终端服务的剪贴板的缺陷，导致WPF调用Clipboard.SetText() 失败

这是一个在实际项目中遇到的问题，在VPN和远程桌面中，WPF程序对系统剪贴板进行操作的时候，发生CLIPBRD_E_CANT_OPEN异常。从异常本身来看，很明显，是COM有问题。

代码很简单 Clipboard.SetText(mSelection); 但是注意，这个是WPF的窗口，所以调用的是 System.Windows.Clipboard，而不是WinForm的System.Windows.Forms.Clipboard。

经过一番搜索，找到了根源： 

http://stackoverflow.com/questions/68666/clipbrd-e-cant-open-error-when-setting-the-clipboard-from-net

http://blogs.microsoft.co.il/blogs/tamir/archive/2007/10/24/clipboard-setdata-getdata-troubles-with-vpc-and-ts.aspx

原因是微软的Terminal Service 的Clipboard有一个bug，解决方法就是用try-catch包一下函数调用，然后多调用几次，每次之后呢，Sleep一点时间片，代码看上去就是：

for (int i = 0; i < 10; i++)
{
    try
    {
        Clipboard.SetText(str);
        return;
    }
    catch { }
    System.Threading.Thread.Sleep(10);
}

而有人也指出，在.Net 2.0 SP1的时候，微软对Winform的剪切板做了修正，内部就做了这个处理，但是WPF没有！好，那就来看看WinForm和WPF的代码：

WinForm的SetText()最终会调用SetDataObject(data, copy, 10, 100),这个是SetDataObject()的签名：

[UIPermission(SecurityAction.Demand, Clipboard=UIPermissionClipboard.OwnClipboard)]
public static void SetDataObject(object data, bool copy, int retryTimes, int retryDelay)
{
    if (Application.OleRequired() != ApartmentState.STA)
    {
        throw new ThreadStateException(SR.GetString("ThreadMustBeSTA"));
    }
    if (data == null)
    {
        throw new ArgumentNullException("data");
    }
    if (retryTimes < 0)
    {
        object[] args = new object[] { "retryTimes", retryTimes.ToString(CultureInfo.CurrentCulture), 0.ToString(CultureInfo.CurrentCulture) };
        throw new ArgumentOutOfRangeException("retryTimes", SR.GetString("InvalidLowBoundArgumentEx", args));
    }
    if (retryDelay < 0)
    {
        object[] objArray2 = new object[] { "retryDelay", retryDelay.ToString(CultureInfo.CurrentCulture), 0.ToString(CultureInfo.CurrentCulture) };
        throw new ArgumentOutOfRangeException("retryDelay", SR.GetString("InvalidLowBoundArgumentEx", objArray2));
    }
    DataObject obj2 = null;
    if (!(data is IDataObject))
    {
        obj2 = new DataObject(data);
    }
    bool flag = false;
    try
    {
        IntSecurity.ClipboardRead.Demand();
    }
    catch (SecurityException)
    {
        flag = true;
    }
    if (flag)
    {
        if (obj2 == null)
        {
            obj2 = data as DataObject;
        }
        if (!IsFormatValid(obj2))
        {
            throw new SecurityException(SR.GetString("ClipboardSecurityException"));
        }
    }
    if (obj2 != null)
    {
        obj2.RestrictedFormats = flag;
    }
    int num2 = retryTimes;
    IntSecurity.UnmanagedCode.Assert();
    try
    {
        int num;
        do
        {
            if (data is IDataObject)
            {
                num = UnsafeNativeMethods.OleSetClipboard((IDataObject) data);
            }
            else
            {
                num = UnsafeNativeMethods.OleSetClipboard(obj2);
            }
            if (num != 0)
            {
                if (num2 == 0)
                {
                    ThrowIfFailed(num);
                }
                num2--;
                Thread.Sleep(retryDelay);
            }
        }
        while (num != 0);
        if (copy)
        {
            num2 = retryTimes;
            do
            {
                num = UnsafeNativeMethods.OleFlushClipboard();
                if (num != 0)
                {
                    if (num2 == 0)
                    {
                        ThrowIfFailed(num);
                    }
                    num2--;
                    Thread.Sleep(retryDelay);
                }
            }
            while (num != 0);
        }
    }
    finally
    {
        CodeAccessPermission.RevertAssert();
    }
}

 

 

而WPF的SetText()，虽然签名一样，但是具有完全不同的实现：

[SecurityCritical]
public static void SetDataObject(object data, bool copy)
{
    SecurityHelper.DemandAllClipboardPermission();
    CriticalSetDataObject(data, copy);
}

[FriendAccessAllowed, SecurityCritical]
internal static void CriticalSetDataObject(object data, bool copy)
{
    IDataObject obj2;
    if (data == null)
    {
        throw new ArgumentNullException("data");
    }
    if (data is DataObject)
    {
        obj2 = (DataObject) data;
    }
    else if (data is IDataObject)
    {
        SecurityHelper.DemandUnmanagedCode();
        obj2 = (IDataObject) data;
    }
    else
    {
        obj2 = new DataObject(data);
    }
    int num2 = 10;
    while (true)
    {
        int hr = OleServicesContext.CurrentOleServicesContext.OleSetClipboard(obj2);
        if (NativeMethods.Succeeded(hr))
        {
            break;
        }
        if (--num2 == 0)
        {
            Marshal.ThrowExceptionForHR(hr);
        }
        Thread.Sleep(100);
    }
    if (copy)
    {
        Thread.Sleep(10);
        Flush();
    }
}