android常用的设计模式总结 一

前言

对于开发人员来说,设计模式是提高编程水平的一个非常重要的门槛.
以前写过一些设计模式的文章,有兴趣可以参考一下.
这一次来写一下android中设计模式的应用,相信你会对设计模式有一个更深入的理解.
什么是设计模式？
设计模式大总结-创建型模式
设计模式大总结2-结构型模式

单例模式

public class Singleton {
    private static Singleton instance;
    public static Singleton getInstace(){
        if (instance==null){
            synchronized (Singleton.class){
                if (instance==null) {
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }
}

• 使用synchronized 进行同步处理，并且双重判断是否为null，是因为如果有多个线程同时访问，这时候前一个线程创建了一个实例出来完毕后，另一个线程获得锁进入该同步代码，实例已经存在，没必要再次创建，因此这个判断是否是null还是必须的。
• 我一般用在工具类的创建上
• `

工厂模式

public class FragmentFactory {
    private static HashMap hashMap = new HashMap();
    private static int currentPosition;

    public static BaseFragment createFragment(int position) {
        //根据传递进来的索引去生成Fragment(内存缓存获取,直接new)
        BaseFragment fragment = hashMap.get(position);
        currentPosition = position;
        if (fragment != null) {
            return fragment;
        } else {
            switch (position) {
                case 4:
                    fragment = new SelectProductFragment();
                    break;
                case 0:
                    fragment = new StartFragment();
                    break;
                case 1:
                    //创建首页对应的Fragment对象
                    //每一个Fragment都是在onCreatView方法中返回界面view效果
                    fragment = new AppointFragment();
                    break;
                case 2:
                    fragment = new PackageFragment();
                    break;
                case 5:
                    fragment = new ReportFormFragment();
                    break;
                case 6:
                    fragment = new CaddieManageFragment();
                    break;

                case 3:
                    fragment = new CarInfWebViewFragment();
                    break;
                case 7:
                    fragment = new Start2Fragment();
                    break;

            }
            //生成了fragment对象后,需要将其加入内存中hashMap
            hashMap.put(position, fragment);
            return fragment;
        }
    }


}

• 工厂模式可以用在用在页面缓存.

Build模式

package com.example.king.designpatternsdemoforandroid;

/**
 * Created by king on 2017/3/9.
 */
public class Person {
    private String name;
    private int age;
    private double height;
    private double weight;

    private Person(Builder builder) {
        this.name=builder.name;
        this.age=builder.age;
    }
    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;
    }

    static class Builder{
        private String name;
        private int age;

        public Person build(){
            return new Person(this);
        }
        public Builder name(String name){
            this.name=name;
            return this;
        }
        public Builder age(int age){
            this.age=age;
            return this;
        }

    }
}

调用方式

  Person.Builder person = new Person.Builder();
                person.age(1).name("11");

---

Builder模式是不是也很面熟?是的,我们的AlertDialog就是这样子写的

 AlertDialog.Builder builder=new AlertDialog.Builder(this);
        AlertDialog dialog=builder.setTitle("标题")
                .setIcon(android.R.drawable.xx)
                .setView(R.layout.xx)
                .setPositiveButton("确定", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {

                    }
                })
                .setNegativeButton("取消", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {

                    }
                })
                .create();
        dialog.show();

还有StringBuilder

  StringBuilder builder = new StringBuilder();
        builder.append("aa").append("bb");

原型模式

研究过浅拷贝和深拷贝的人对这样的例子一定不陌生

package com.example.king.designpatternsdemoforandroid;
/**
 * Created by king on 2017/3/9.
 */
public class Person2 implements Cloneable{
    private String name;
    private int age;
    private double height;
    private double weight;

    public Person2(){

    }

    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 +
                '}';
    }

    @Override
    public Object clone(){
        Person2 person=null;
        try {
            person=(Person2)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;
    }
}

调用

        Person2 p=new Person2();
        p.setAge(18);
        p.setName("张三");
        p.setHeight(178);
        p.setWeight(65);
        System.out.println(p);

        Person2 p1= (Person2) p.clone();
        System.out.println(p1);

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

结果

System.out: Person{name='张三', age=18, height=178.0, weight=65.0}
System.out: Person{name='张三', age=18, height=178.0, weight=65.0}
System.out: Person{name='张三', age=18, height=178.0, weight=65.0}
System.out: Person{name='李四', age=18, height=178.0, weight=65.0}

其实这就是一个原型模式

我们经常用的Intent就是一个原型模式的使用者

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

/** 
 * Copy constructor. 
 */  
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;  
    if (o.mCategories != null) {  
        this.mCategories = new ArraySet(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);  
    }  
}