langs a-z

Task/Delegates/Objective-C/delegates.m

@@ -0,0 +1,76 @@
+#import <Foundation/Foundation.h>
+
+@interface Delegator : NSObject {
+
+    id delegate;
+}
+
+- (id)delegate;
+- (void)setDelegate:(id)obj;
+- (NSString *)operation;
+
+@end
+
+@implementation Delegator
+
+- (id)delegate {
+
+    return delegate;
+}
+
+- (void)setDelegate:(id)obj {
+
+    delegate = obj; // Weak reference
+}
+
+- (NSString *)operation {
+
+    if ([delegate respondsToSelector:@selector(thing)])
+        return [delegate thing];
+
+    return @"default implementation";
+}
+
+@end
+
+// Any object may implement these
+@interface NSObject (DelegatorDelegating)
+
+- (NSString *)thing;
+
+@end
+
+@interface Delegate : NSObject
+
+// Don't need to declare -thing because any NSObject has this method
+
+@end
+
+@implementation Delegate
+
+- (NSString *)thing {
+
+    return @"delegate implementation";
+}
+
+@end
+
+// Example usage
+// Memory management ignored for simplification
+int main() {
+
+    // Without a delegate:
+    Delegator *a = [[Delegator alloc] init];
+    NSLog(@"%d\n", [[a operation] isEqualToString:@"default implementation"]);
+
+    // With a delegate that does not implement thing:
+    [a setDelegate:@"A delegate may be any object"];
+    NSLog(@"%d\n", [[a operation] isEqualToString:@"delegate implementation"]);
+
+    // With a delegate that implements "thing":
+    Delegate *d = [[Delegate alloc] init];
+    [a setDelegate:d];
+    NSLog(@"%d\n", [[a operation] isEqualToString:@"delegate implementation"]);
+
+    return 0;
+}