請教檔案下載範例問題 |
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答題得分者是：william
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cyl
中階會員   發表：163 回覆：171 積分：66 註冊：2002-07-11 發送簡訊給我 |
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william
版主  發表：66 回覆：2535 積分：3048 註冊：2002-07-11 發送簡訊給我 |
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cyl
中階會員 發表：163 回覆：171 積分：66 註冊：2002-07-11 發送簡訊給我 |
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william
版主 發表：66 回覆：2535 積分：3048 註冊：2002-07-11 發送簡訊給我 |
引言:Canvas does not allow drawingIt means the canvas is invalid or it is still under someone else control for drawing. This is usually casued by unsynchronized threads accessing the GUI components. VCL is not thread safe so any update should be performed within the main thread. Refer to the original question. I think the main thread try to invalidate the form/controls while IBindStatusCallback is still working on the controls. To improve the situtation, try: procedure Tmythread.Execute;
var
D:IBindStatusCallback;
begin
FreeOnTerminate := True;
D:=mybind.create;
if URLDownloadToFile(nil,PChar(form1.edit1.text),PChar(form1.edit2.text),0,D)=0 then
ShowMessage(' Download completed successfully : ' form1.edit1.text)
else
ShowMessage('Error during Download ' form1.edit1.text);
Terminate;
end; procedure TForm1.Button1Click(Sender: TObject);
begin
mythread:=Tmythread.Create(false);
if (checkbox1.Checked = true) and (edit3.text<>'') then
timer1.Enabled:=true;
repeat
Application.ProcessMessages;
sleep(10); // add more if needed
until mythread.Terminated or _abort;
end; This is NOT a solution! It just reduces the error rate. BTW, mythread is a global variable and reusing it this way (create a new thread and associate it with mythread every time the button is clicked) may produce unexpected results... |
發表時間：2003-04-22 11:02:11
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