C＃WinForms：識別拖放操作事件的類型

Question

用例：用戶需要將我的WinForms（.Net 4）應用程序中從Outlook拖放電子郵件項目到表單中的能力。應用程序以.msg格式保存這些項目並將它們存儲在預定位置。

問題：我的代碼對於從其他來源的拖放（例如，將IE中的jpeg拖到表單上觸發相同的事件）不夠穩健。這是因爲我無法確定拖動的項目是否是Outlook對象，或拖動的項目來自哪個源。

是否有解決方法，我只能接受特定類型的拖放項目？這是我在DragDrop事件處理代碼：

Outlook.Application outlook = new Outlook.Application(); 
Outlook.Selection sel = outlook.ActiveExplorer().Selection; 

try 
{  
    foreach (object item in sel) 
    { 
     if (item is Outlook.MailItem) 
     { 
      var mail = item as Outlook.MailItem; 

      CopyMailItemToLocalTempDir(mail); 

      txtComment.Text = "Email from " + mail.SenderName + " Regarding " + mail.Subject; 
     } 
    } 
} 
finally 
{ 
    // This is hokey but it prevents Outlook from remembering previously selected items 
    // - refer http://stackoverflow.com/questions/14090420/interop-outlook-doesnt-clear-selected-mails-at-drag-and-drop 
    var folder = outlook.ActiveExplorer().CurrentFolder; 
    outlook.ActiveExplorer().CurrentFolder = outlook.GetNamespace("MAPI").GetDefaultFolder(Outlook.OlDefaultFolders.olFolderContacts); 
    Thread.Sleep(50); 
    outlook.ActiveExplorer().CurrentFolder = folder; 

    Marshal.ReleaseComObject(sel); 
    Marshal.ReleaseComObject(outlook); 
    sel = null; 
    outlook = null; 
} 

從Outlook拖動時DragEventArgs對象（e）就一些細節：

e.Data.GetFormats() returns: 
{string[15]} 
    [0]: "RenPrivateSourceFolder" 
    [1]: "RenPrivateLatestMessages" 
    [2]: "RenPrivateMessages" 
    [3]: "RenPrivateItem" 
    [4]: "FileGroupDescriptor" 
    [5]: "FileGroupDescriptorW" 
    [6]: "FileDrop" 
    [7]: "FileNameW" 
    [8]: "FileName" 
    [9]: "FileContents" 
    [10]: "Object Descriptor" 
    [11]: "System.String" 
    [12]: "UnicodeText" 
    [13]: "Text" 
    [14]: "CSV" 

e.Data.GetData("Text") returns: 
"From\tSubject\tReceived\tSize\tCategories\t\r\nJoe Sender\tThis is the email subject\t10:51 AM\t3 KB\t\t" 

Answer 1

我這裏有解決方案的源代碼，允許只放棄前景項目。這裏是事件處理程序：

private void Form1_DragEnter(object sender, DragEventArgs e) 
    { 
     //display formats available 
     this.label1.Text = "Formats:\n"; 
     foreach (string format in e.Data.GetFormats()) 
     { 
      this.label1.Text += " " + format + "\n"; 
     } 

     //ensure FileGroupDescriptor is present before allowing drop 
     if (e.Data.GetDataPresent("FileGroupDescriptor")) 
     { 
      e.Effect = DragDropEffects.All; 
     } 
    } 

    private void Form1_DragDrop(object sender, DragEventArgs e) 
    { 
     //wrap standard IDataObject in OutlookDataObject 
     OutlookDataObject dataObject = new OutlookDataObject(e.Data); 

     //get the names and data streams of the files dropped 
     string[] filenames = (string[])dataObject.GetData("FileGroupDescriptorW"); 
     MemoryStream[] filestreams = (MemoryStream[])dataObject.GetData("FileContents"); 

     this.label1.Text += "Files:\n"; 
     for (int fileIndex = 0; fileIndex < filenames.Length; fileIndex++) 
     { 
      //use the fileindex to get the name and data stream 
      string filename = filenames[fileIndex]; 
      MemoryStream filestream = filestreams[fileIndex]; 
      this.label1.Text += " " + filename + "\n"; 

      //save the file stream using its name to the application path 
      FileStream outputStream = File.Create(filename); 
      filestream.WriteTo(outputStream); 
      outputStream.Close(); 
     } 
    }