24.Observer樣式應用于Android框架設計1.Framework的反向控制反向控制(InversionofControl)是應用框架(ApplicationFramework，簡稱AF)魅力的泉源。其常見的實現(xiàn)機制有二：1)繼承(Inheritance)-這與TemplateMethod樣式密切相關。2)委托(Delegation)-這與Observer樣式密切相關。Android是個完全的AF，處處可見到反向控制的機制。當你熟悉上述的兩種實現(xiàn)機制后，就會將之對應到TemplateMethod和Observer樣式。然后藉由樣式來更深刻體會這些機制的設計意涵。如此，除了更能活用Android之外，也能逐漸提升你自己設計新AF的興趣、能力和信心。2.復習：使用繼承(即TemplateMethod樣式)茲復習你已經(jīng)熟悉的TemplateMethod樣式，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()；這是以TemplateMethod樣式來實踐反向控制。3.使用委托(即Observer樣式)在TemplateMethod樣式里，hookmethod的具體實現(xiàn)是撰寫在子類別里。使用委托時，則將hookmethod定義于獨立的類別里，如下述的HookClass：把hookmethod定義于另外的類別：/HookClass.javapublicclassHookClassprotectedfloatgetValue(intcredit)return(credit-1)*500；templatemethod委托HookClass類別之對象去處理客制化的部份：/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；定義HookClass的子類別：GraduateHook，并且讓Student的對象委托給GraduateHook子類別之對象：/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類別的templatemethod呼叫了HookClass抽象類別的getValue()函數(shù)，進而反向呼叫到GraduateHook子類別的getValue()函數(shù)。4.GoF的Observer樣式在GoF的一書里，其Observer樣式的架構圖為：圖1Observer樣式GoF這里的Subject類別就對應到上述程序代碼的Student類別。ConcreteSubject就對應到Graduate_Student類別。Observer類別對應到HookClass。ConcreteObserver對應到GraduateHook類別。5.Observer樣式又稱為Listener樣式上述的范例可改寫為：/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.欣賞Android里的Observer樣式(即Listener樣式)-欣賞Android程序范例6.1畫面情境撰寫程序建立Android程序項目：/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