Implement highlighting

MarkdownTextView/RegularExpressionTextStorage.swift

@@ -9,17 +9,37 @@
 import UIKit
 
 public class RegularExpressionTextStorage: NSTextStorage {
+    private struct Expression {
+        let regex: NSRegularExpression
+        let attributes: [String: AnyObject]
+    }
+    
     private let backingStore: NSMutableAttributedString
+    private var expressions = [Expression]()
+    private var defaultAttributes: [String: AnyObject] = [
+        NSFontAttributeName: UIFont.preferredFontForTextStyle(UIFontTextStyleBody)
+    ] {
+        didSet {
+            highlightRange(NSRange(location: 0, length: (backingStore.string as NSString).length))
+        }
+    }
+    
+    // MARK: API
+    
+    public func addRegularExpression(expression: NSRegularExpression, withAttributes attributes: [String: AnyObject]) {
+        expressions.append(Expression(regex: expression, attributes: attributes))
+        edited(.EditedAttributes, range: NSRange(location: 0, length: backingStore.length), changeInLength: 0)
+    }
     
     // MARK: Initialization
     
     public override init() {
-        backingStore = NSMutableAttributedString()
+        backingStore = NSMutableAttributedString(string: "", attributes: defaultAttributes)
         super.init()
     }
 
     required public init(coder aDecoder: NSCoder) {
-        backingStore = NSMutableAttributedString()
+        backingStore = NSMutableAttributedString(string: "", attributes: defaultAttributes)
         super.init(coder: aDecoder)
     }
     
@@ -42,4 +62,21 @@ public class RegularExpressionTextStorage: NSTextStorage {
         backingStore.setAttributes(attrs, range: range)
         edited(.EditedAttributes, range: range, changeInLength: 0)
     }
+    
+    public override func processEditing() {
+        let lineRange = (backingStore.string as NSString).lineRangeForRange(editedRange)
+        highlightRange(lineRange)
+        super.processEditing()
+    }
+    
+    private func highlightRange(range: NSRange) {
+        setAttributes(defaultAttributes, range: range)
+        backingStore.beginEditing()
+        for expression in expressions {
+            expression.regex.enumerateMatchesInString(backingStore.string, options: nil, range: range) { (result, _, _) in
+                self.addAttributes(expression.attributes, range: result.range)
+            }
+        }
+        backingStore.endEditing()
+    }
 }

MarkdownTextView/ViewController.swift

@@ -16,6 +16,7 @@ class ViewController: UIViewController {
         let layoutManager = NSLayoutManager()
         layoutManager.addTextContainer(textContainer)
         let textStorage = RegularExpressionTextStorage()
+        textStorage.addRegularExpression(NSRegularExpression(pattern: "\\*\\*[\\w\\d]+\\*\\*", options: nil, error: nil)!, withAttributes: [NSFontAttributeName: UIFont.boldSystemFontOfSize(17)])
         textStorage.addLayoutManager(layoutManager)
         
         let textView = UITextView(frame: CGRectZero, textContainer: textContainer)