C# 即時監控 CPU 使用率：PerformanceCounter 與多核心支援完整實作

核心元件：PerformanceCounter

System.Diagnostics.PerformanceCounter 提供存取 Windows 效能計數器資料。監控 CPU 使用率需設定：

• CategoryName = "Processor"
• CounterName = "% Processor Time"
• InstanceName = "_Total"（所有核心平均）或 "0"、"1"...（單核心）

WinForms 完整實作

public partial class CpuMonitorForm : Form {
    private readonly PerformanceCounter _cpuCounter;
    private readonly Timer _timer;

    public CpuMonitorForm() {
        InitializeComponent();
        _cpuCounter = new PerformanceCounter("Processor", "% Processor Time", "_Total", true);
        _timer = new Timer { Interval = 1000 };
        _timer.Tick += Timer_Tick;
        _timer.Start();
    }

    private void Timer_Tick(object sender, EventArgs e) {
        float cpu = _cpuCounter.NextValue(); // 首次呼叫回傳 0，後續為百分比
        progressBar1.Value = Math.Min(100, (int)cpu);
        label1.Text = $"CPU 使用率：{cpu:F1}%";
    }

    protected override void Dispose(bool disposing) {
        if (disposing) {
            _timer?.Dispose();
            _cpuCounter?.Dispose();
        }
        base.Dispose(disposing);
    }
}

多核心動態監控擴充

private void InitializeMultiCoreMonitor() {
    int coreCount = Environment.ProcessorCount;
    var counters = new PerformanceCounter[coreCount];
    var bars = new ProgressBar[coreCount];
    var labels = new Label[coreCount];

    for (int i = 0; i < coreCount; i++) {
        counters[i] = new PerformanceCounter("Processor", "% Processor Time", i.ToString(), true);
        // 動態建立 UI：GroupBox 包含 Label + ProgressBar
        var gb = new GroupBox { Text = $"Core {i}", Dock = DockStyle.Top, Height = 60 };
        bars[i] = new ProgressBar { Dock = DockStyle.Fill, Maximum = 100 };
        labels[i] = new Label { Dock = DockStyle.Right, Width = 60, TextAlign = ContentAlignment.MiddleRight };
        gb.Controls.Add(bars[i]); gb.Controls.Add(labels[i]);
        panelContainer.Controls.Add(gb);
    }

    var timer = new Timer { Interval = 1000 };
    timer.Tick += (s, e) => {
        for (int i = 0; i < coreCount; i++) {
            float v = counters[i].NextValue();
            bars[i].Value = Math.Min(100, (int)v);
            labels[i].Text = $"{v:F1}%";
        }
    };
    timer.Start();
}

進階：Dundas Gauge / Circular ProgressBar 視覺化

替換 ProgressBar 為第三方儀表控制項（如 Dundas Gauge、LiveCharts、Microcharts），即可呈現儀表板風格 CPU 監控。

權限與部署注意

• 需「效能監視使用者」群組權限或管理員權限讀取計數器
• ASP.NET / 服務帳戶需加入 Performance Monitor Users 群組
• 遠端監控：new PerformanceCounter(..., machineName: "Server01")
• NextValue() 首次呼叫回傳 0，建議啟動時呼叫一次捨棄

替代方案：System.Management (WMI)

var searcher = new ManagementObjectSearcher("SELECT LoadPercentage FROM Win32_Processor");
foreach (var obj in searcher.Get()) {
    Console.WriteLine($"CPU Load: {obj["LoadPercentage"]}%");
}

WMI 查詢較慢，適合低頻輪詢；PerformanceCounter 適合高頻即時顯示。