#眉標=Windows Form
#副標=Windows Form UI優化入門課
#大標=實作非同步作業
#作者=文／圖	李明儒



==<box>===========
程式1
private void Form1_Load(object sender, 
    EventArgs e)
{
    //預設為暫存目錄
    txtPath.Text = Path.GetTempPath();
}

private int fileCount = 0;
private long totalSize = 0;

private void btnGO_Click(object sender, 
    EventArgs e)
{
    //重設統計數據
    fileCount = 0;
    totalSize = 0;
    //統計檔案數及大小
    explore(txtPath.Text);
    //顯示結果
    lblResult.Text = string.Format(
        "{0:#,##0} files, {1:#,##0} bytes",
        fileCount, totalSize);
}

private void explore(string path)
{
    //使用遞迴搜索所有目錄
    foreach (string dir in 
        Directory.GetDirectories(path))
        explore(dir);
    foreach (string file in 
        Directory.GetFiles(path))
    {
        fileCount++;
        //加總檔案大小
        FileInfo fi = new FileInfo(file);
        totalSize += fi.Length;
    }
}

private void timer1_Tick(object sender, 
    EventArgs e)
{
    //每隔50ms顯示最新時間
    toolStripStatusLabel1.Text =
        DateTime.Now.ToString("HH:mm:ss.fff");
}==<end>==============



	
==<box>===========
程式2
private void btnGO_Click(object sender, EventArgs e)
{
    //將統計作業排入ThreadPool Queue
    //Windows會另開Thread處理，UI Thread可以
    //繼續處理UI畫面顯示並與使用者互動
    ThreadPool.QueueUserWorkItem(
        new WaitCallback(startJob), txtPath.Text);
}

private void startJob(object path)
{
    fileCount = 0;
    totalSize = 0;
    explore(path.ToString());
    //***以下這行有點問題***
    lblResult.Text = string.Format(
        "{0:#,##0} files, {1:#,##0} bytes",
        fileCount, totalSize);
}==<end>==============



==<灰>===========
InvalidOperationException was unhandled
Cross-thread operation not valid: Control 'lblResult' accessed from a thread other than the thread it was created on.
==<end>==============




==<灰>===========
"Thou shall not access UI controls from a thread other than the one that created the UI control in the first place"
“除了建立UI Control的那條執行緒外，你不可以用其他執行緒去存取該UI Control!”
==<end>==============





==<box>===========
程式3
private void startJob(object path)
{
    fileCount = 0;
    totalSize = 0;
    explore(path.ToString());

    string text = string.Format(
        "{0:#,##0} files, {1:#,##0} bytes",
        fileCount, totalSize);
    //透過Invoke，強制以UI Thread執行
    this.Invoke(
        new UpdateLableHandler(printResult),
        new object[] { text });
}
//宣告一個delegate
delegate void UpdateLableHandler(string text);
//透過Invoke，printReulst會以UI Thread執行
//故可隨意存取UI Control
private void printResult(string text)
{
    lblResult.Text = text;
}==<end>==============



	
==<box>===========
程式4
private void btnGO_Click(object sender, EventArgs e)
{
    if (btnGO.Text == "GO")
    {
        //按鈕功能變更為取消
        btnGO.Text = "Cancel";
        cancel = false;
        ThreadPool.QueueUserWorkItem(
            new WaitCallback(startJob), txtPath.Text);
    }
    else
    {
        //設定取消旗標
        cancel = true;
        //在完全停止前，停用按鈕
        btnGO.Enabled = false;
    }
}
private void startJob(object path)
{
    fileCount = 0;
    totalSize = 0;
    explore(path.ToString());
    string text =
        //取消時顯示”Canceled”，不顯示統計
        (!cancel) ?
            string.Format(
            "{0:#,##0} files, {1:#,##0} bytes",
            fileCount, totalSize) :
            "Canceled";
    this.Invoke(
        new UpdateLableHandler(printResult),
        new object[] { text });
}
delegate void UpdateLableHandler(string text);
private void printResult(string text)
{
    lblResult.Text = text;
    //作業完成，恢復按鈕功能
    btnGO.Text = "GO";
    btnGO.Enabled = true;
}
private void updateProgress(string text)
{
    lblResult.Text = text;
}

private bool cancel = false;

private void explore(string path)
{
    foreach (string dir 
        in Directory.GetDirectories(path))
    {
        //使用者要求中止
        if (cancel) return;
        explore(dir);
    }
    foreach (string file 
        in Directory.GetFiles(path))
    {
        //使用者要求中止
        if (cancel) return;

        //雖然在本例中非必要，但在此還是簡單示範利用
        //Interlocked.Increment增加fileCounter值的做法
        //防止多個Thread同時更動資料時發生衝突
        //另一種做法是用lock(C#)或SyncLock(VB.NET)
        //請參考MSDN獲得更詳細的介紹
        Interlocked.Increment(ref fileCount);

        //每100個檔案回報一下進度
        if (fileCount % 100 == 0)
            this.Invoke(
                new UpdateLableHandler(updateProgress),
                string.Format(
                "{0:#,##0} files processed...",
                fileCount)
            );

        FileInfo fi = new FileInfo(file);
        totalSize += fi.Length;

    }
}==<end>==============





==<box>===========
程式5
private void btnGO_Click(object sender, EventArgs e)
{
    if (btnGO.Text == "GO")
    {
        btnGO.Text = "Cancel";
        fileCount = 0;
        totalSize = 0;
        //啟動非同步呼叫
        backgroundWorker1.RunWorkerAsync(
            txtPath.Text);
    }
    else
    {
        btnGO.Text = "GO";
        btnGO.Enabled = false;
        //取消非同步作業
        backgroundWorker1.CancelAsync();
    }

}

private void explore(string path, BackgroundWorker worker)
{
    foreach (string dir 
        in Directory.GetDirectories(path))
    {
        //以CancellationPending判別是否要取消
        if (worker.CancellationPending) return;
        explore(dir, worker);
    }
    foreach (string file 
        in Directory.GetFiles(path))
    {
        if (worker.CancellationPending) return;
        fileCount++;
        if (fileCount % 100 == 0)
            //利用ReportProgress回報進度
            backgroundWorker1.ReportProgress(
                0, //Progress在此未使用，設0
                string.Format("{0:#,##0} files processed...",
                    fileCount)
            );
                
        FileInfo fi = new FileInfo(file);
        totalSize += fi.Length;
    }
}
//非同步作業
private void backgroundWorker1_DoWork(
    object sender, DoWorkEventArgs e)
{
    //e.Argument接入RunWorkerAsync傳入的參數
    explore((string)e.Argument, 
        sender as BackgroundWorker);
    //執行完成，設執行定結果
    if (backgroundWorker1.CancellationPending)
        e.Cancel = true;
    else
        e.Result = string.Format(
            "{0:#,##0} files, {1:#,##0} bytes",
            fileCount, totalSize);
}
//即時執行進度回報
private void backgroundWorker1_ProgressChanged(
    object sender, ProgressChangedEventArgs e)
{
    lblResult.Text = e.UserState.ToString();
}
//作業完畢處理
private void backgroundWorker1_RunWorkerCompleted(
    object sender, RunWorkerCompletedEventArgs e)
{
    lblResult.Text =
        (e.Cancelled) ?
        "Canceled" : //取消
        e.Result.ToString(); //結果
    //恢復按鈕功能
    btnGO.Text = "GO";
    btnGO.Enabled = true;
}==<end>==============
     



==<box>===========
參考資料
Give Your .NET-based Application a Fast and Responsive UI with Multiple Threads
http://msdn.microsoft.com/msdnmag/issues/03/02/multithreading/ 
==<end>==============