C# 委派應用：表單按鈕綁定多種輸出行為

表單欄位與初始化

private readonly ProcessNumber _pn = new ProcessNumber(100);
private ShowNumberDel _del;

private void Form1_Load(object sender, EventArgs e)
{
    // _pn 已在欄位初始化器建立
}

三種輸出實作方法

// 1. Console
private void ShowInConsole(object[] items)
{
    foreach (var item in items) Console.WriteLine(item);
}

// 2. ListBox
private void ShowInListBox(object[] items)
{
    listBox1.Items.Clear();
    foreach (var item in items) listBox1.Items.Add(item);
}

// 3. Text File
private void ShowInFile(object[] items)
{
    using var sw = new StreamWriter("Test.txt", true);
    foreach (var item in items) sw.WriteLine(item);
}

按鈕事件綁定

// 單一策略
private void button1_Click(object sender, EventArgs e) =>
    _pn.ProcessItems(new ShowNumberDel(ShowInConsole));

private void button2_Click(object sender, EventArgs e) =>
    _pn.ProcessItems(new ShowNumberDel(ShowInListBox));

private void button3_Click(object sender, EventArgs e) =>
    _pn.ProcessItems(new ShowNumberDel(ShowInFile));

// 組合策略：多播委派
private void button4_Click(object sender, EventArgs e)
{
    _del = null; // 重置
    _del += new ShowNumberDel(ShowInListBox);
    _del += new ShowNumberDel(ShowInFile);
    _pn.ProcessItems(_del);
}

設計重點

• 關注點分離：處理邏輯 (`ProcessNumber`) 不知輸出細節
• 執行時期組合：按鈕決定輸出組合，無需修改處理類別
• 開放封閉：新增輸出目標（如 Database、Network）只需新增方法並綁定