如何使用 TNetHTTPClient 或 TNetHTTPRequest 从 URL 获取图片并将其放在 TImage 中？

Question

How to get a picture from an URL and put it at TImage using TNetHTTPClient or TNetHTTPRequest? I am beginner and I am using Delphi-10.3-Rio.

I wrote a simple test application, but it does not work as I expect.

I used TNetHTTPClient and TNetHTTPRequest

 object NetHTTPClient: TNetHTTPClient Asynchronous = False ConnectionTimeout = 60000 ResponseTimeout = 60000 HandleRedirects = True AllowCookies = False UserAgent = 'Embarcadero URI Client/1.0' OnAuthEvent = NetHTTPClientAuthEvent Left = 7 Top = 2 end object NetHTTPRqstPicture: TNetHTTPRequest Asynchronous = False ConnectionTimeout = 60000 ResponseTimeout = 60000 MethodString = 'GET' Client = NetHTTPClient OnRequestCompleted = NetHTTPRqstPictureRequestCompleted Left = 103 Top = 5 end

 implementation {$R *.dfm} const cUrlPicture = 'http://192.168.1.3/local/fflprapp/tools.cgi?action=getImage&name=56/20200823171910_718702lp_PA088VI_463274.png'; procedure TForm1.btnGetPictClick(Sender: TObject); begin {0} NetHTTPRqstPicture.Get(cUrlPicture); end; procedure TForm1.NetHTTPClientAuthEvent(const Sender: TObject; AnAuthTarget: TAuthTargetType; const ARealm, AURL: string; var AUserName, APassword: string; var AbortAuth: Boolean; var Persistence: TAuthPersistenceType); begin {0} if AnAuthTarget = TAuthTargetType.Server then begin AUserName:= 'root'; APassword:= 'ACCC8ED325EF'; end; end; procedure TForm1.NetHTTPRqstPictureRequestCompleted(const Sender: TObject; const AResponse: IHTTPResponse); var strm: TStream; pngImg: TPNGImage; begin {0} strm:= TStream.Create; pngImg:= TPNGImage.Create; strm:= AResponse.ContentStream; pngImg.LoadFromStream(strm); imgPict.Picture.Graphic:= pngImg; FreeAndNil(pngImg); // OK always FreeAndNil(strm); // Here is something strange. end; end.

--- here is how executes FreeAndNil(strm) ---

1st click on btnGetPict - everything is OK

2nd click on btnGetPict - apear a message: Access violation at address 00407F74 in module 'ProjGetPicture.exe'. Read of address FFFFFFFD.

3rd click on btnGetPict - everything is OK

4th click on btnGetPict - apears a same message again and so on.

I do not know why.

If I delete FreeAndNil(strm); Everything is OK, but it is a leakage memory.

If I modify a code like this

var strmG: TStream; procedure TForm1.FormCreate(Sender: TObject); begin strmG:= TStream.Create; end; procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction); begin FreeAndNil(strmG); end; // and use strmG instead strm in: // strmG:= AResponse.ContentStream; // pngImg.LoadFromStream(strmG);

Everything is run.... until the program closes, when apear same message.

Answer 1

Insert the following code into the btnGetPict button's click handler

procedure TForm1.btnGetPictClick(Sender: TObject); var Memo: TMemoryStream; png: TPngImage; begin Memo:= TMemoryStream.Create; try NetHTTPClient1.Get(cUrlPicture, Memo); // cUrlPicture - this you constant with url from an picture Memo.Position:= 0; png:= TPngImage.Create; try png.LoadFromStream(Memo); Image1.Picture.Assign(png); finally png.Free; end; finally Memo.free; end; end;

Also, don't forget to add the name of the PNGImage library to the uses line. If you want to load a jpeg file, plug in the JPEG library. Insert the code below.

 procedure TForm1.Button9Click(Sender: TObject); var Memo: TMemoryStream; jpg:TJPEGImage; begin Memo:= TMemoryStream.Create; try NetHTTPClient1.Get(cUrlPicture, Memo); Memo.Position:= 0; jpg:= TJPEGImage.Create; try jpg.LoadFromStream(Memo); Image1.Picture.Assign(jpg); finally. jpg.Free; end; finally. Memo.free; end; end;