c# - 包含类型不实现接口(interface) IMessageFilter

Question

我仍在尝试找出此错误的原因:

OCR.test.IMessageFilter.PreFilterMessage(ref System.Windows.Forms.Message): containing type does not implement interface System.Windows.Forms.IMessageFilter

这是我的代码:

bool IMessageFilter.PreFilterMessage(ref Message m) // Error with this line
{
    TwainCommand cmd = tw.PassMessage(ref m);
    if (cmd == TwainCommand.Not)
        return false;

    switch (cmd)
    {
        case TwainCommand.CloseRequest:
        {
            EndingScan();
            tw.CloseSrc();
            break;
        }
        case TwainCommand.CloseOk:
        {
            EndingScan();
            tw.CloseSrc();
            break;
        }
        case TwainCommand.DeviceEvent:
        {
           break;
        }
        case TwainCommand.TransferReady:
        {
            ArrayList pics = tw.TransferPictures();
            EndingScan();
            tw.CloseSrc();
            picnumber++;
            for (int i = 0; i < pics.Count; i++)
            {
                IntPtr img = (IntPtr)pics[i];
                PicForm newpic = new PicForm(img);
                newpic.MdiParent = this;
                int picnum = i + 1;
                //newpic.Text = "ScanPass " + picnumber.ToString() + "_Pic " + picnum.ToString();
                newpic.Show();
            }
            break;
        }
    }

    return true;
}

Answer 1

实现 PreFilterMessage 方法的类需要派生自 IMessageFilter 接口(interface)。你可能错过了

public class Foo: IMessageFilter
{
   bool IMessageFilter.PreFilterMessage(ref Message m)
   {
       // your code
   }
}