UIViewController+SegueData.m

UIViewController+SegueData.m

//
//  UIViewController+SegueData.h
//  SegueDataPassing - Helper method for performing a segue and passing data to
//                     the destination view controller.
//
//  Created by John Hurliman on 10/21/14.
//  Copyright (c) 2014 John Hurliman. Released under the MIT license.
//  http://opensource.org/licenses/MIT
//

#import <UIKit/UIKit.h>

@interface UIViewController (SegueData)

/**
 * Getter for the segueData property. This property is set on the destination
 * UIViewController when calling performSegueWithIdentifier:data:.
 */
- (id)segueData;

/**
 * Setter for the segueData property. This is called automatically when calling
 * performSegueWithIdentifier:data: and generally does not need to called
 * explicitly.
 */
- (void)setSegueData:(id)data;

/**
 * Perform a segue and set the segueData property on the destination
 * UIViewController to the data value.
 */
- (void)performSegueWithIdentifier:(NSString *)identifier data:(id)data;

@end





//
//  UIViewController+SegueData.m
//  SegueDataPassing
//
//  Created by John Hurliman on 10/21/14.
//  Copyright (c) 2014 John Hurliman. Released under the MIT license.
//  http://opensource.org/licenses/MIT
//

#import "UIViewController+SegueData.h"
#import <objc/runtime.h>
#import <objc/message.h>

// Unique identifiers for associated objects
static char const * const SegueMethodSwizzledKey = "SegueMethodSwizzledKey";
static char const * const SegueNameKey = "SegueNameKey";
static char const * const SegueDataToPassKey = "SegueDataToPassKey";
static char const * const SegueDataKey = "SegueDataKey";

// Method swizzling helper for replacing prepareForSegue:sender:
void MethodSwizzle(Class c, SEL orig, SEL new) {
    Method origMethod = class_getInstanceMethod(c, orig);
    Method newMethod = class_getInstanceMethod(c, new);
    if(class_addMethod(c, orig, method_getImplementation(newMethod), method_getTypeEncoding(newMethod)))
        class_replaceMethod(c, new, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
    else
        method_exchangeImplementations(origMethod, newMethod);
}

@implementation UIViewController (SegueData)

- (id)segueData
{
    return objc_getAssociatedObject(self, SegueDataKey);
}

- (void)setSegueData:(id)data
{
    objc_setAssociatedObject(self, SegueDataKey, data, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (void)performSegueWithIdentifier:(NSString *)identifier data:(id)data
{
    // Store the segue name and the data to be passed as instance variables of
    // the current view controller
    objc_setAssociatedObject(self, SegueNameKey, identifier, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    objc_setAssociatedObject(self, SegueDataToPassKey, data, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    
    // Replace the prepareForSegue:sender: method with our own if we haven't yet
    NSNumber *swizzled = objc_getAssociatedObject(self, SegueMethodSwizzledKey);
    if (!swizzled || !swizzled.boolValue) {
        objc_setAssociatedObject(self, SegueMethodSwizzledKey, @(YES), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
        MethodSwizzle(UIViewController.class, @selector(prepareForSegue:sender:), @selector(myPrepareForSegue:sender:));
    }
    
    // Perform the actual segue
    [self performSegueWithIdentifier:identifier sender:self];
}

- (void)myPrepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    NSString *segueName = objc_getAssociatedObject(self, SegueNameKey);
    
    // Check if this is our segue
    if ([segue.identifier isEqualToString:segueName]) {
        UIViewController *dest = segue.destinationViewController;
        dest.segueData = objc_getAssociatedObject(self, SegueDataToPassKey);
        
        // Release temporary pointers
        objc_setAssociatedObject(self, SegueDataToPassKey, nil, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
        objc_setAssociatedObject(self, SegueNameKey, nil, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    
    // (Unintuitively) calls the original method
    [self myPrepareForSegue:segue sender:sender];
}

@end