委託(delegate)和事件(event)

委託必須和欲委託的方法有同樣的參數

委託就是一個類，任何可以聲明類的地方都可以聲明委託

 

定義事件的四個步驟：

    在事件發行者中定義事件

    在事件發行者中觸發事件

    在事件訂閱者中定義事件處理程序（必須和委託類型相一致）

    向事件發行者訂閱一個事件

 

 using system; class publisher { public delegate void pubcomputer(string magazinename); public delegate void publife(string magazinename); public event pubcomputer onpubcomputer; public event publife onpublife; public void issuecomputer() { if (onpubcomputer!=null) { console.writeline("發行《電腦》雜誌"); onpubcomputer("《電腦》雜誌"); } } public void issuelife() { if (onpublife!=null) { console.writeline("發行《生活》雜誌"); onpublife("《生活》雜誌"); } } } class subscriber { private string name; public subscriber(string name) { this.name=name; } public void receive(string magazinename) { console.writeline(name+"已收到"+magazinename); } } class story { static void main() { publisher pub=new publisher(); subscriber zs=new subscriber("張三"); pub.onpubcomputer+=new publisher.pubcomputer(zs.receive); subscriber ls=new subscriber("李四"); pub.onpubcomputer+=new publisher.pubcomputer(ls.receive); pub.onpublife+=new publisher.publife(ls.receive); pub.issuecomputer(); pub.issuelife(); console.writeline(); console.writeline("一年後"); pub.onpubcomputer-=new publisher.pubcomputer(ls.recevice); pub.issuecomputer(); pub.issuelife(); } }

 

事件設計準則：

    事件的命名準則應使用PascalCasing命名方式

    聲明DELEGATE時，使用VOID類型當返回值，EventName事件的事件委託是EventNameEventHandler，事件接受兩個傳入參數，一律命名爲sender和e

    定義一個提供事件數據的類。對類以EventNameEventArgs進行命名，從system.EventArgs派生該類，然後添加所有事件特定的成員。

public delegate void EventNameEventHandler(onject sender,EventArgs e);

public event EventNameEventHandler EventName;

 

下面是根據事件設計準則規範以後的代碼

using system; class PubEventArgs : EventArgs { private readonly string m_magazineName; private readonly DateTime m_pubDate; public PubEventArgs(string magazineName,DateTime pubDate) { m_magazineName=magazineName m_pubDate=pubDate; } public string magazineName { get { return m_magazineName;} } public DateTime pubDate { get { return m_pubDate;} } } class publisher { public delegate void pubcomputerEventHandler(object sender pubEventArgs e); public delegate void publifeEventHandler(object sender pubEventArgs e); public event pubcomputerEventHandler onpubcomputer; public event publifeEventHandler onpublife; protected virtual void OnPubComputer(PubEventArgs e) { pubComputerEventHandler handler=PubComputer; if (handler!=null) { handler(this,e); } } protected virtual void OnPubLife(PubEventArgs e) { pubLifeEventHandler handler=PubLife; if (handler!=null) { handler(this,e); } } public void issuecomputer(string magazineName,DateTime pubDate) { console.writeline("發行了"+magazineName); OnPubComputer(new PubEventArgs(magazineName,pubDate)); } public void issuelife(string magazineName,DateTime pubDate) { console.writeline("發行了"+magazineName); OnPubLife(new PubEventArgs(magazineName,pubDate)); } } class subscriber { private string name; public subscriber(string name) { this.name=name; } public void receive(onject sender,pubEventArgs e) { console.writeline(e.pubDate+" "+name+"已收到"+e.magazinename); } } class story { static void main() { publisher pub=new publisher(); subscriber zs=new subscriber("張三"); pub.onpubcomputer+=new publisher.pubcomputerEventHandler(zs.receive); subscriber ls=new subscriber("李四"); pub.onpubcomputer+=new publisher.pubcomputerEventHandler(ls.receive); pub.onpublife+=new publisher.publifeEventHandler(ls.receive); pub.issuecomputer("電腦雜誌",Convert.ToDateTime("2007-1-1")); pub.issuelife("生活雜誌",Convert.ToDateTime("2007-1-1")); console.writeline(); console.writeline("一年後"); pub.onpubcomputer-=new publisher.pubcomputerEventHandler(ls.recevice); pub.issuecomputer("電腦雜誌",Convert.ToDateTime("2008-1-1")); pub.issuelife("生活雜誌",Convert.ToDateTime("2008-1-1")); } }