still pending, you can check the value in the web view’s loading property. Listing 3-3 illustrates how you might do this.

Listing 3-3  Stopping a load request when the web view is to disappear

- (void)viewWillDisappear:(BOOL)animated
{
    if ( [self.myWebView loading] ) {
        [self.myWebView stopLoading];
    }
    self.myWebView.delegate = nil;    // disconnect the delegate as the webview is hidden
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}

The loadRequest: example is taken from the UICatalog sample code project.



© 2011 Apple Inc. All Rights Reserved. (Last updated: 2011-03-07)

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