How to Create at Runtime Winforms

Question

Hello to all: We always have developing with delphi 5 and now we are trying to start to develop with Visual C# .Net Does any one know how can I from the principal winform create other winforms at runtime? and how to prevent when the user click over the button create another instance of the second winform in other words if the second winform is already created only restore the second form and bring to front but if the second form is not created yet create the second form this will posible. This is because in delphi 5 we resolving this problem with the next code: var frm : TSecondForm; ... frm := TSecondForm(Application.MainForm.FindComponent('SecondForm')); if frm = nil then begin frm := TSecondForm.Create(Application.MainForm); frm.Show; end else begin frm.WindowState := wsNormal; frm.BringToFront; end; Is this posible?  please can you provide a complete example or where can I learn more about this issues. Best Regards.

spgilmore · Answer

This may not be the best way but it's the only way I know of. Objects that you create do not set all references to NULL when they're destroyed because they may not be destroyed when you expect them. They're only destroyed when the garbage collector gets to it. Instead you have to watch for their disposal which is what puts them on the garbage collector's to-do-list. Add a listener to the form by adding a function to the Form2.Disposed delegate. In Visual Studio it does everything for you by prompting you to press TAB. if (frm == null) { frm = new Form2(); frm.Disposed +=new ... <press CTRL-J here and it will prompt you... } When you get the prompt press TAB and it will finishe the line. Press it again and it will create the System.Event for you. It will look like this in the end: private Form2 frm; private void button5_Click(object sender System.EventArgs e) { if (frm == null) { frm = new Form2(); frm.Disposed +=new EventHandler(frm_Disposed); } frm.Visible = true; frm.BringToFront(); frm.Show(); } private void frm_Disposed(object sender EventArgs e) { frm = null; }

misael7719 · Answer

Helo SPGILMORE. Thank you very much for your help. I have test your code and when I create at first time the second winform and try to create again the second form the this bring to front great but when a Close the second form and try again to create the program cause an exception. Best Regards.

spgilmore · Answer

You can simply create an instance of the form class just as you did in the Delphi code. private Form2 frm; private void button1_Click(object sender System.EventArgs e) { if (frm == null) { frm = new Form2(); } frm.Visible = true; frm.BringToFront(); frm.Show(); }