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<Integer, BaseFragment> hashMap = new HashMap<Integer, BaseFragment>(); 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");

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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<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); } }