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");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);
}
}