Method Replacement (swizzle)

language: Objective-C
license: Other

                
/* http://developer.apple.com/samplecode/MethodReplacement/listing3.html */
 
#import <AppKit/AppKit.h>
#import <objc/runtime.h>
 
@interface NSWindow (TestMethodReplacement)
- (void)TestMethodReplacement_sendEvent:(NSEvent *)event;
@end
 
@implementation NSWindow (TestMethodReplacement)
 
+ (void)load {
    if (self == [NSWindow class]) {
        // Swap the implementations of -[NSWindow sendEvent:] and -[NSWindow TestMethodReplacement_sendEvent:].
        // When the -sendEvent: message is sent to an NSWindow instance, -TestMethodReplacement_sendEvent: will
        // be called instead. Calling [self TestMethodReplacement_sendEvent:event] thus calls the original method.
        Method originalMethod = class_getInstanceMethod(self, @selector(sendEvent:));
        Method replacedMethod = class_getInstanceMethod(self, @selector(TestMethodReplacement_sendEvent:));
        method_exchangeImplementations(originalMethod, replacedMethod);
    }
}
 
- (void)TestMethodReplacement_sendEvent:(NSEvent *)event {
    if ([event type] == NSLeftMouseDown && [event modifierFlags] & NSCommandKeyMask) {
        [NSAnimationContext beginGrouping];
        [[NSAnimationContext currentContext] setDuration:1.0];
        [[self animator] setAlphaValue:0.0];
        [NSAnimationContext endGrouping];
    } else {
        // Call the original sendEvent: method, whose implementation was exchanged with our own.
        // Note:  this ISN'T a recursive call, because this method should have been called through -sendEvent:.
        NSParameterAssert(_cmd == @selector(sendEvent:));
        [self TestMethodReplacement_sendEvent:event];
    }
}
 
@end