UIWebView CSS injection using JavaScript

Question

I'm trying to inject a local css file into an UIWebView that finished loading website such as google etc.

I'm trying with JavaScript but with no success.

- (void)webViewDidFinishLoad:(UIWebView *)webView {
    NSString *cssPath = [[NSString alloc] initWithString:[[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"styles.css"]];
    NSURL *baseURL = [NSURL fileURLWithPath:cssPath];

    NSString *js = [NSString stringWithFormat:@"var fileref = document.createElement('link');
                    fileref.setAttribute('rel', 'stylesheet');
                    fileref.setAttribute('type', 'text/css');
                    fileref.setAttribute('href', %@);", baseURL];

    [webView stringByEvaluatingJavaScriptFromString:js];
}

Thanks,

Answer 1

To inject javascript into a web view you must explicitly write in the html.

An example of this is here where I wrote in a javascript scrollTo function:

- (void)webViewDidFinishLoad:(UIWebView *)webView {
 [webView stringByEvaluatingJavaScriptFromString:@"var script = document.createElement('script');"  
 "script.type = 'text/javascript';"  
 "script.text = \"function myFunction() { "  
 "window.scrollTo(100,100)"
 "}\";"  
 "document.getElementsByTagName('head')[0].appendChild(script);"];  

 [webView stringByEvaluatingJavaScriptFromString:@"myFunction();"];}

This code writes the entire script tags and the myFunction into the head of the HTML

Answer 2

I had a similar need. I have local html files in the bundle that I wanted to change css attributes programatically. Since you can not change files in the bundle, I wanted to inject my css at load time from variables in the app.

The code below demonstrates the technique, just substitute your method for getting the css, i.e. read from a file, plist, code, or db.

- (void)webViewDidFinishLoad:(UIWebView *)webView
{
    NSString* css = @"\"@font-face { font-family: 'Chalkboard'; src: local('ChalkboardSE-Regular'); } body { background-color: #F0F0FC; color: #572B00; font-family: Chalkboard;} a { color: #A00; text-decoration: none;}\"";
    NSString* js = [NSString stringWithFormat:
                @"var styleNode = document.createElement('style');\n"
                 "styleNode.type = \"text/css\";\n"
                 "var styleText = document.createTextNode('%@');\n"
                 "styleNode.appendChild(styleText);\n"
                 "document.getElementsByTagName('head')[0].appendChild(styleNode);\n",css];
    NSLog(@"js:\n%@",js);
    [self.webView stringByEvaluatingJavaScriptFromString:js];
}

Answer 3

I would suggest you to create a js file and add to your project file.

NSString *filePath = [[NSBundle mainBundle] pathForResource:@"test" ofType:@"js"];

NSData *fileData = [NSData dataWithContentsOfFile:filePath]; 

NSString *jsString = [[NSString alloc] initWithData:fileData encoding:NSUTF8StringEncoding];

and you know how to call js in html file. this is the simplest and clean way to do it.