安卓设计模式之原型模式

最新推荐文章于 2022-12-21 10:56:29 发布

转载最新推荐文章于 2022-12-21 10:56:29 发布 · 319 阅读

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用原型实例指定创建对象的种类，并通过拷贝这些原型创建新的对象。

首先我们定义一个Person类

public class Person{
    private String name;
    private int age;
    private double height;
    private double weight;

    public Person(){
        
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    public double getWeight() {
        return weight;
    }

    public void setWeight(double weight) {
        this.weight = weight;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", height=" + height +
                ", weight=" + weight +
                '}';
    }
}

要实现原型模式，只需要按照下面的几个步骤去实现即可。

实现Cloneable接口

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public class Person implements Cloneable{

}

重写Object的clone方法

@Override
public Object clone(){
	return null;
}

实现clone方法中的拷贝逻辑

@Override
public Object clone(){
	Person person=null;
	try {
		person=(Person)super.clone();
		person.name=this.name;
		person.weight=this.weight;
		person.height=this.height;
		person.age=this.age;
	} catch (CloneNotSupportedException e) {
		e.printStackTrace();
	}
	return person;
}

测试一下

public class Main {
    public static void main(String [] args){
        Person p=new Person();
        p.setAge(18);
        p.setName("张三");
        p.setHeight(178);
        p.setWeight(65);
        System.out.println(p);

        Person p1= (Person) p.clone();
        System.out.println(p1);

        p1.setName("李四");
        System.out.println(p);
        System.out.println(p1);
    }
}

输出结果如下

Person{name=’张三’, age=18, height=178.0, weight=65.0}
Person{name=’张三’, age=18, height=178.0, weight=65.0}
Person{name=’张三’, age=18, height=178.0, weight=65.0}
Person{name=’李四’, age=18, height=178.0, weight=65.0}

试想一下，两个不同的人，除了姓名不一样，其他三个属性都一样，用原型模式进行拷贝就会显得异常简单，这也是原型模式的应用场景之一。

一个对象需要提供给其他对象访问，而且各个调用者可能都需要修改其值时，可以考虑使用原型模式拷贝多个对象供调用者使用，即保护性拷贝。

但是假设Person类里还有一个属性叫兴趣爱好，是一个List集合，就像这样子

private ArrayList<String> hobbies=new ArrayList<String>();

public ArrayList<String> getHobbies() {
	return hobbies;
}

public void setHobbies(ArrayList<String> hobbies) {
	this.hobbies = hobbies;
}

在进行拷贝的时候要格外注意，如果你直接按之前的代码那样拷贝

@Override
public Object clone(){
	Person person=null;
	try {
		person=(Person)super.clone();
		person.name=this.name;
		person.weight=this.weight;
		person.height=this.height;
		person.age=this.age;
		person.hobbies=this.hobbies;
	} catch (CloneNotSupportedException e) {
		e.printStackTrace();
	}
	return person;
}

会带来一个问题

使用测试代码进行测试

public class Main {
    public static void main(String [] args){
        Person p=new Person();
        p.setAge(18);
        p.setName("张三");
        p.setHeight(178);
        p.setWeight(65);
        ArrayList <String> hobbies=new ArrayList<String>();
        hobbies.add("篮球");
        hobbies.add("编程");
        hobbies.add("长跑");
        p.setHobbies(hobbies);
        System.out.println(p);

        Person p1= (Person) p.clone();
        System.out.println(p1);

        p1.setName("李四");
        p1.getHobbies().add("游泳");
        System.out.println(p);
        System.out.println(p1);
    }
}

我们拷贝了一个对象，并添加了一个兴趣爱好进去，看下打印结果

Person{name=’张三’, age=18, height=178.0, weight=65.0, hobbies=[篮球, 编程, 长跑]}
Person{name=’张三’, age=18, height=178.0, weight=65.0, hobbies=[篮球, 编程, 长跑]}
Person{name=’张三’, age=18, height=178.0, weight=65.0, hobbies=[篮球, 编程, 长跑, 游泳]}
Person{name=’李四’, age=18, height=178.0, weight=65.0, hobbies=[篮球, 编程, 长跑, 游泳]}

你会发现原来的对象的hobby也发生了变换。

其实导致这个问题的本质原因是我们只进行了浅拷贝，也就是只拷贝了引用，最终两个对象指向的引用是同一个，一个发生变化另一个也会发生变换，显然解决方法就是使用深拷贝。

@Override
public Object clone(){
	Person person=null;
	try {
		person=(Person)super.clone();
		person.name=this.name;
		person.weight=this.weight;
		person.height=this.height;
		person.age=this.age;

		person.hobbies=(ArrayList<String>)this.hobbies.clone();
	} catch (CloneNotSupportedException e) {
		e.printStackTrace();
	}
	return person;
}

注意person.hobbies=(ArrayList)this.hobbies.clone();，不再是直接引用而是进行了一份拷贝。再运行一下，就会发现原来的对象不会再发生变化了。

Person{name=’张三’, age=18, height=178.0, weight=65.0, hobbies=[篮球, 编程, 长跑]}
Person{name=’张三’, age=18, height=178.0, weight=65.0, hobbies=[篮球, 编程, 长跑]}
Person{name=’张三’, age=18, height=178.0, weight=65.0, hobbies=[篮球, 编程, 长跑]}
Person{name=’李四’, age=18, height=178.0, weight=65.0, hobbies=[篮球, 编程, 长跑, 游泳]}

其实有时候我们会更多的看到原型模式的另一种写法。

在clone函数里调用构造函数，构造函数的入参是该类对象。

@Override
public Object clone(){
	return new Person(this);
}

在构造函数中完成拷贝逻辑

public Person(Person person){
	this.name=person.name;
	this.weight=person.weight;
	this.height=person.height;
	this.age=person.age;
	this.hobbies= new ArrayList<String>(hobbies);
}

其实都差不多，只是写法不一样。

现在来挖挖android中的原型模式。

先看Bundle类，该类实现了Cloneable接口

public Object clone() {
	return new Bundle(this);
} 
public Bundle(Bundle b) {
	super(b);

	mHasFds = b.mHasFds;
	mFdsKnown = b.mFdsKnown;
}

然后是Intent类，该类也实现了Cloneable接口

@Override
public Object clone() {
	return new Intent(this);
}
public Intent(Intent o) {
	this.mAction = o.mAction;
	this.mData = o.mData;
	this.mType = o.mType;
	this.mPackage = o.mPackage;
	this.mComponent = o.mComponent;
	this.mFlags = o.mFlags;
	this.mContentUserHint = o.mContentUserHint;
	if (o.mCategories != null) {
		this.mCategories = new ArraySet<String>(o.mCategories);
	}
	if (o.mExtras != null) {
		this.mExtras = new Bundle(o.mExtras);
	}
	if (o.mSourceBounds != null) {
		this.mSourceBounds = new Rect(o.mSourceBounds);
	}
	if (o.mSelector != null) {
		this.mSelector = new Intent(o.mSelector);
	}
	if (o.mClipData != null) {
		this.mClipData = new ClipData(o.mClipData);
	}
}

用法也显得十分简单，一旦我们要用的Intent与现有的一个Intent很多东西都是一样的，那我们就可以直接拷贝现有的Intent，再修改不同的地方，便可以直接使用。

Uri uri = Uri.parse("smsto:10086");    
Intent shareIntent = new Intent(Intent.ACTION_SENDTO, uri);    
shareIntent.putExtra("sms_body", "hello");    

Intent intent = (Intent)shareIntent.clone() ;
startActivity(intent);

网络请求中一个最常见的开源库OkHttp中，也应用了原型模式。它就在OkHttpClient这个类中，它实现了Cloneable接口

/** Returns a shallow copy of this OkHttpClient. */
@Override 
public OkHttpClient clone() {
	return new OkHttpClient(this);
}
private OkHttpClient(OkHttpClient okHttpClient) {
	this.routeDatabase = okHttpClient.routeDatabase;
	this.dispatcher = okHttpClient.dispatcher;
	this.proxy = okHttpClient.proxy;
	this.protocols = okHttpClient.protocols;
	this.connectionSpecs = okHttpClient.connectionSpecs;
	this.interceptors.addAll(okHttpClient.interceptors);
	this.networkInterceptors.addAll(okHttpClient.networkInterceptors);
	this.proxySelector = okHttpClient.proxySelector;
	this.cookieHandler = okHttpClient.cookieHandler;
	this.cache = okHttpClient.cache;
	this.internalCache = cache != null ? cache.internalCache : okHttpClient.internalCache;
	this.socketFactory = okHttpClient.socketFactory;
	this.sslSocketFactory = okHttpClient.sslSocketFactory;
	this.hostnameVerifier = okHttpClient.hostnameVerifier;
	this.certificatePinner = okHttpClient.certificatePinner;
	this.authenticator = okHttpClient.authenticator;
	this.connectionPool = okHttpClient.connectionPool;
	this.network = okHttpClient.network;
	this.followSslRedirects = okHttpClient.followSslRedirects;
	this.followRedirects = okHttpClient.followRedirects;
	this.retryOnConnectionFailure = okHttpClient.retryOnConnectionFailure;
	this.connectTimeout = okHttpClient.connectTimeout;
	this.readTimeout = okHttpClient.readTimeout;
	this.writeTimeout = okHttpClient.writeTimeout;
}