C# 委托與事件詳解（六）

運行無誤，輸出雙語問候。若需將多方法綁定同一委托：

static void Main() {
    GreetingManager gm = new GreetingManager();
    GreetingDelegate delegate1;
    delegate1 = EnglishGreeting;
    delegate1 += ChineseGreeting;
    gm.GreetPeople("Jimmy Zhang", delegate1);
}

輸出兩次 "Jimmy Zhang"。為方便客戶端，嘗試將委托封裝進 GreetingManager：

public class GreetingManager {
    public GreetingDelegate delegate1;
    public void GreetPeople(string name, GreetingDelegate MakeGreeting) {
        MakeGreeting(name);
    }
}

客戶端：

gm.delegate1 = EnglishGreeting;
gm.delegate1 += ChineseGreeting;
gm.GreetPeople("Jimmy Zhang", gm.delegate1);

調用時仍需傳遞 gm.delegate1 顯得多餘。改進：

public class GreetingManager {
    public GreetingDelegate delegate1;
    public void GreetPeople(string name) {
        if (delegate1 != null) delegate1(name);
    }
}

客戶端簡化為 gm.GreetPeople("Jimmy Zhang")。但仍存問題：delegate1 為 public 欄位，客戶端可任意賦值破壞封裝，且 =/+= 語法不一致。