Tuesday, November 5, 2019
Submit Forms Using TWebBrowser in Delphi
Populate/Submit Forms Using TWebBrowser in Delphi The TWebBrowser Delphi control provides access to the Web browser functionality from your Delphi apps - to allow you to create a customized Web browsing application or to add Internet, file and network browsing, document viewing, and data downloading capabilities to your applications. Web Forms A web form or a form on a web page allows a web page visitor to enter data that is, in most cases, sent to the server for processing. The simplest web form could consist of one input element (edit control) and a submit button. Most web search engines (like Google) use such a web form to allow you to search the internet. More complex web forms would include drop-down lists, check boxes, radio buttons, etc. A web form is much like a standard windows form with text input and selection controls. Every form would include a button - a submit button - that tells the browser to take action on the web form (typically to send it to a web server for processing). Programmatically Populating Web Forms If in your desktop application you use the TWebBrowser to display web pages, you can programmatically control web forms: manipulate, change, fill, populate fields of a web form and submit it. Heres a collection of custom Delphi functions you can use to list all the web forms on a web page, to retrieve input elements, to programmatically populate fields and to finally submit the form. To more easily follow the examples, lets say theres a TWebBrowser control named WebBrowser1 on a Delphi (standard Windows) form. Note: you should add mshtml to your uses clause in order to compile the methods listed here. List Web Form Names, Get a Web Form by Index A web page would in most cases have only one web form, but some web pages might have more than one web form. Heres how to get the names of all the web forms on a web page: function WebFormNames(const document: IHTMLDocument2): TStringList; var   forms : IHTMLElementCollection;   form : IHTMLFormElement;   idx : integer; begin   forms : document.Forms as IHTMLElementCollection;   result : TStringList.Create;   for idx : 0 to -1 forms.length do   begin     form : forms.item(idx,0) as IHTMLFormElement;     result.Add(form.name) ;   end; end; A simple usage to display the list of web form names in a TMemo: var   forms : TStringList; begin   forms : WebFormNames(WebBrowser1.Document AS IHTMLDocument2) ;   try     memo1.Lines.Assign(forms) ;   finally     forms.Free;   end; end; Heres how to get the instance of a web form by index. For a single form page the index would be 0 (zero). function WebFormGet(const formNumber: integer; const document: IHTMLDocument2): IHTMLFormElement; var   forms : IHTMLElementCollection; begin   forms : document.Forms as IHTMLElementCollection;   result : forms.Item(formNumber,) as IHTMLFormElement end; Once you have the web form, you can list all the HTML input elements by their name, you can get or set the value for each of the fields, and finally, you can submit the web form. Web pages can host web forms with input elements like edit boxes and drop down lists which you can control and manipulate programmatically from Delphi code. Once you have the web form, you can list all the HTML input elements by their name: function WebFormFields(const document: IHTMLDocument2; const formName : string): TStringList; var   form : IHTMLFormElement;   field : IHTMLElement;   fName : string;   idx : integer; begin   form : WebFormGet(0, WebBrowser1.Document AS IHTMLDocument2) ;   result : TStringList.Create;   for idx : 0 to -1 form.length do  begin     field : form.item(idx, ) as IHTMLElement;     if field  nil then Continue;     fName : field.id;     if field.tagName INPUT then fName : (field as IHTMLInputElement).name;     if field.tagName SELECT then fName : (field as IHTMLSelectElement).name;     if field.tagName TEXTAREA then fName : (field as IHTMLTextAreaElement).name;     result.Add(fName) ;   end; end; When you know the names of the fields on a web form, you can programmatically get the value for a single HTML field: function WebFormFieldValue(   const document: IHTMLDocument2;   const formNumber : integer;   const fieldName : string): string; var   form : IHTMLFormElement;   field: IHTMLElement; begin   form : WebFormGet(formNumber, WebBrowser1.Document AS IHTMLDocument2) ;   field : form.Item(fieldName,) as IHTMLElement;   if field  nil then Exit;   if field.tagName INPUT then result : (field as IHTMLInputElement).value;   if field.tagName SELECT then result : (field as IHTMLSelectElement).value;   if field.tagName TEXTAREA then result : (field as IHTMLTextAreaElement).value; end; An example of usage to get the value of an input field named URL: const   FIELDNAME url; var   doc :IHTMLDocument2;   fieldValue : string; begin  doc : WebBrowser1.Document AS IHTMLDocument2;   fieldValue : WebFormFieldValue(doc, 0, FIELDNAME) ;   memo1.Lines.Add(Field : URL, value: fieldValue) ;end; The entire idea would have no value if you would not be able to fill in web form elements: procedure WebFormSetFieldValue(const document: IHTMLDocument2; const formNumber: integer; const fieldName, newValue: string) ; var   form : IHTMLFormElement;   field: IHTMLElement; begin   form : WebFormGet(formNumber, WebBrowser1.Document AS IHTMLDocument2) ;   field : form.Item(fieldName,) as IHTMLElement;   if field  nil then Exit;   if field.tagName INPUT then (field as IHTMLInputElement).value : newValue;   if field.tagName SELECT then (field as IHTMLSelectElement) : newValue;   if field.tagName TEXTAREA then (field as IHTMLTextAreaElement) : newValue; end; Submit a Web Form Finally, when all the fields are manipulated, you would probably want to submit the web form from Delphi code. Heres how: procedure WebFormSubmit(   const document: IHTMLDocument2;   const formNumber: integer) ; var   form : IHTMLFormElement;   field: IHTMLElement; begin   form : WebFormGet(formNumber, WebBrowser1.Document AS IHTMLDocument2) ;   form.submit; end; Not All Web Forms Are Open Minded Some web forms might host a captcha image to prevent web pages from being manipulated programmatically. Some web forms might not be submitted when you click the submit button. Some web forms execute JavaScript or some other procedure gets executed handled by the onsubmit event of the web form. In any event, web pages can be controlled programmatically, the only question is how far are you prepared to go?
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