iOS 的 runtime

Runtime

运行时的使用:

1. KVO , KVC

2. 运行过程中交换两个方法的实现,改系统的方法.

　　例如:  当一个做了几年的项目要从iOS6适配到iOS7时,要把之前的图片全部换掉,可通过扩展UIImage 实现它的分类.补充一个类方法imageWithName: name.然后将系统的imageName:方法与imageWithName:name 的方法在运行时换掉,而不用修改其他代码.

#import "UIImage+Extension.h"
#import <objc/runtime.h>

@implement UIImage(Extension)

+(void) load
{
    Method otherMethod = class_getClassMethod([UIImage class],@selector(imageWithName:));
    Method originMethod = class_getClassMethod([UIImage class],@selector(imageNamed:));
    //交换两个方法的实现
    method_exchangeImplementations(otherMethod, originMethod);
}

+ (UIImage *) imageWithName:(NSString *) name
{
    BOOL ios7 = [[UIDevice currentDevice].systemVersion floatValue] >= 7.0;
    UIImage * image = nil;
    if (ios7)
    {
        NSString * newName = [name stringByAppendingString:@"_os7"];
        image = [UIImage imageWithName:newName];
        }
    if (image ==nil)
    {
        image = [UIImage imageWithName: name];
    }
    return image;
}
@end