XXNibBridge.m

// XXNibBridge.m
// Version 2.2
//
// Copyright (c) 2015 sunnyxx ( http://github.com/sunnyxx )
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

#import "XXNibBridge.h"
#import <objc/runtime.h>

@interface XXNibBridgeImplementation : NSObject
/// `NS_REPLACES_RECEIVER` attribute is a must for right ownership for `self` under ARC.
- (id)hackedAwakeAfterUsingCoder:(NSCoder *)decoder NS_REPLACES_RECEIVER;
@end

@implementation XXNibBridgeImplementation

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        SEL originalSelector = @selector(awakeAfterUsingCoder:);
        SEL swizzledSelector = @selector(hackedAwakeAfterUsingCoder:);
        Method originalMethod = class_getInstanceMethod(UIView.class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(self, swizzledSelector);
        if (class_addMethod(UIView.class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))) {
            class_replaceMethod(UIView.class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
        } else {
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}

- (id)hackedAwakeAfterUsingCoder:(NSCoder *)decoder {
    if ([self.class conformsToProtocol:@protocol(XXNibBridge)] && ((UIView *)self).subviews.count == 0) {
        // "self" is placeholder view for this moment, replace it.
        return [XXNibBridgeImplementation instantiateRealViewFromPlaceholder:(UIView *)self];
    }
    return self;
}

+ (UIView *)instantiateRealViewFromPlaceholder:(UIView *)placeholderView {
    
    // Required to conform `XXNibConvension`.
    UIView *realView = [[placeholderView class] xx_instantiateFromNib];

    realView.tag = placeholderView.tag;
    realView.frame = placeholderView.frame;
    realView.bounds = placeholderView.bounds;
    realView.hidden = placeholderView.hidden;
    realView.clipsToBounds = placeholderView.clipsToBounds;
    realView.autoresizingMask = placeholderView.autoresizingMask;
    realView.userInteractionEnabled = placeholderView.userInteractionEnabled;
    realView.translatesAutoresizingMaskIntoConstraints = placeholderView.translatesAutoresizingMaskIntoConstraints;
    
    // Copy autolayout constrains.
    if (placeholderView.constraints.count > 0) {
        
        // We only need to copy "self" constraints (like width/height constraints)
        // from placeholder to real view
        for (NSLayoutConstraint *constraint in placeholderView.constraints) {
            
            NSInvocation *firstItemInvocation = [self invocationForTarget:constraint withSelector:@"_setFirstItem:attribute:"];
            [firstItemInvocation setArgument:&realView atIndex:2];
            long long firstAttribute = constraint.firstAttribute;
            [firstItemInvocation setArgument: &firstAttribute atIndex:3];
            
            NSInvocation *secondItemInvocation = [self invocationForTarget:constraint withSelector:@"_setSecondItem:attribute:"];
            [secondItemInvocation setArgument:&realView atIndex:2];
            long long secondAttribute = constraint.secondAttribute;
            [secondItemInvocation setArgument: &secondAttribute atIndex:3];
            
            // "Height" or "Width" constraint
            // "self" as its first item, no second item
            if (!constraint.secondItem) {
                if ([self isHigherThanIOS10]) {
                    [firstItemInvocation invoke];
                } else {
                    [constraint setValue:realView forKey:@"firstItem"];
                }
                [realView addConstraint:constraint];
            }
            // "Aspect ratio" constraint
            // "self" as its first AND second item
            else if ([constraint.firstItem isEqual:constraint.secondItem]) {
                if ([self isHigherThanIOS10]) {
                    [firstItemInvocation invoke];
                    [secondItemInvocation invoke];
                } else {
                    [constraint setValue:realView forKey:@"firstItem"];
                    [constraint setValue:realView forKey:@"secondItem"];
                }
                [realView addConstraint:constraint];
            }
        }
    }
    
    return realView;
}

+ (Boolean)isHigherThanIOS10 {
    return [[[UIDevice currentDevice] systemVersion] floatValue] >= 10.0f;
}

+ (NSInvocation *)invocationForTarget:(id)target
                         withSelector:(NSString *)aSelectorName {
    SEL methodSelector = NSSelectorFromString(aSelectorName);
    NSMethodSignature *methodSignature = [NSLayoutConstraint instanceMethodSignatureForSelector:methodSelector];
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];
    [invocation setTarget:target];
    [invocation setSelector:methodSelector];
    
    return invocation;
}

@end