在迭代之前等待任務完成

Question

我有一個函數，它從目錄讀取每個文件並將其上載到數據庫。 我無法工作，如何等待任務完成它可以追溯到foreach循環之前，因爲它似乎做直線距離，那裏的任務需要幾秒鐘：

foreach (string file in Directory.EnumerateFiles(folderPath, "*.xml")) 
{ 
    //load file 
    currentReader = new XmlDataReader(transferInstructions, file); 

    currentReader.RowsUploaded += new EventHandler<RowsUploadedEventArgs>(currentReader_RowsUploaded); 
    currentReader.TableUploaded += new EventHandler<TableUploadedEventArgs>(currentReader_TableUploaded); 
    currentTask = new Task(() => currentReader.executeBulkCopy(initialConnString, workingDatabase)); 
    currentTask.ContinueWith(task => 
    { 
     cleanUp(task); 
     //MessageBox.Show("Complete!"); 
    }); 
    currentTask.Start(); 
    writeResult("Started the transfer process."); 
    cmdDataTransfer.Text = "CANCEL TRANSFER"; 
    cmdDataTransfer.ForeColor = Color.DarkRed; 
    transferAction =() => cancelCurrentReader(); 
} 

我需要在繼續執行foreach循環之前，請等待MessageBox.show的位置。 清潔（任務）需要幾秒鐘的時間。 //MessageBox.Show("Complete！「）; 部分。

謝謝。

Answer 1

C＃5/.NET 4.5中的async-awqait模式與此完美匹配。我看你已經標記這是.NET4，但如果你能使用Async Targeting Pack，有這樣做的一個非常優雅的方式：

void Main() 
{ 
    foreach (string file in Directory.EnumerateFiles(folderPath, "*.xml")) 
    { 
     currentReader = new XmlDataReader(transferInstructions, file); //load file 
     currentReader.RowsUploaded += new EventHandler<RowsUploadedEventArgs>(currentReader_RowsUploaded); 
     currentReader.TableUploaded += new EventHandler<TableUploadedEventArgs>(currentReader_TableUploaded); 

     var task = Task.Factory.StartNew(() => currentReader.executeBulkCopy(initialConnString, workingDatabase)); 
     await task; 

     cleanUp(task); 
     MessageBox.Show("Complete!"); 
     writeResult("Started the transfer process."); 
     cmdDataTransfer.Text = "CANCEL TRANSFER"; 
     cmdDataTransfer.ForeColor = Color.DarkRed; 
     transferAction =() => cancelCurrentReader(); 
    } 
} 

如果你必須保持VS2010，你將不得不效仿什麼異步等待，沿線的東西：

void MyForm() 
{ 
    _syncContext = SynchronizationContext.Current; 
    Execute(Directory.EnumerateFiles(folderPath, "*.xml").GetEnumerator()); 
} 

void Execute(IEnumerator<string> files) 
{ 
    if (!files.MoveNext()) 
    { 
     files.Dispose(); 
     return; 
    } 
    Task.Factory.StartNew(() => Execute(files.Current)).ContinueWith(() => Execute(files)); 
} 

public void Execute(string file) 
{ 
    currentReader = new XmlDataReader(transferInstructions, file); //load file 
    currentReader.RowsUploaded += new EventHandler<RowsUploadedEventArgs>(currentReader_RowsUploaded); 
    currentReader.TableUploaded += new EventHandler<TableUploadedEventArgs>(currentReader_TableUploaded); 
    () => currentReader.executeBulkCopy(initialConnString, workingDatabase); 
    cleanUp(task); 
    _syncContext.Send(updateGUI); 
    transferAction =() => cancelCurrentReader(); 
} 
public void updateGUI() 
{ 
    MessageBox.Show("Complete!"); 
    writeResult("Started the transfer process."); 
    cmdDataTransfer.Text = "CANCEL TRANSFER"; 
    cmdDataTransfer.ForeColor = Color.DarkRed; 
} 

編輯現在我想到它也有一個更簡單的方法。您可以讓整個循環運行在它自己的任務中（委派到GUI工作的同步上下文）。使用上面的代碼的約定：

Task.Factory.StartNew(() => 
{ 
    foreach (var file in Directory.EnumerateFiles(folderPath, "*.xml")) 
     Execute(file); 
}