<<Effective OC>>读书笔记 --- 第十二条 理解消息转发

本文通过足球比赛中的传球比喻,介绍了Objective-C中的消息转发机制,包括resolveInstanceMethod、resolveClassMethod、forwardingTargetForSelector等方法,并探讨了如何利用这些机制实现外观模式,降低类之间的耦合度。

转自:http://www.cocoachina.com/ios/20151208/14595.html

这里写图片描述

打个比方:比赛足球时,脚下有球的那名球员,如果他的位置不利于射门或者他的球即将被对方球员抢断,这时最好是把球传出去,这里的球就相当于消息。

方案一:
+ (BOOL)resolveInstanceMethod:(SEL)sel
+ (BOOL)resolveClassMethod:(SEL)sel

方案二:
- (id)forwardingTargetForSelector:(SEL)aSelector

方案三:
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector;
- (void)forwardInvocation:(NSInvocation *)anInvocation;

这里体现一种设计模式
外观模式(Facade)

外观模式是为了解决类与类之家的依赖关系的,像spring一样,可以将类和类之间的关系配置到配置文件中,而外观模式就是将他们的关系放在一个Facade类中,降低了类类之间的耦合度,该模式中没有涉及到接口,看下类
这里写图片描述

我们可以利用消息转发,由一个外观类接受所有的消息,转发给不同的类处理。

<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <!-- Spring Boot 启动父依赖 --> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.2.0.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.zjh.student_mis</groupId> <artifactId>student_mis</artifactId> <version>0.0.1-SNAPSHOT</version> <name>student_mis</name> <description>Demo project for Spring Boot</description> <properties> <mybatis-spring-boot>1.2.0</mybatis-spring-boot> <mysql-connector>5.1.39</mysql-connector> <java.version>1.8</java.version> <repositories> <repository> <id>alimaven</id> <url>https://maven.aliyun.com/repository/public</url> </repository> </repositories> <pluginRepositories> <pluginRepository> <id>alimaven</id> <url>https://maven.aliyun.com/repository/public</url> </pluginRepository> </pluginRepositories> </properties> <dependencies> <!-- 阿里fastjson包JSON转换--> <dependency> <groupId>com.alibaba</groupId> <artifactId>fastjson</artifactId> <version>1.2.62</version> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter</artifactId> </dependency> <!-- Spring Boot Web 依赖 --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <!-- MySQL 连接驱动依赖 --> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.47</version> </dependency> <dependency> <groupId>com.mchange</groupId> <artifactId>c3p0</artifactId> <version>0.9.5.2</version> </dependency> <dependency> <groupId>com.alibaba</groupId> <artifactId>druid</artifactId> <version>RELEASE</version> </dependency> <!-- 分页插件 --> <dependency> <groupId>com.github.pagehelper</groupId> <artifactId>pagehelper-spring-boot-starter</artifactId> <version>1.2.3</version> </dependency> <!-- Spring Boot Mybatis 依赖 --> <dependency> <groupId>org.mybatis.spring.boot</groupId> <artifactId>mybatis-spring-boot-starter</artifactId> <version>1.3.1</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-thymeleaf</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> <exclusions> <exclusion> <groupId>org.junit.vintage</groupId> <artifactId>junit-vintage-engine</artifactId> </exclusion> </exclusions> </dependency> <!-- Junit --> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> </dependency> <!--token--> <dependency> <groupId>com.auth0</groupId> <artifactId>java-jwt</artifactId> <version>3.4.0</version> </dependency> <!-- <dependency>--> <!-- <groupId>org.testng</groupId>--> <!-- <artifactId>testng</artifactId>--> <!-- <version>RELEASE</version>--> <!-- <scope>compile</scope>--> <!-- </dependency>--> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> <plugin> <groupId>org.mybatis.generator</groupId> <artifactId>mybatis-generator-maven-plugin</artifactId> <version>1.3.2</version> <configuration> <configurationFile>GeneratorMapper.xml</configurationFile> <verbose>true</verbose> <overwrite>true</overwrite> </configuration> </plugin> </plugins> <resources> <resource> <directory>src/main/java</directory> <includes> <include>**/*.xml</include> </includes> </resource> <resource> <directory>src/main/resources</directory> <includes> <include>**/*.*</include> </includes> </resource> <resource> <directory>src/main/webapp</directory> <targetPath>META-INF/resources</targetPath> <includes> <include>**/*.*</include> </includes> </resource> </resources> </build> </project> 这是pom.xml 解决上述问题
05-28
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