26.怎样在Swift中定义宏？

　　Swift 中没有宏定义，苹果建议使用let 或者 get 属性来替代宏定义值。虽然没有#define，但我们仍然可以使用 #if 并配合编译的配置来完成条件编译。下面会列出Swift项目开发中的一些常用宏定义，并提供源码。

1.常用字体宏定义

import Foundation
import UIKit

/// 系统普通字体
var gof_SystemFontWithSize: (CGFloat) -> UIFont = {size in
    return UIFont.systemFontOfSize(size);
}

/// 系统加粗字体
var gof_BoldFontWithSize: (CGFloat) -> UIFont = {size in
    return UIFont.boldSystemFontOfSize(size);
}

/// 仅用于标题栏上，大标题字号
let kNavFont = gof_SystemFontWithSize(18);

/// 标题字号
let kTitleFont = gof_SystemFontWithSize(18);

/// 正文字号
let kBodyFont = gof_SystemFontWithSize(16);

/// 辅助字号
let kAssistFont = gof_SystemFontWithSize(14);

2.常用颜色宏定义

import Foundation
import UIKit

/// 根据RGBA生成颜色(格式为：22,22,22,0.5)
var gof_RGBAColor: (CGFloat, CGFloat, CGFloat, CGFloat) -> UIColor = {red, green, blue, alpha in
    return UIColor(red: red / 255, green: green / 255, blue: blue / 255, alpha: alpha);
}

/// 根据RGB生成颜色(格式为：22,22,22)
var gof_RGBColor: (CGFloat, CGFloat, CGFloat) -> UIColor = {red, green, blue in
    return UIColor(red: red / 255, green: green / 255, blue: blue / 255, alpha: 1);
}

/// 根据色值生成颜色(无透明度)(格式为0xffffff)
var gof_ColorWithHex: (NSInteger) -> UIColor = {hex in
    return UIColor(red: ((CGFloat)((hex & 0xFF0000) >> 16)) / 255.0, green: ((CGFloat)((hex & 0xFF00) >> 8)) / 255.0, blue: ((CGFloat)(hex & 0xFF)) / 255.0, alpha: 1);
}

/// 黑色
let kBColor = gof_ColorWithHex(0x000000);
/// 白色
let kWColor = gof_ColorWithHex(0xffffff)
/// 无色
let kCColor = UIColor.clearColor();
let kG1Color = gof_ColorWithHex(0x323232);
let kG2Color = gof_ColorWithHex(0x646464);
let kG3Color = gof_ColorWithHex(0x969696);
let kG4Color = gof_ColorWithHex(0xc8c8c8); // 仅使用标题栏分割线
let kG5Color = gof_ColorWithHex(0xdcdcdc); // 主页面分割线
let kG6Color = gof_ColorWithHex(0xf0f0f0); // 仅用于背景灰
let kBgColor  = gof_ColorWithHex(0xf8f8f8); // 界面背景颜色
let kHolderTipColor = gof_ColorWithHex(0xafafaf); // 提示：输入框，这个提示语的颜色
let kButtonBlueColor = gof_ColorWithHex(0x41acff);

let kLightColor = gof_ColorWithHex(0x666666);
let kGrayTitleColor = gof_ColorWithHex(0x999999);
let kGrayTipColor = gof_ColorWithHex(0x757575);

let k323232Color = gof_ColorWithHex(0x323232);
let k646464Color = gof_ColorWithHex(0x646464);
let k969696Color = gof_ColorWithHex(0x969696);
let kf0f0f0Color = gof_ColorWithHex(0xf0f0f0);

/// 三大色调
let kEssentialColor = gof_ColorWithHex(0x46a0f0);  // 主色调，蓝色
let kAssistOrangeColor = gof_ColorWithHex(0xff8c28);  // 辅色调，橙色
let kAssistGreenColor = gof_ColorWithHex(0x5abe00);  // 辅色调，绿色

3.常用变量/方法定义

import Foundation
import UIKit

// MARK: - 打印日志

/**
 打印日志
 
 - parameter message: 日志消息内容
 */
func printLog<T>(message: T)
{
    #if DEBUG
        print(" (message)");
    #endif
}

// MARK: - 线程队列

/// 主线程队列
let kMainThread = dispatch_get_main_queue();
/// Global队列
let kGlobalThread = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

// MARK: - 系统版本

/// 获取系统版本号
let kSystemVersion = Float(UIDevice.currentDevice().systemVersion);
/// 是否IOS7系统
let kIsIOS7OrLater = Int(UIDevice.currentDevice().systemVersion) >= 7 ? true : false;
/// 是否IOS8系统
let kIsIOS8OrLater = Int(UIDevice.currentDevice().systemVersion) >= 8 ? true : false;
/// 是否IOS9系统
let kIsIOS9OrLater = Int(UIDevice.currentDevice().systemVersion) >= 9 ? true : false;

// MARK: - 常用宽高

/// 屏幕Bounds
let kScreenBounds = UIScreen.mainScreen().bounds;
/// 屏幕高度
let kScreenHeight = UIScreen.mainScreen().bounds.size.height;
/// 屏幕宽度
let kScreenWidth = UIScreen.mainScreen().bounds.size.width;
/// 导航栏高度
let kNavBarHeight = 44.0;
/// 状态栏高度
let kStatusBarHeight = 20.0;
/// Tab栏高度
let kTabBarHeight = 49.0;

//根据图片名称获取图片
let gof_ImageWithName: (String) -> UIImage? = {imageName in
    return UIImage(named: imageName);
}

　　【注意】：上面的printLog用了条件编译，DEBUG需要在TARGET中配置一下，具体如下图：