1. Line5~8:宣告四種委派定義(加、減、乘、除)
2. Line9~12: 四個委派物件(加、減、乘、除)
3. Line16~19: 在MultiplyUC()創建子階段就初始化四個物件，以匿名函式實體化之。
4. Line 29: 判斷運算子的選擇
5. Line32~41:呼叫四種委派物件(運算子)
1: namespace DelegateDemo
2: {3: public partial class MultiplyUC : UserControl
4: {5: public delegate double Multiply(double x, double y);
6: public delegate double Divide(double x, double y);
7: public delegate double Add(double x, double y);
8: public delegate double Sub(double x, double y);
9: Add addOP; 10: Sub subOP; 11: Multiply mulOP; 12: Divide divOP;13: public MultiplyUC()
14: { 15: InitializeComponent();16: addOP = delegate (double x, double y) { return x + y; };
17: subOP = delegate (double x, double y) { return x - y; };
18: mulOP = delegate (double x, double y) { return x * y; };
19: divOP = delegate (double x, double y) { return x / y; };
20: } 21: 22: private void calcBtn_Click(object sender, EventArgs e)
23: {24: if (opCBox.SelectedIndex < 0) MessageBox.Show("Please select an operator at least.");
25: double x, y, z;
26: double.TryParse(XTBox.Text, out x);
27: double.TryParse(YTBox.Text, out y);
28: 29: switch (opCBox.SelectedIndex)
30: {31: case 0:
32: z = addOP(x, y);33: break;
34: case 1:
35: z = subOP(x, y);36: break;
37: case 2:
38: z = mulOP(x, y);39: break;
40: case 3:
41: z = divOP(x, y);42: break;
43: default:
44: z = 0;45: break;
46: } 47: resultLbl.Text = z.ToString(); 48: } 49: } 50: }直接拉四份自製User Control物件MultiplyUC至Form1
執行結果
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新增Operations.cs
1. Line 1:定義委派dOperation
2. Operations運算類別，包含兩個私有_numberA 和 _numberB，以及可以再衍生類別實體化的委派op
3. 虛擬函式Calculate()，執行委派op(NumberA, NumberB)並將結果傳回
1: public delegate double dOperation(double a, double b);
2: public class Operations
3: {4: private double _numberA = 0;
5: private double _numberB = 0;
6: protected dOperation op;
7: public double NumberA { get { return _numberA; }set { _numberA = value; } }
8: public double NumberB { get { return _numberB; } set { _numberB = value; } }
9: 10: public virtual double Calculate()
11: {12: double result = 0;
13: result = op(NumberA, NumberB);14: return result;
15: } 16: }接下來定義四個類別(加、減、乘、除)，都是繼承自Operations
以加法為例
1. 定義加法Add方法
2. Line 4~9:重新覆寫父類別虛擬方法，首先實體化父類別中op委派，指向Add方法
3. Line 7: 執行父類別 base.Calculate()，相當於執行Add(a, b);
1: class OperationAdd:Operations
2: {3: private double Add(double a, double b) { return a + b; }
4: public override double Calculate()
5: {6: op = new dOperation(Add);
7: return base.Calculate();
8: } 9: }其他四則運算相似，先定義各自方法，在實體化父類別op委派，最後呼叫父類別Calculate進行運算。
1: class OperationSub:Operations
2: {3: private double Subtract(double a, double b) { return a - b; }
4: public override double Calculate()
5: {6: op = new dOperation(Subtract);
7: return base.Calculate();
8: } 9: }10: class OperationMul : Operations
11: {12: private double Multiply(double a, double b) { return a * b; }
13: public override double Calculate()
14: {15: op = new dOperation(Multiply);
16: return base.Calculate();
17: } 18: }19: class OperationDiv : Operations
20: {21: private double Divide(double a, double b) { return a / b; }
22: public override double Calculate()
23: {24: if (NumberB == 0)
25: {26: throw new Exception("除數不可以為零");
27: }28: op = new dOperation(Divide);
29: return base.Calculate();
30: } 31: }簡單工廠模式
1. Line 3: 靜態函式CreateOperations根據輸入字串(運算子)決定產生何種實體
2. Line9, 12, 15和18: 利用多型(Polymorphism)觀念，OperationAdd()、OperationSub()、OperationMul、或是OperationDiv，皆可以存回父類別Operations物件op
3. 使用 class 的靜態方法，依不同條件，取得不同物件，並用取得的物件，做類似的事情。缺點是要新增不同條件時，須修改到類別的靜態方法。
4. 第3點簡單工廠模式(Simple Factory Pattern)的缺點，可以透過工廠方法模式(Factory Method Pattern)改善
1: public class OperationsFactory
2: {3: public static Operations CreateOperations(string operation)
4: {5: Operations op = null;
6: switch(operation)
7: {8: case "+":
9: op = new OperationAdd();
10: break;
11: case "-":
12: op = new OperationSub();
13: break;
14: case "*":
15: op = new OperationMul();
16: break;
17: case "/":
18: op = new OperationDiv();
19: break;
20: }21: return op;
22: } 23: }
參考資料
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