How to load a local .CSS file & JavaScript resources using iPhone UIWebView Class
This post will cover the basic setup and creation of an application with web content for iPhone that will load local CSS files and some useful JavaScript functions. Most of these hints I found partially in different blogs and forums listed in the reference section. The idea is to collect all them together. You can use the following technique to create a more attractive application design.
Creating an application using UIWebView control is not the focus of this post. Here is a helpful beginner’s tutorial for creating an application using UIWebView. We assume that you are already familiar with this topic.
Our work will start with a little change in calling load method of the UIWebView instance. Instead of loadRequest
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[[webView graphWebView] loadRequest:requestObj];
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we use the loadHTMLString method, providing an NSString object that contains HTML code of our page as a parameter:
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[[webView graphWebView] loadHTMLString:htmlPageStr baseURL:baseURL];
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To get this page to load resources and styles correctly, you have to set up the right URL:
Initial loading screen with progress indicator
On the following reference[2] you can find a short and clear revision of the problem of displaying local images in a UIWebView using CSS. To use relative paths or files in UIWebView, you have to load the HTML into the view with the correct base URL parameter. The following example shows how to do this:
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NSString *path = [[NSBundle mainBundle] bundlePath];
NSURL *baseURL = [NSURL fileURLWithPath:path];
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And then call load method of UIWebView provide above NSURL parameter:
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[[webView graphWebView] loadHTMLString:pageStr baseURL:baseURL];
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A short explanation: An NSBundle object represents a location in the file system that groups code and resources that can be used in a program. mainBundlemethod returns the NSBundleobject that corresponds to the directory where the current application executable is located. bundlePath instance method of NSBundle returns the full pathname of the receiver’s bundle directory. NSURLclass is used to create an object which will hold the URL information. It provides a way to manipulate URLs and the resources they reference. loadHTMLStringmethod of UIWebView has parameter base URL that accept an NSURL object instead of a pathname as the file reference. Giving the above base URL to UIWebView, you can refer to your bundle’s resources directory like this:
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<img src="myimage.png">
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Or from within CSS like this:
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background-image: url(loading.gif)
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It’s important to note that resources (images, CSS and JavaScript Files) inside your application bundle are at the root of the bundle, even if you place them in an separate group (folder) in your project.
Giving the correct URL to UIWebView will allow you to refer to local resources in your page, but it does not work in all cases. If you want to use JavaScipt, some additional settings have to be done.
Second loading screen with progress indicator
Now you can use generic HTML technique to add CSS and JavaScript to the web page and displaying in a UIWebView.
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<link href="default.css" rel="stylesheet" type="text/css" />
<script type="text/javascript" src="showhide.js"></script>
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Do not forget to add your CSS and Javascript files to the xCode project (if you are using external files).
Some additional actions have to be taken before starting your application and using JavaScript functions.[3]
XCode setup (*.js) javascript as some type of source code needs to be compiled in the application. We would like to include it as a resource so I’ve solved it by doing two things:
- Select .js file and in the “Detail” view unselect the bullseye column indicating it is compiled code
- In the “Groups & files” view expand the “Targets” tree and expand the application then go to “Copy Bundle Resources” and drag the *.js files into it.
The Apple dev forums has a posted solution. [4] You need to do two things – select the .js file in your project, and turn off the checkbox that indicates that it is compiled (the “bullseye” column). If you don’t do this, you’ll get a warning in your build log about being unable to compile the file (which should be your first warning – always try to figure out and and correct any and all warnings that appear in your build).
Final screen with graph representation.
In our example we need to figure out a transparent background for UIWebView. On the parent View Container we have additional controls (buttons, labels) and already defined background. The following code will set this:
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[[webView graphWebView] setBackgroundColor:[UIColor clearColor]];</code>
[[webView graphWebView] setOpaque:NO];
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MentorMateDemoJS is a simple application example which uses the settings described above. It is a view-based application that shows a graphical representation of some data. Application behavior consists of a predefined call with formatted data to Vvidget Service[5] for graph generation. The service returns an image that is loaded in UIWebView Design Resource. The update button is added to resend the graph request and update view.
The Problem: Graph image requires some time for loading.
Our Decision: Notify user of graph loading process by showing a progress bar during load time.
To achieve this, we use UIWebView with local resource of two JavaScript functions. One to show/hide notification messages and the other to visualize a progress bar during loading time. In the provided sources you can find all these steps implemented.
Sources of the example iPhone application
- iPhone SDK Articles, UIWebView Tutorial
- iPhone Development Blog, UIWebView – Loading External Images and CSS
- StackOverflow, iPhone UIWebView local resources using Javascript and handling on orientationChange
- Developer Forum, UIWebView and JavaScript
