C# Windows Forms 入門三部曲：從建立表單到溫度轉換完整實作

前言

C# 是 .NET Framework 的核心開發語言，配合 System.Windows.Forms 命名空間可快速建立桌面應用程式。本文以「攝氏/華氏溫度轉換器」為例，完整示範 WinForms 開發的三大步驟：建立表單、配置控制項、撰寫事件處理邏輯。

開發環境

• .NET Framework SDK（Beta 1 或正式版）
• 文字編輯器 + 命令列編譯器（csc.exe），或 Visual Studio .NET

第一步：建立主表單

繼承 System.Windows.Forms.Form，在建構子中設定視覺屬性：

public class TempConverter : System.Windows.Forms.Form
{
    public TempConverter()
    {
        // 視窗尺寸與行為
        this.ClientSize = new System.Drawing.Size(180, 90);
        this.FormBorderStyle = FormBorderStyle.FixedDialog;
        this.Text = "°C → °F / °F → °C";
        this.StartPosition = FormStartPosition.CenterScreen;
        this.MaximizeBox = false;
        this.HelpButton = false;
    }

    [STAThread]
    public static void Main()
    {
        Application.Run(new TempConverter());
    }
}

編譯指令：

csc /r:System.dll /r:System.Windows.Forms.dll /r:System.Drawing.dll TempConverter.cs

第二步：加入控制項

宣告欄位、實例化、設定屬性、加入 Controls 集合：

public class TempConverter : System.Windows.Forms.Form
{
    // 控制項欄位
    private Label lblC = new Label();
    private Label lblF = new Label();
    private TextBox txtC = new TextBox();
    private TextBox txtF = new TextBox();
    private Button btnCtoF = new Button();
    private Button btnFtoC = new Button();

    public TempConverter()
    {
        // ... 表單屬性設定同上 ...

        // 攝氏輸入區
        txtC.TabIndex = 0; txtC.Size = new Size(50, 25); txtC.Location = new Point(13, 5);
        lblC.TabStop = false; lblC.Text = "°C"; lblC.Size = new Size(25, 25); lblC.Location = new Point(65, 5);

        // 華氏輸入區
        txtF.TabIndex = 1; txtF.Size = new Size(50, 25); txtF.Location = new Point(90, 5);
        lblF.TabStop = false; lblF.Text = "°F"; lblF.Size = new Size(25, 25); lblF.Location = new Point(142, 5);

        // 轉換按鈕
        btnCtoF.TabIndex = 2; btnCtoF.Text = "°C → °F"; btnCtoF.Size = new Size(70, 25); btnCtoF.Location = new Point(13, 35);
        btnFtoC.TabIndex = 3; btnFtoC.Text = "°F → °C"; btnFtoC.Size = new Size(70, 25); btnFtoC.Location = new Point(90, 35);

        // 事件訂閱
        btnCtoF.Click += new EventHandler(btnCtoF_Click);
        btnFtoC.Click += new EventHandler(btnFtoC_Click);

        // 加入表單
        this.Controls.AddRange(new Control[] { txtC, lblC, txtF, lblF, btnCtoF, btnFtoC });
    }
    // ... 事件處理方法見下節 ...
}

第三步：實作事件處理邏輯

攝氏轉華氏

private void btnCtoF_Click(object sender, EventArgs e)
{
    if (!double.TryParse(txtC.Text, out double c))
    {
        txtC.Clear(); txtF.Clear();
        return;
    }
    double f = 1.8 * c + 32;
    txtF.Text = f.ToString("F2"); // 保留兩位小數
    txtF.Focus();
    txtF.Select(0, 0); // 游標移至開頭
}

華氏轉攝氏

private void btnFtoC_Click(object sender, EventArgs e)
{
    if (!double.TryParse(txtF.Text, out double f))
    {
        txtC.Clear(); txtF.Clear();
        return;
    }
    double c = (f - 32) / 1.8;
    txtC.Text = c.ToString("F2");
    txtC.Focus();
    txtC.Select(0, 0);
}

完整程式碼整理

using System;
using System.Windows.Forms;

public class TempConverter : Form
{
    private Label lblC = new Label(), lblF = new Label();
    private TextBox txtC = new TextBox(), txtF = new TextBox();
    private Button btnCtoF = new Button(), btnFtoC = new Button();

    public TempConverter()
    {
        ClientSize = new Size(180, 90);
        FormBorderStyle = FormBorderStyle.FixedDialog;
        Text = "°C → °F / °F → °C";
        StartPosition = FormStartPosition.CenterScreen;
        MaximizeBox = false; HelpButton = false;

        txtC.TabIndex = 0; txtC.Size = new Size(50, 25); txtC.Location = new Point(13, 5);
        lblC.TabStop = false; lblC.Text = "°C"; lblC.Size = new Size(25, 25); lblC.Location = new Point(65, 5);
        txtF.TabIndex = 1; txtF.Size = new Size(50, 25); txtF.Location = new Point(90, 5);
        lblF.TabStop = false; lblF.Text = "°F"; lblF.Size = new Size(25, 25); lblF.Location = new Point(142, 5);
        btnCtoF.TabIndex = 2; btnCtoF.Text = "°C → °F"; btnCtoF.Size = new Size(70, 25); btnCtoF.Location = new Point(13, 35);
        btnFtoC.TabIndex = 3; btnFtoC.Text = "°F → °C"; btnFtoC.Size = new Size(70, 25); btnFtoC.Location = new Point(90, 35);

        btnCtoF.Click += btnCtoF_Click;
        btnFtoC.Click += btnFtoC_Click;

        Controls.AddRange(new Control[] { txtC, lblC, txtF, lblF, btnCtoF, btnFtoC });
    }

    [STAThread]
    static void Main() => Application.Run(new TempConverter());

    private void btnCtoF_Click(object sender, EventArgs e)
    {
        if (!double.TryParse(txtC.Text, out double c)) { txtC.Clear(); txtF.Clear(); return; }
        txtF.Text = (1.8 * c + 32).ToString("F2");
        txtF.Focus(); txtF.Select(0, 0);
    }

    private void btnFtoC_Click(object sender, EventArgs e)
    {
        if (!double.TryParse(txtF.Text, out double f)) { txtC.Clear(); txtF.Clear(); return; }
        txtC.Text = ((f - 32) / 1.8).ToString("F2");
        txtC.Focus(); txtC.Select(0, 0);
    }
}

關鍵概念總結

進階延伸建議

• 使用 TableLayoutPanel 或 FlowLayoutPanel 取代絕對座標，支援 DPI 縮放與多語系。
• 加入 ErrorProvider 顯示輸入驗證錯誤圖示。
• 將轉換邏輯抽離為獨立靜態類別（TemperatureConverter），符合單一職責原則。
• 使用資料繫結配合 INotifyPropertyChanged 實現 MVVM 風格架構。