祝所有 StackOverFlow 会员和读者新年快乐！
我今天来找你询问有关 Delphi 中线程的问题（我浏览了大部分已经发布的关于该主题的内容，但找不到线索）。
我有一个非常简单的测试应用程序，其中包含一个表单（frmIMGDown）和一个线程单元。
表格上可以找到
单击时，该按钮会启动一个线程，从网络下载图像，在此过程中更新进度条并在 Timage 中显示下载的图像。
只要调用表单 (frmIMGDown) 是主申请表单，就可以正常工作，或者如果从另一种形式调用它但是所有表格均在应用程序启动时创建.
现在，如果我通过按钮动态创建 frmIMGDown，请单击主窗体：
procedure TForm1.Button2Click(Sender: TObject);
var
frmIMGDown : TfrmIMGDown;
begin
try
frmIMGDown := TfrmIMGDown.Create(nil);
frmIMGDown.ShowModal;
finally
frmIMGDown.Free;
end;
end;
我得到一个地址访问冲突... error
如果我改变
frmIMGDown := TfrmIMGDown.Create(nil);
to
frmIMGDown := TfrmIMGDown.Create(Form1);
结果是相同的，但有相同的错误。
我怀疑这与我实现的线程以及可能使用的变量有关，并且我尝试发送回 frmIMGDown，但我找不到解决方案。
这是线程单元：
unit unit_MyThread;
interface
uses
Classes, IdHTTP, VCL.Forms, SyStem.UITypes, SysUtils, VCL.Dialogs, Graphics, IdTCPClient, IdTCPConnection, IdComponent,IdBaseComponent;
type
TIdHTTPThread = class(TThread)
private
FURL : String;
idHTTP: TIdHTTP;
B : TBitMap;
W : TWICImage;
//MS : TMemoryStream;
public
Constructor Create(CreateSuspended: Boolean);
Destructor Destroy; override;
Property URL : String read FURL WRITE FURL;
procedure OnWork(ASender: TObject; AWorkMode: TWorkMode; AWorkCount: Int64);
procedure OnWorkBegin(ASender: TObject; AWorkMode: TWorkMode; AWorkCountMax: Int64);
procedure OnWorkEnd(ASender: TObject; AWorkMode: TWorkMode);
protected
procedure Execute; override;
end;
implementation
uses
unit_IMG_Down;
Constructor TiDHTTPThread.Create(CreateSuspended: Boolean);
begin
inherited Create(Suspended);
IdHTTP := TIdHTTP.Create;
Screen.Cursor := crHourGlass;
IdHTTP.onWork := OnWork;
IdHTTP.OnWorkbegin := OnWorkBegin;
IdHTTP.OnWorkEnd := OnWorkEnd;
B := TBitmap.Create;
W := TWICImage.Create;
end;
Destructor TIdHTTPThread.Destroy;
begin
idHTTP.Free;
B.Free;
W.Free;
Screen.Cursor := crDefault;
inherited Destroy;
end;
procedure TIdHTTPThread.Execute;
var
MS : TMemoryStream;
begin
Screen.Cursor := crHourGlass;
try
MS := TMemoryStream.Create;
try
IdHTTP.Request.UserAgent := 'Mozilla/5.0 (Windows NT 6.1; WOW64; rv:12.0) Gecko/20100101 Firefox/12.0';
IdHTTP.Get(URL,MS);
MS.Position := 0;
W.LoadFromStream(MS);
B.Assign(W);
frmIMGDown.Image3.Picture.Assign(B);
except
On E: Exception do ShowMessage(E.Message);
end;
finally
MS.Free;
end;
end;
procedure TIdHTTPThread.OnWork(ASender: TObject; AWorkMode: TWorkMode;
AWorkCount: Int64);
var
Http: TIdHTTP;
ContentLength: Int64;
Percent: Integer;
begin
Http := TIdHTTP(ASender);
ContentLength := Http.Response.ContentLength;
if (Pos('chunked', LowerCase(Http.Response.TransferEncoding)) = 0) and
(ContentLength > 0) then
begin
Percent := 100*AWorkCount div ContentLength;
frmIMGDown.ProgressBar3.Position := AWorkCount +2;
frmIMGDown.ProgressBar3.Position := AWorkCount -1;
end;
end;
procedure TIdHTTPThread.OnWorkBegin(ASender: TObject; AWorkMode: TWorkMode;
AWorkCountMax: Int64);
begin
frmIMGDown.ProgressBar3.Visible := True;
frmIMGDown.ProgressBar3.Position := 0;
end;
procedure TIdHTTPThread.OnWorkEnd(ASender: TObject; AWorkMode: TWorkMode);
begin
frmIMGDown.ProgressBar3.Visible := false;
end;
end.
以及从按钮调用线程
procedure TfrmIMGDown.Button3Click(Sender: TObject);
var
HTTPThread : TIdHTTPThread;
begin
HTTPThread := TIdHTTPThread.Create(False);
HTTPThread.URL := 'https://bw-1651cf0d2f737d7adeab84d339dbabd3-bcs.s3.amazonaws.com/products/product_119522/Full119522_283b3acc91f119ab4b2939b1beb67211.jpg';
HTTPThread.FreeOnTerminate := True;
end;
旁注：我使用 TWICImage 下载图像（LoadFromStream），因为我不知道图像将采用哪种格式（这里 URl 是硬编码用于测试），然后将其分配给 TBitmap。
提前致谢，再次祝大家新年快乐。
Math
