Invoke问题,大家帮我看看啊

Question

整个代码大概是这样的:
public abstract class ParentForm:System.Windows.Forms.Form{
   ...
   public abstract bool Open();
}public class ChildForm: ParentForm {
  public override bool Open(){
    ...
    this.DocumentOpen(doc,printLayouts);
  }  public bool DocumentOpen(XmlDocument doc, DesignerLinkedPrintLayout[] printLayouts) {
              if (doc != null) {
   this.SetStatus("Reading Information...");
   this.Progress = (int)Math.Ceiling(100 / 7.0F * 1.0F);    Hashtable hash = new Hashtable();    hash.Add(doc, printLayouts);
                     ThreadPool.QueueUserWorkItem(new System.Threading.WaitCallback(this.documentOpen), hash);
              }
              return true;
 } private void documentOpen(object obj) {
     ...
     this.Invoke(new EmptyParamDelegate(this.documentOpen));
 } private void documentOpen(){
   ...
 }}public class TestForm :System.Windows.Forms.Form{
  ...
  private void btnOpen_Click(object sender, EventArgs e){
    ParentForm frm = this.CreateForm();//这里得到的是一个ChildForm instance
    if(frm.Open()){
       this.ShowFrom(frm);
    }elss{
       frm.Dispose();  
    }
  } 
}现在有一个问题就是:
当我打开ChildForm然后关闭,再次就无法打开,老是提示System.ObjectDisposedException
错误如下:
Exception: System.ObjectDisposedException
Message: Cannot access a disposed object.
Object name: 'ChildForm'.
Source: System.Windows.Forms
   at System.Windows.Forms.Control.MarshaledInvoke(Control caller, Delegate method, Object[] args, Boolean synchronous)
   at System.Windows.Forms.Control.Invoke(Delegate method, Object[] args)
   at System.Windows.Forms.Control.Invoke(Delegate method)
   at FLogic.Workflow.Designer.WorkflowDesigner.WorkflowDesignerWorkForm.documentOpen(Object obj) in C:\Projects\ChildForm.cs:
   at System.Threading._ThreadPoolWaitCallback.WaitCallback_Context(Object state)
   at System.Threading.ExecutionContext.runTryCode(Object userData)
   at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading._ThreadPoolWaitCallback.PerformWaitCallbackInternal(_ThreadPoolWaitCallback tpWaitCallBack)
   at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback(Object state)
大家帮我找找是什么原因啊
每次指示的是  this.Invoke(new EmptyParamDelegate(this.documentOpen));这行出错.

Answer 1

而且在visual studio 2008中选择附加到进程,调试的时候是多次打开这个Form是没问题的.

Answer 2

不要用局部变量,可能这个委托被垃圾回收了.EmptyParamDelegate ep=new EmptyParamDelegate(this.documentOpen));
private void documentOpen(object obj) {
  ...
  this.Invoke(ep);
 }