WordProcessorDelegate

Author: yakovmanshin

BirdProcessor/UI/ViewController.m

@@ -1,7 +1,7 @@
 #import "BirdProcessor-Swift.h"
 #import "ViewController.h"
 
-@interface ViewController ()
+@interface ViewController () <WordProcessorDelegate>
 
 @property (nonatomic) WordProcessor *wordProcessor;
 
@@ -17,6 +17,7 @@ - (void)viewDidLoad {
 
     id<StringManipulatorProtocol> stringManipulator = [[StringManipulator alloc] init];
     self.wordProcessor = [[WordProcessor alloc] initWithStringManipulator:stringManipulator];
+    self.wordProcessor.delegate = self;
 }
 
 - (IBAction)didTapProcessButton:(UIButton *)sender {
@@ -27,4 +28,18 @@ - (IBAction)didTapProcessButton:(UIButton *)sender {
     [self.resultLabel setText:processingResult];
 }
 
+// We’re only interested in the third method, but the compiler requires all three:
+
+- (void)wordProcessor:(WordProcessor *)processor didBeginProcessingInput:(NSString *)string {
+    
+}
+
+- (void)wordProcessor:(WordProcessor *)processor didFinishProcessingInput:(NSString *)string {
+    
+}
+
+- (void)wordProcessor:(WordProcessor *)processor didEncounterError:(NSString *)error {
+    // Show an error alert
+}
+
 @end

BirdProcessor/WordProcessor/WordProcessor.swift

@@ -3,11 +3,19 @@
 
     private let stringManipulator: any StringManipulatorProtocol
 
+    @objc weak var delegate: (any WordProcessorDelegate)?
+    
     @objc init(stringManipulator: any StringManipulatorProtocol) {
         self.stringManipulator = stringManipulator
     }
 
     @objc func processInputString(_ string: String) -> String {
+        delegate?.wordProcessor(self, didBeginProcessingInput: string)
+        // This runs *after* the resulting string is constructed
+        // but *before* control is returned to the caller—
+        // in other words, when processing is truly finished
+        defer { delegate?.wordProcessor(self, didFinishProcessingInput: string) }
+        
         let isEmpty = stringManipulator.isEmpty(string)
         let isEmptyResult = isEmpty ? "is" : "is not"
 
@@ -16,6 +24,10 @@
             "\(numberOfWords) word(s) and "
         } else { "" }
 
+        if numberOfWordsResult.isEmpty {
+            delegate?.wordProcessor(self, didEncounterError: "Cannot count words")
+        }
+        
         let numberOfCharacters = stringManipulator.numberOfCharacters(in: string)
         let numberOfCharactersResult = "\(numberOfCharacters) character(s)"
 

BirdProcessor/WordProcessor/WordProcessorDelegate.swift

@@ -0,0 +1,5 @@
+@objc protocol WordProcessorDelegate {
+    func wordProcessor(_ processor: WordProcessor, didBeginProcessingInput string: String)
+    func wordProcessor(_ processor: WordProcessor, didFinishProcessingInput string: String)
+    func wordProcessor(_ processor: WordProcessor, didEncounterError error: String)
+}

README.md

@@ -9,5 +9,5 @@ You’ll find different stages of the project in separate branches.
 * [x] Implement the Objective-C protocol (`StringManipulatorProtocol`) in the Swift object (`StringManipulator`)
 * [x] Fix the crash that occurs when the non-implemented optional method is called
 * [x] Replace `WordProcessor` with a Swift version and use the better way to handle the optional method
-* [ ] Declare the `WordProcessorDelegate` protocol in Swift and implement it in Objective-C (`ViewController`)
+* [x] Declare the `WordProcessorDelegate` protocol in Swift and implement it in Objective-C (`ViewController`)
 * [ ] Mark the protocol’s methods as `optional` and remove the unneeded method implementations