一个iOS开发项目无外乎就是纯代码布局、xib或SB布局。那么如何实现两个方式的字体大小适配呢？
字体大小适配------纯代码
定义一个宏定义如下
#define SizeScale (SCREEN_WIDTH == 414 ? 1 : 0.83)(我用的7P当做1)

#define SizeScale (SCREEN_WIDTH != 414 ? 1 : 1.2)

#define kFont(value) [UIFont systemFontOfSize:value * SizeScale]

在宏中的1.2是在plus下的大小放大比例,可以根据自己的实际情况来调整。
纯代码中设置字体大小通过使用这个宏来实现整体适配
字体大小适配------xib或SB
字体大小适配无外乎就是设置UIButton、UILabel、UITextView、UITextField的字体大小
通过创建这几个的类目来实现（Runtime方式的黑魔法method swizzling）
废话不多说，直接上代码：

.h

#import <UIKit/UIKit.h>
#import <objc/runtime.h>

/**
 *  button
 */
@interface UIButton (MyFont)

@end


/**
 *  Label
 */
@interface UILabel (myFont)

@end

/**
 *  TextField
 */

@interface UITextField (myFont)

@end

/**
 *  TextView
 */
@interface UITextView (myFont)

@end

.m

#import "UIButton+MyFont.h"

//不同设备的屏幕比例(当然倍数可以自己控制)
#define SizeScale (SCREEN_WIDTH == 414 ? 1 : 0.83) // 1:1.2

@implementation UIButton (MyFont)

+ (void)load{
    Method imp = class_getInstanceMethod([self class], @selector(initWithCoder:));
    Method myImp = class_getInstanceMethod([self class], @selector(myInitWithCoder:));
    method_exchangeImplementations(imp, myImp);
}

- (id)myInitWithCoder:(NSCoder*)aDecode{
    [self myInitWithCoder:aDecode];
    if (self) {
        
        //部分不像改变字体的 把tag值设置成333跳过
        if(self.titleLabel.tag != 333){
            CGFloat fontSize = self.titleLabel.font.pointSize;
            self.titleLabel.font = [UIFont systemFontOfSize:fontSize * SizeScale];
        }
    }
    return self;
}

@end


@implementation UILabel (myFont)

+ (void)load{
    Method imp = class_getInstanceMethod([self class], @selector(initWithCoder:));
    Method myImp = class_getInstanceMethod([self class], @selector(myInitWithCoder:));
    method_exchangeImplementations(imp, myImp);
}

- (id)myInitWithCoder:(NSCoder*)aDecode{
    [self myInitWithCoder:aDecode];
    if (self) {
        //部分不像改变字体的 把tag值设置成333跳过
        if(self.tag != 333){
            CGFloat fontSize = self.font.pointSize;
            self.font = [UIFont systemFontOfSize:fontSize * SizeScale];
        }
    }
    return self;
}

@end

@implementation UITextField (myFont)

+ (void)load{
    Method imp = class_getInstanceMethod([self class], @selector(initWithCoder:));
    Method myImp = class_getInstanceMethod([self class], @selector(myInitWithCoder:));
    method_exchangeImplementations(imp, myImp);
}

- (id)myInitWithCoder:(NSCoder*)aDecode{
    [self myInitWithCoder:aDecode];
    if (self) {
        //部分不像改变字体的 把tag值设置成333跳过
        if(self.tag != 333){
            CGFloat fontSize = self.font.pointSize;
            self.font = [UIFont systemFontOfSize:fontSize * SizeScale];
        }
    }
    return self;
}

@end

@implementation UITextView (myFont)

+ (void)load{
    Method imp = class_getInstanceMethod([self class], @selector(initWithCoder:));
    Method myImp = class_getInstanceMethod([self class], @selector(myInitWithCoder:));
    method_exchangeImplementations(imp, myImp);
}

- (id)myInitWithCoder:(NSCoder*)aDecode{
    [self myInitWithCoder:aDecode];
    if (self) {
        //部分不像改变字体的 把tag值设置成333跳过
        if(self.tag != 333){
            CGFloat fontSize = self.font.pointSize;
            self.font = [UIFont systemFontOfSize:fontSize * SizeScale];
        }
    }
    return self;
}

@end