Observer样式应用于Android框架设计.doc

Observer样式应用于Android框架设计1. Framework的反向控制反向控制(Inversion of Control)是应用框架(Application Framework，简称AF)魅力的泉源。其常见的实现机制有二：1) 继承(Inheritance)- 这与Template Method样式密切相关。2) 委托(Delegation)- 这与Observer样式密切相关。 Android是个完全的AF，处处可见到反向控制的机制。当你熟悉上述的两种实现机制后，就会将之对应到Template Method和Observer样式。然后藉由样式来更深刻体会这些机制的设计意涵。如此，除了更能活用Android之外，也能逐渐提升你自己设计新AF的兴趣、能力和信心。2. 复习：使用继承(即Template Method样式)兹复习你已经熟悉的Template Method样式，如下述之范例： / Student.javapublic class Student private String m_name;private int m_credit;Student(String na, int cr )m_name = na;m_credit = cr;public void print()System.out.println(m_name + , +String.valueOf(template_computeTuition(); public float template_computeTuition() if (m_credit 6) m_credit = 6; return hook_getValue(m_credit) + 5000; protected float hook_getValue(int credit) return (credit -1) * 500; / Graduate_Student.javapublic class Graduate_Student extends StudentGraduate_Student(String na, int cr )super(na, cr);protected float hook_getValue(int credit) return credit * 700;/ Undergraduate_Student.javapublic class Undergraduate_Student extends Student Undergraduate_Student(String na, int cr )super(na, cr);/ JMain.javapublic class JMain public static void main(String args) int credit = 5;Graduate_Student mike = new Graduate_Student(Mike, 5);mike.print();Undergraduate_Student linda = new Undergraduate_Student(Linda, 7);linda.print();这是以Template Method样式来实践反向控制。3. 使用委托(即Observer样式)在Template Method样式里，hook method的具体实现是撰写在子类别里。使用委托时，则将hook method定义于独立的类别里，如下述的HookClass：把hook method定义于另外的类别：/ HookClass.javapublic class HookClass protected float getValue(int credit) return (credit -1) * 500; template method委托HookClass类别之对象去处理客制化的部份：/ Student.javapublic class Student private String m_name;private int m_credit;private HookClass hookObject = null;Student(String na, int cr )m_name = na;m_credit = cr;public void setHook(HookClass hk)hookObject = hk;public void print()System.out.println(m_name + , +String.valueOf(template_computeTuition(); public float template_computeTuition() if (m_credit 6) m_credit = 6; return hookObject.getValue(m_credit) + 5000; 定义HookClass的子类别：GraduateHook，并且让Student的对象委托给GraduateHook子类别之对象：/ Graduate_Student.javapublic class Graduate_Student extends StudentGraduate_Student(String na, int cr )super(na, cr);setHook(new GraduateHook();private static class GraduateHook extends HookClassOverrideprotected float getValue(int credit) return credit * 700;/ JMain.javapublic class JMain public static void main(String args) int credit = 5; Student mike = new Graduate_Student(Mike, credit);mike.print(); 于是，Student类别的template method 呼叫了HookClass抽象类别的getValue()函数，进而反向呼叫到GraduateHook子类别的getValue()函数。4. GoF的Observer样式在GoF的一书里，其Observer样式的架构图为：图1 Observer样式GoF这里的Subject类别就对应到上述程序代码的Student类别。ConcreteSubject就对应到Graduate_Student类别。Observer类别对应到HookClass。ConcreteObserver对应到GraduateHook类别。5. Observer样式又称为Listener样式 上述的范例可改写为：/ IListener.javapublic interface IListener float getValue(int credit);/ Student.javapublic class Student private String m_name;private int m_credit;private IListener plis = null;Student(String na, int cr )m_name = na;m_credit = cr;public void setListener(IListener lis)plis = lis;public void print()System.out.println(m_name + , +String.valueOf(template_computeTuition(); public float template_computeTuition() if (m_credit 6) m_credit = 6; return plis.getValue(m_credit) + 5000; / Graduate_Student.javapublic class Graduate_Student extends StudentGraduate_Student(String na, int cr )super(na, cr);setListener(new GraduateListener();private static class GraduateListener implements IListenerpublic float getValue(int credit) return credit * 700;/ JMain.javapublic class JMain public static void main(String args) int credit = 5; Student mike = new Graduate_Student(Mike, credit);mike.print(); 6. 欣赏Android里的Observer样式(即Listener样式)- 欣赏Android程序范例6.1 画面情境 撰写程序 建立Android程序项目：/ ac01.javapackage com.misoo.pkzz;import android.app.Activity;import android.os.Bundle;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;public class ac01 extends Activity Override public void onCreate(Bundle icicle) super.onCreate(icicle); setContentView(R.layout.main); Button btn = (Button)findViewById(R.id.button); Button btn2 = (Button)findViewById(R.id.button2); btn.setBackgroundResource(R.drawable.gray); btn.setOnClickListener(clickListener); btn2.setBackgroundResource(R.drawable.byw); btn2.setOnClickListener(clickListener_2); OnClickListener clickListener = new OnClickListener() public void onClick(View v) String name = (Button)v).getText().toString(); setTitle( name + button cl