c# - The main form is frozen after finishing copying file (with a progress indicator) using CopyFileEx? -

i have main form, form has button clicking on show copying window progressbar. use thread copying job, after finishing copying (the file copied ok , copying window closed) main form frozen (the controls on form seem not interactive with). task manager shows there not work (0%). there strange here. here code copying dialogue, please see:

public partial class filecopier : form {     [dllimport("kernel32")]     private extern static int copyfileex(string source, string destination, copyprogressroutine copyprogress, int data, ref int cancel, int flags);     private delegate int copyprogressroutine(long totalbytes, long bytescopied, long streamsize, long streamcopied, int streamnumber, int callbackreason, int source, int destination, int data);     public filecopier()     {         initializecomponent();                 }     #region private members     int cancel;     int copyfinished = -1;                     #endregion     #region public methods     public void copy(string source, string destination)     {                     corehandling(source, destination);                 }     public void movefile(string source, string destination)     {         corehandling(source, destination);         if (cancel == 0)//if there no canceling action         {             //delete source file             file.delete(source);         }                 }     #endregion     #region private methods     private void corehandling(string source, string destination)     {         starttime = datetime.now;         threadstart ths = delegate         {             copyfileex(source, destination, updatecopyprogress, 0, ref cancel, 1);         };         new thread(ths).start();         showdialog();         while (copyfinished == -1)         {             thread.sleep(10);         }         copyfinished = -1;     }     private int updatecopyprogress(long totalbytes, long bytescopied, long streamsize, long streamcopied, int streamnumber, int callbackreason, int source, int destination, int data)     {         if (invokerequired)         {                             invoke(new copyprogressroutine(updatecopyprogress), totalbytes, bytescopied, streamsize, streamcopied, streamnumber, callbackreason, source, destination, data);         }         else         {             int percentage = (int)(((double)bytescopied / totalbytes) * 100);             progressbar.position = percentage;             application.doevents();             if (totalbytes == bytescopied || cancel == 1)             {                 dialogresult = dialogresult.ok;                                 }         }                     return 0;     }     #endregion     private void buttoncancel_click(object sender, eventargs e)     {         cancel = 1;     } } 

in code main form, here button click event handler:

private void buttoncopy_click(object sender, eventargs e){     using(filecopier filecopier = new filecopier()){          filecopier.copy("my source file", "my destination file");     } } 

that's all, after finishing copying, method copy() above should exit normally. don't understand what's still doing after finishing copying , makes main form frozen.

your highly appreciated!

copyfinished not modified anywhere , main thread sleeps indefinitely