Hybrid App: 了解原生JavaScriptCore框架是如何让JavaScript与Native实现混合开发

一、简介

Hybrid Development混合开发是目前移动端开发异常火热的新兴技术，它能够实现跨平台开发，极大地节约了人力和资源成本。跨平台开发催生了很多新的开源框架，就目前而言，在混合开发中比较流行的有FaceBook开源React Native，有Goggle开源的Flutter。React Native实现的是通过下发JS脚本的方式达到JS与Native交互。Flutter实现的则是通过采用现代响应式框架来构建UI，Flutter与ReactiveCocoa框架配合使用最佳。当然开发者也可以在Native中内嵌WebView的方式(WebKit)实现混合开发。虽然方式不同，但目的相同，都是跨平台，殊途同归吧。对跨平台有了粗略的了解后，再来看看iOS系统中对JS与Native是如何交互的，其实，系统是给开发者提供了一个极其强大的框架来实现这个功能的，即JavaScriptCore框架。这个框架通过定义JSValue值对象和声明JSExport协议作为桥梁完成Native与JS的通信。JS虽然是单线程语言，但是iOS是支持多线程执行任务的，开发者可以在异步情况下执行任意一个环境的JavaScript代码。大概结构图如下：

 

二、分析

参考这上图，可以看出JavaScriptCore框架结构还是很清晰的，JavaScriptCore中有那么几个核心的类在开发者是很常用的，需要弄懂它们代表的意思。

  

 

三、API

知道了这几个核心类的概念已经对这个框架有了个基本的认识，具体的API如何使用，我们可以选择性点击去深入研究一下。只有对它们的属性和方法都了如指掌，开发起来才能得心应手，手到擒来。哎呀妈，不废话了。。。例如JSContext和JSValue开发中必用的类，额外的可能还会用JSManagerValue，如下：

JSContetxt类：

//初始化，可以选择对应的虚拟机
- (instancetype)init;
- (instancetype)initWithVirtualMachine:(JSVirtualMachine *)virtualMachine;

//执行js代码，返回js值对象
- (JSValue *)evaluateScript:(NSString *)script;
- (JSValue *)evaluateScript:(NSString *)script withSourceURL:(NSURL *)sourceURL;

//获取当前的js上下文
+ (JSContext *)currentContext;

//获取当前的js执行函数，返回js值对象
+ (JSValue *)currentCallee;

//获取当前的js函数中this指向的对象，返回js值对象
+ (JSValue *)currentThis;

//获取当前的js函数中的所有参数
+ (NSArray *)currentArguments;

//js的全局对象
@property (readonly, strong) JSValue *globalObject;

//js执行的异常数据
@property (strong) JSValue *exception;
@property (copy) void(^exceptionHandler)(JSContext *context, JSValue *exception);

//js运行的虚拟机
@property (readonly, strong) JSVirtualMachine *virtualMachine;

//js上下文名称
@property (copy) NSString *name;

//分类
@interface JSContext (SubscriptSupport)
//获取和设置属性为js全局对象
- (JSValue *)objectForKeyedSubscript:(id)key;
- (void)setObject:(id)object forKeyedSubscript:(NSObject <NSCopying> *)key;
@end

//分类（C函数风格）
@interface JSContext (JSContextRefSupport)
//获取和设置全局上下文
+ (JSContext *)contextWithJSGlobalContextRef:(JSGlobalContextRef)jsGlobalContextRef;
@property (readonly) JSGlobalContextRef JSGlobalContextRef;
@end

JSValue类：

//js上下文
@property (readonly, strong) JSContext *context;

//使用OC数据初始化js值对象，创建有值的JSValue
+ (JSValue *)valueWithObject:(id)value inContext:(JSContext *)context;
+ (JSValue *)valueWithBool:(BOOL)value inContext:(JSContext *)context;
+ (JSValue *)valueWithDouble:(double)value inContext:(JSContext *)context;
+ (JSValue *)valueWithInt32:(int32_t)value inContext:(JSContext *)context;
+ (JSValue *)valueWithUInt32:(uint32_t)value inContext:(JSContext *)context;
+ (JSValue *)valueWithPoint:(CGPoint)point inContext:(JSContext *)context;
+ (JSValue *)valueWithRange:(NSRange)range inContext:(JSContext *)context;
+ (JSValue *)valueWithRect:(CGRect)rect inContext:(JSContext *)context;
+ (JSValue *)valueWithSize:(CGSize)size inContext:(JSContext *)context;

//使用OC数据初始化js值对象，创建空的JSValue
+ (JSValue *)valueWithNewObjectInContext:(JSContext *)context;
+ (JSValue *)valueWithNewArrayInContext:(JSContext *)context;
+ (JSValue *)valueWithNewRegularExpressionFromPattern:(NSString *)pattern flags:(NSString *)flags inContext:(JSContext *)context;
+ (JSValue *)valueWithNewErrorFromMessage:(NSString *)message inContext:(JSContext *)context;
+ (JSValue *)valueWithNewPromiseInContext:(JSContext *)context fromExecutor:(void (^)(JSValue *resolve, JSValue *reject))callback;
+ (JSValue *)valueWithNewPromiseResolvedWithResult:(id)result inContext:(JSContext *)context;
+ (JSValue *)valueWithNewPromiseRejectedWithReason:(id)reason inContext:(JSContext *)context;
+ (JSValue *)valueWithNewSymbolFromDescription:(NSString *)description inContext:(JSContext *)context;
+ (JSValue *)valueWithNullInContext:(JSContext *)context;
+ (JSValue *)valueWithUndefinedInContext:(JSContext *)context;

//js数据转OC数据
- (id)toObject;
- (id)toObjectOfClass:(Class)expectedClass;
- (BOOL)toBool;
- (double)toDouble;
- (int32_t)toInt32;
- (uint32_t)toUInt32;
- (NSNumber *)toNumber;
- (NSString *)toString;
- (NSDate *)toDate;
- (NSArray *)toArray;
- (NSDictionary *)toDictionary;
- (CGPoint)toPoint;
- (NSRange)toRange;
- (CGRect)toRect;
- (CGSize)toSize;

//js值对象判断
@property (readonly) BOOL isUndefined;
@property (readonly) BOOL isNull;
@property (readonly) BOOL isBoolean;
@property (readonly) BOOL isNumber;
@property (readonly) BOOL isString;
@property (readonly) BOOL isObject;
@property (readonly) BOOL isArray; 
@property (readonly) BOOL isDate;
@property (readonly) BOOL isSymbol;
- (BOOL)isEqualToObject:(id)value;
- (BOOL)isEqualWithTypeCoercionToObject:(id)value;
- (BOOL)isInstanceOf:(id)value;

//js调用函数
- (JSValue *)callWithArguments:(NSArray *)arguments;
- (JSValue *)constructWithArguments:(NSArray *)arguments;
- (JSValue *)invokeMethod:(NSString *)method withArguments:(NSArray *)arguments;

//js属性设置
- (JSValue *)valueForProperty:(JSValueProperty)property;
- (void)setValue:(id)value forProperty:(JSValueProperty)property;
- (BOOL)deleteProperty:(JSValueProperty)property;
- (BOOL)hasProperty:(JSValueProperty)property;
- (void)defineProperty:(JSValueProperty)property descriptor:(id)descriptor;
- (JSValue *)valueAtIndex:(NSUInteger)index;
- (void)setValue:(id)value atIndex:(NSUInteger)index;
- (JSValue *)objectForKeyedSubscript:(id)key;
- (JSValue *)objectAtIndexedSubscript:(NSUInteger)index;
- (void)setObject:(id)object forKeyedSubscript:(id)key;
- (void)setObject:(id)object atIndexedSubscript:(NSUInteger)index;
+ (JSValue *)valueWithJSValueRef:(JSValueRef)value inContext:(JSContext *)context;

//OC与JS类型对应关系
  Objective-C type    |   JavaScript type
 ---------------------+---------------------
         nil          |     undefined
        NSNull        |        null
       NSString       |       string
       NSNumber       |   number, boolean
     NSDictionary     |   Object object
       NSArray        |    Array object
        NSDate        |     Date object
       NSBlock (1)    |   Function object (1)
          id (2)      |   Wrapper object (2)
        Class (3)     | Constructor object (3)
 ---------------------+---------------------

JSManagerValue类：

//对JSValue进行一层包装，对内存进行有效的管理，防止提前或者过度释放
+ (JSManagedValue *)managedValueWithValue:(JSValue *)value;
+ (JSManagedValue *)managedValueWithValue:(JSValue *)value andOwner:
- (instancetype)initWithValue:(JSValue *)value;
@property (readonly, strong) JSValue *value;

 

四、案例

[1] 首先打开Safari浏览器的web检查器，会用来查看js运行的效果 ，控制台打印

[2] 导入JavaScriptCore框架

[3] 导入头文件开始测试，Native调用JS

[3-1] 调用无参数的JS函数

native.js

-(void)nativeCallJs {
    
    //方式一
    //从js文件获取js代码
    NSString *path = [[NSBundle mainBundle] pathForResource:@"native" ofType:@"js"];
    NSData *jsData = [NSData dataWithContentsOfFile:path];
    NSString *script = [[NSString alloc] initWithData:jsData encoding:NSUTF8StringEncoding];
    
    //执行js代码
    [self.jsContext evaluateScript:script];
}

-(void)nativeCallJs {
    
    //方式二
    //js代码写在端上
    NSString *script = @"\
                    (function(){ \
                        console.log(\"native call js ------- Wellcome Native\");\
                    })();";
  
    //执行js代码
    [self.jsContext evaluateScript:script];
}

- (void)viewDidLoad {
    [super viewDidLoad];

    //js上下文
    self.jsContext = [[JSContext alloc] init];
    
    //native调用js
    [self nativeCallJs];
}

[3-2] 调用有参数的JS函数

native.js

-(void)nativeCallJsWithArguments:(NSString *)argument {
    
    //方式一
    //从js文件获取js代码
    NSString *path = [[NSBundle mainBundle] pathForResource:@"native" ofType:@"js"];
    NSData *jsData = [NSData dataWithContentsOfFile:path];
    NSString *jsString = [[NSString alloc] initWithData:jsData encoding:NSUTF8StringEncoding];
    
    //拼接js参数
    NSString *script = [NSString stringWithFormat:jsString,argument];
    
    //执行js代码
    [self.jsContext evaluateScript:script];
}

-(void)nativeCallJsWithArguments:(NSString *)argument {
    
    //方式二
    //js代码写在端上
    NSString *jsString = @"\
                    function receive(argument) { \
                        console.log(\"native call js ------- Wellcome \"+argument);\
                    };\
                    receive('%@')";
    
    //拼接js参数
    NSString *script = [NSString stringWithFormat:jsString,argument];
    
    //执行js代码
    [self.jsContext evaluateScript:script];
}

- (void)viewDidLoad {
    [super viewDidLoad];
    
    //js上下文
    self.jsContext = [[JSContext alloc] init];
    
    //native调用js
    [self nativeCallJsWithArguments:@"我的老哥"];
}

[4] 导入头文件开始测试，JS调用Native

注意：调用包括无参数和有参数的OC方法，这里使用代码块Block为例

-(void)jsCallNative {
    
    //定义无参数block
    void (^Block1)(void) = ^(){
        NSLog(@"js call native ------- hello JavaScript");
    };
    
    //定义有参数block
    void (^Block2)(NSString *) = ^(NSString *argument){
        NSLog(@"js call native ------- hello JavaScript----Wellcome %@",argument);
    };
    
    //设置block为JSContext全局对象的属性，然后可以在safari控制台执行函数oc_block()输出打印;
    [self.jsContext setObject:Block1 forKeyedSubscript:@"oc_block1"];
    [self.jsContext setObject:Block2 forKeyedSubscript:@"oc_block2"];
}

- (void)viewDidLoad {
    [super viewDidLoad];
    
    //js上下文
    self.jsContext = [[JSContext alloc] init];

    //js调用native
    [self jsCallNative];
}

[5]导入头文件开始测试， OC和JS对象的映射

//OC与JS数据传递的数据就是JSValue值对象，存储在JS的全局对象中
//存和取的过程
[self.jsContext setObject:(id) forKeyedSubscript:(NSObject<NSCopying> *)];
[self.jsContext objectForKeyedSubscript:(id)]

[5-1] 系统提供的OC数据类型，不用特殊存储，可以直接存取

//系统提供的OC数据类型，不用特殊存储，可以直接存取
[self.jsContext setObject:@"mac" forKeyedSubscript:@"os"];
JSValue *osValue = [self.jsContext objectForKeyedSubscript:@"os"];
NSString *osName = [osValue toString];
NSLog(@"-----osName = %@-----",osName);

2019-11-12 14:58:17.471840+0800 混合开发[10499:365654] -----osName = mac-----

[5-2] 特殊的OC类型，如自定义对象，则必须遵守JSExport协议，JS才能拿到自定义对象的所有属性和方法

#import <UIKit/UIKit.h>
#import <JavaScriptCore/JavaScriptCore.h>

//遵守JSExport协议，使得JS在上下文中可以获取到OC中定义的属性和方法
@protocol PersonProtocol <JSExport>
@property (nonatomic,   copy) NSString *name;
@property (nonatomic, assign) int age;
@property (nonatomic, assign) int grade;
@property (nonatomic, assign) float score;
-(void)description;
@end

@interface Person : NSObject<PersonProtocol>
@property (nonatomic,   copy) NSString *name;
@property (nonatomic, assign) int age;
@property (nonatomic, assign) int grade;
@property (nonatomic, assign) float score;
-(void)description;
@end

#import "Person.h"
@implementation Person
-(void)description {
    NSLog(@"姓名：name = %@",self.name);
    NSLog(@"年龄：age = %d",self.age);
    NSLog(@"年级：grade = %d",self.grade);
    NSLog(@"分数：score = %.1f",self.score);
}
@end

//特殊的OC类型，自定义对象，则必须遵守JSExport协议，JS才能拿到自定义对象的所有属性和方法
Person *person = [[Person alloc] init];
person.name = @"张三";
person.age = 20;
person.grade = 5;
person.score = 98;
[self.jsContext setObject:person forKeyedSubscript:@"personEntity"];
JSValue *personValue = [self.jsContext objectForKeyedSubscript:@"personEntity"]; //personEntity为OC在JS的对象形式
Person *xyq_person = (Person *)[personValue toObject];
[xyq_person description];

2019-11-12 14:58:17.472563+0800 混合开发[10499:365654] 姓名：name = 张三
2019-11-12 14:58:17.472709+0800 混合开发[10499:365654] 年龄：age = 20
2019-11-12 14:58:17.472810+0800 混合开发[10499:365654] 年级：grade = 5
2019-11-12 14:58:17.472889+0800 混合开发[10499:365654] 分数：score = 98.0

 

五、实践

到现在为止，相信我们对JS和Native的交互原理有了自己的理解。在案例中使用了js文件下发和解析的方式实现了Native执行JS代码，这个正是Facebook开源的React Native的设计思路。React Native支持跨平台，通过一套js文件就可以在Andriod和iOS上完成Native的界面渲染。现在我们通过一个小测试来模拟Hybrid App的构建原理，通过按钮点击切换控制器视图的背景色。

(1) 创建JavaScript脚本，在脚本中创建Native需要的任意UI控件存到数组，作为函数的返回值

UIKit.js

//定义一个自调用函数，JavaScript脚本加载完成立即执行
(function(){
    return renderUI();
 })();

/* JavaScript脚本  定义一个Label类
 * rect：尺寸   text：文本  color：颜色
 */
function Label(rect,text,fontSize,textColor,textAlignment,bgColor){
    this.rect = rect;
    this.text = text;
    this.fontSize = fontSize;
    this.textColor = textColor;
    this.textAlignment = textAlignment; //NSTextAlignmentCenter = 1
    this.bgColor = bgColor;
    this.type = "Label";
}

/* JavaScript脚本  定义一个Button类
 * rect：尺寸   text：文本  color：颜色  callFunction：函数
 */
function Button(rect,title,fontSize,titleColor,bgColor,callFunction){
    this.rect = rect;
    this.title = title;
    this.fontSize = fontSize;
    this.titleColor = titleColor;
    this.bgColor = bgColor;
    this.callFunction = callFunction;
    this.type = "Button";
}

/* JavaScript脚本  Rect类
 * x：坐标x   y：坐标y  w：宽度  h：高度
 */
function Rect(x,y,w,h){
    this.x = x;
    this.y = y;
    this.w = w;
    this.h = h;
}

/* JavaScript脚本  Color类
 * r：red  g：green  b：black  a：alpa
 */
function Color(r,g,b,a){
    this.r = r;
    this.g = g;
    this.b = b;
    this.a = a;
}

//渲染方法，实例化上面类的对象
function renderUI() {
    
    //创建js标签对象
    var screenWidth = 375.0;
    var labeWidth = 200;
    var labelRect = new Rect((screenWidth-labeWidth)*0.5, 100, labeWidth, 44);
    var labeFontSize  = 20;
    var labelTextColor = new Color(1,0,0,1);
    var labelBgColor = new Color(1,1,0,1);
    var label = new Label(labelRect, "I From JS", labeFontSize, labelTextColor, 1, labelBgColor);
    
    //创建js按钮对象
    var buttonWidth = 200;
    var buttonRect = new Rect((screenWidth-buttonWidth)*0.5, 200, buttonWidth, buttonWidth);
    var buttonFontSize  = 40;
    var buttonTitleColor = new Color(1,0,1,1);
    var buttonbgColor = new Color(1,1,1,1);
    var button = new Button(buttonRect,"Button",buttonFontSize,buttonTitleColor,buttonbgColor,function(r,g,b){
                                var randColor = new Color(r,g,b,1);
                                configEntity.chageViewColor(randColor);
                          });
    
    //返回js对象
    return [label, button];
    
}

(2) 创建自定义对象，遵守JSExport协议，添加为JS的全局对象的属性，作为与Native交互的桥接器

//自定义Config类
#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
#import <JavaScriptCore/JavaScriptCore.h>

NS_ASSUME_NONNULL_BEGIN

@protocol ConfigProtocol <JSExport>
-(void)chageViewColor:(JSValue *)colorValue;
@end

@interface Config : NSObject<ConfigProtocol>
@property (nonatomic, strong) UIViewController *currentVc;
-(void)chageViewColor:(JSValue *)colorValue; //改变当前控制器视图背景色
@end

NS_ASSUME_NONNULL_END

//Created by 夏远全 on 2019/11/12.

#import "Config.h"

@implementation Config

-(void)chageViewColor:(JSValue *)colorValue {
    
    CGFloat red = colorValue[@"r"].toDouble;
    CGFloat green = colorValue[@"g"].toDouble;
    CGFloat blue = colorValue[@"b"].toDouble;
    CGFloat alpha = colorValue[@"a"].toDouble;

    self.currentVc.view.backgroundColor = [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
}
@end

(3) 在VC中解析JavaScript脚本，获取UI控件元素，进行界面的渲染

#import "ViewController.h"
#import <JavaScriptCore/JavaScriptCore.h>
#import "Person.h"
#import "Config.h"

@interface ViewController ()
@property (nonatomic, strong) JSContext *jsContext;
@property (nonatomic, strong) NSMutableArray *actions; //所有的回调函数
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor redColor];
    
    //js上下文
    self.jsContext = [[JSContext alloc] init];
    
    //从JS文件获取UI进行渲染
    [self renderUIFromJs];
}

-(void)renderUIFromJs {
    
    //创建Config对象
    Config *config = [[Config alloc] init];
    config.currentVc = self;
    [self.jsContext setObject:config forKeyedSubscript:@"configEntity"];
    
    //从js文件获取js代码
    NSString *path = [[NSBundle mainBundle] pathForResource:@"UIKit" ofType:@"js"];
    NSData *jsData = [NSData dataWithContentsOfFile:path];
    NSString *script = [[NSString alloc] initWithData:jsData encoding:NSUTF8StringEncoding];
    
    //执行js代码
    JSValue *jsValue = [self.jsContext evaluateScript:script];
    for (int i=0; i<jsValue.toArray.count; i++) {
        
        //取出每一个控件对象值
        JSValue *subValue = [jsValue objectAtIndexedSubscript:i];
        
        //创建控件
        NSString *type = [subValue objectForKeyedSubscript:@"type"].toString;
        if ([type isEqualToString:@"Label"]) {
            
            //this.rect = rect;
            //this.text = text;
            //this.fontSize = fontSize;
            //this.textColor = textColor;
            //this.textAlignment = textAlignment; //NSTextAlignmentCenter = 1
            //this.bgColor = bgColor;
            //this.type = "Label";
            
            CGFloat X = subValue[@"rect"][@"x"].toDouble;
            CGFloat Y = subValue[@"rect"][@"y"].toDouble;
            CGFloat W = subValue[@"rect"][@"w"].toDouble;
            CGFloat H = subValue[@"rect"][@"h"].toDouble;
            NSString *text = subValue[@"text"].toString;
            NSInteger fontSize = subValue[@"fontSize"].toInt32;
            UIColor *textColor = [UIColor colorWithRed:subValue[@"textColor"][@"r"].toDouble green:subValue[@"textColor"][@"g"].toDouble blue:subValue[@"textColor"][@"b"].toDouble alpha:subValue[@"textColor"][@"a"].toDouble];
            UIColor *bgColor = [UIColor colorWithRed:subValue[@"bgColor"][@"r"].toDouble green:subValue[@"bgColor"][@"g"].toDouble blue:subValue[@"bgColor"][@"b"].toDouble alpha:subValue[@"bgColor"][@"a"].toDouble];
            NSTextAlignment alignment = subValue[@"textAlignment"].toInt32;
            
            UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(X, Y, W, H)];
            label.text = text;
            label.font = [UIFont systemFontOfSize:fontSize];
            label.textColor = textColor;
            label.textAlignment = alignment;
            label.backgroundColor = bgColor;
            [self.view addSubview:label];
            
        }
        if ([type isEqualToString:@"Button"]) {
            
            //this.rect = rect;
            //this.title = title;
            //this.fontSize = fontSize;
            //this.titleColor = titleColor;
            //this.bgColor = bgColor;
            //this.type = "Button";
            //this.callFunction = callFunction;
                
            CGFloat X = subValue[@"rect"][@"x"].toDouble;
            CGFloat Y = subValue[@"rect"][@"y"].toDouble;
            CGFloat W = subValue[@"rect"][@"w"].toDouble;
            CGFloat H = subValue[@"rect"][@"h"].toDouble;
            NSInteger fontSize = subValue[@"fontSize"].toInt32;
            NSString *title = subValue[@"title"].toString;
            UIColor *titleColor = [UIColor colorWithRed:subValue[@"titleColor"][@"r"].toDouble green:subValue[@"titleColor"][@"g"].toDouble blue:subValue[@"titleColor"][@"b"].toDouble alpha:subValue[@"titleColor"][@"a"].toDouble];
            UIColor *bgColor = [UIColor colorWithRed:subValue[@"bgColor"][@"r"].toDouble green:subValue[@"bgColor"][@"g"].toDouble blue:subValue[@"bgColor"][@"b"].toDouble alpha:subValue[@"bgColor"][@"a"].toDouble];
            
            JSValue *actionValue = subValue[@"callFunction"];
            [self.actions addObject:actionValue];
            
            UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(X, Y, W, H)];
            [button setTitleColor:titleColor forState:UIControlStateNormal];
            [button addTarget:self action:@selector(buttonClick:) forControlEvents:UIControlEventTouchUpInside];
            [button setTitle:title forState:UIControlStateNormal];
            button.titleLabel.font = [UIFont systemFontOfSize:fontSize];
            button.backgroundColor = bgColor;
            button.tag = self.actions.count-1;
            [self.view addSubview:button];
        }
    }
}

-(void)buttonClick:(UIButton *)button {
    
    JSValue *actionValue = [self.actions objectAtIndex:button.tag];
    [actionValue callWithArguments:@[@(arc4random_uniform(2)),@(arc4random_uniform(2)),@(arc4random_uniform(2))]];
    
}

- (NSMutableArray *)actions {
    if (!_actions) {
        _actions = [NSMutableArray array];
    }
    return _actions;
}

(4) 演示gif

 

六、思考

这个js文件目前是写死的放在了Bundle目录下，试想一下，如果在本地每次更改js文件后再重新渲染界面，是不是都得端上重新发版，例如样式相同改一个颜色啥的，发个版就太繁琐了。最好的做法是将js文件部署到服务器上，每次只需要更新js内容后提交到服务器，端上进入当前页面时，从服务器拉取新的js文件渲染界面即可，效率高，成本低，可以实现快速更新迭代。好开心，吃个竹子吧，😆