Highlighting Text in a UIWebView

As a continuation of this post I wanted to share a few things about how I solved the problem of working w/ text in a UIWebView.

I did it mostly thru running Javascript via the stringByEvaluatingJavaScriptFromString: method on the UIWebView which I extended thru another class (e.g., MyWebView).

There’s a few key actions:

1. override canPerformAction:withSender: to prevent the built-in menu
2. create the JavaScript to get aspects of the selection in the web view
3. run the JavaScript to get the info into your app

1. override canPerformAction:withSender: to prevent the built-in menu

Also, I override the canPerformAction:withSender: method to avoid the Copy/Cut/Paste menu from popping up. This is called when the user holds their finger down to select text in a webview. This gives you two things: 1. the chance to prevent the Copy/Cut/Paste menu and 2. it’s the notification that they are selecting text.

So how do you get what they selected?

2. create the JavaScript to get aspects of the selection in the web view

I saved my Javascript in separate files so I can read in the text and run it in the method (mentioned above). The following Javascript returns what is selected…

function f() {
  var txt = window.getSelection();
  return (txt.anchorOffset + '|' + txt.anchorNode.textContent + '|' + txt.focusOffset + '|' + txt.focusNode.textContent);
}
f();

The values are:

• txt.anchorOffset – the offset, in characters, where the selection begins
• txt.anchorNode.textContent – the text of that node (e.g., paragraph based on <p>)
• txt.focusOffset – the offset, in characters, where the selection ends
• txt.focusNode.TextContent – the text of that node

B/c the selection may go across nodes (e.g., selection starts in one paragraph and into another), you use anchor and focus objects.

From this you can determine what text is selected IF you also have the content the webview is rendering (the html or whatever). And based on that, you can insert font or style tags to alter the text (e.g., highlight, bold, etc.). If you don’t have the content, you can still get what they are selecting, but you probably can’t do anything w/ it in the web view.

3. run the JavaScript to get the info into your app

I store the above JavaScript in a file called getSelection.txt in the project. To run it, I have the following method…

-(NSString*)webviewGetSelection
{
NSString *js = [UtilString contentsOfFile:@"getSelection" withExt:@"txt"];
NSString *result = [self stringByEvaluatingJavaScriptFromString:js];
NSLog(@"selected: %@", result);
return result;
}

You as a result you might get:
0|Here is a paragraph.|3|Here is a paragraph.

This means they selected the 0-3 characters of that paragraph which works out to be the word: Here.

Another example result might be:
4|The middle word.|3|The first word.

This means the 4th character of the paragraph comprised of ‘The middle word.’ thru the 3rd character of the paragraph comprised of ‘The first word.’
This works out to be that they selected ‘middle word. The’

However, there may be a paragraph between those two paragraphs. If so, that entire paragraph is included in the selection.

If you have the content of the web view, you can search for the first paragraph and the second and get everything btwn them too. Otherwise, you’ll need to get more into the anchorNode/focusNode and/or create JavaScript to count the parentNodes and such to determine where the text is.
Some other useful Javascript methods are:

• self.find(<string>); – navigates to the next occurrence of a string
• window.pageYOffset; – basically tells you the scroll position of the webview
• window.scrollTo(x, y); – allows you to effectively set the scroll position

I hope this helps. Feel free to comment/improve/etc.

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