24Observer样式应用于Android框架设计.doc

24.Observer样式应用于Android框架设计1.Framework的反向控制反向控制(InversionofControl)是应用框架(ApplicationFramework，简称AF)魅力的泉源。其常见的实现机制有二：1)继承(Inheritance)-这与TemplateMethod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TemplateMethod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TemplateMethod样式)兹复习你已经熟悉的TemplateMethod样式，如下述之范例：/Student.javapublicclassStudentprivateStringm_name；privateintm_credit；Student(Stringna,intcr)m_name=na；m_credit=cr；publicvoidprint()System.out.println(m_name+,+String.valueOf(template_computeTuition()；publicfloattemplate_computeTuition()if(m_credit6)m_credit=6；returnhook_getValue(m_credit)+5000；protectedfloathook_getValue(intcredit)return(credit-1)*500；/Graduate_Student.javapublicclassGraduate_StudentextendsStudentGraduate_Student(Stringna,intcr)super(na,cr)；protectedfloathook_getValue(intcredit)returncredit*700；/Undergraduate_Student.javapublicclassUndergraduate_StudentextendsStudentUndergraduate_Student(Stringna,intcr)super(na,cr)；/JMain.javapublicclassJMainpublicstaticvoidmain(Stringargs)intcredit=5；Graduate_Studentmike=newGraduate_Student(Mike,5)；mike.print()；Undergraduate_Studentlinda=newUndergraduate_Student(Linda,7)；linda.print()；这是以TemplateMethod样式来实践反向控制。3.使用委托(即Observer样式)在TemplateMethod样式里，hookmethod的具体实现是撰写在子类别里。使用委托时，则将hookmethod定义于独立的类别里，如下述的HookClass：把hookmethod定义于另外的类别：/HookClass.javapublicclassHookClassprotectedfloatgetValue(intcredit)return(credit-1)*500；templatemethod委托HookClass类别之对象去处理客制化的部份：/Student.javapublicclassStudentprivateStringm_name；privateintm_credit；privateHookClasshookObject=null；Student(Stringna,intcr)m_name=na；m_credit=cr；publicvoidsetHook(HookClasshk)hookObject=hk；publicvoidprint()System.out.println(m_name+,+String.valueOf(template_computeTuition()；publicfloattemplate_computeTuition()if(m_credit6)m_credit=6；returnhookObject.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.javapublicclassGraduate_StudentextendsStudentGraduate_Student(Stringna,intcr)super(na,cr)；setHook(newGraduateHook()；privatestaticclassGraduateHookextendsHookClassOverrideprotectedfloatgetValue(intcredit)returncredit*700；/JMain.javapublicclassJMainpublicstaticvoidmain(Stringargs)intcredit=5；Studentmike=newGraduate_Student(Mike,credit)；mike.print()；于是，Student类别的templatemethod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1Observer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.javapublicinterfaceIListenerfloatgetValue(intcredit)；/Student.javapublicclassStudentprivateStringm_name；privateintm_credit；privateIListenerplis=null；Student(Stringna,intcr)m_name=na；m_credit=cr；publicvoidsetListener(IListenerlis)plis=lis；publicvoidprint()System.out.println(m_name+,+String.valueOf(template_computeTuition()；publicfloattemplate_computeTuition()if(m_credit6)m_credit=6；returnplis.getValue(m_credit)+5000；/Graduate_Student.javapublicclassGraduate_StudentextendsStudentGraduate_Student(Stringna,intcr)super(na,cr)；setListener(newGraduateListener()；privatestaticclassGraduateListenerimplementsIListenerpublicfloatgetValue(intcredit)returncredit*700；/JMain.javapublicclassJMainpublicstaticvoidmain(Stringargs)intcredit=5；Studentmike=newGraduate_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.javapackagecom.misoo.pkzz；importandroid.app.Activity；importandroid.os.Bundle；importandroid.view.View；importandroid.view.View.OnClickListener；importandroid.widget.Button；publicclassac01extendsActivityOverridepublicvoidonCreate(Bundleicicle)super.onCreate(icicle)；setContentView(R.layout.main)；Buttonbtn=(Button)findViewById(R.id.button)；Buttonbtn2=(Button)findViewById(R.id.button2)；btn.setBackgroundResource(R.drawable.gray)；btn.setOnClickListener(clickListener)；btn2.setBackgroundResource(R.drawable.byw)；btn2.setOnClickListener(clickListener_2)；OnClickListenerclickListener=newOnClickListener()publicvoidonClick(Viewv)Stringname=(Button)v).getText().toString()；setTitle(name+buttonc