 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
.NET Forum / Windows Forms / WinForm General / January 2008Passing an object back to a form
I am developing an application in VS2005, using VB.NET. Suppose that I have a class, called Widget, which contains, among other things, a List(Of WidgetDetail), where WidgetDetail is another class. Now, let's say that I have a Widget form, called WidgetForm, and that it is used to enter Widgets. This form currently has a private module- level variable, called m_oCurrentWidget which is an instance of Widget. On WidgetForm, there is a button to add a new WidgetDetail to be associated with the Widget being worked on currently on WidgetForm. When the user clicks on this button, another form, called WidgetDetailForm, is shown that is used to enter information for a WidgetDetail. The WidgetDetailForm form currently has a private module- level variable, called m_oCurrentWidgetDetail, which is an instance of WidgetDetail. Well, what I want to do when the user clicks on the button, on the WidgetDetailForm form, to confirm addition of the WidgetDetail, is to add the WidgetDetail object defined on WidgetDetailForm, to m_oCurrentWidget's WidgetDetailList (e.g. m_oCurrentWidget.WidgetDetailList.Add(m_oCurrentWidgetDetail)). Given that m_oCurrentWidget and m_oCurrentWidgetDetail are on two different forms, what is the best way to implement something like this? The more general question is, what's the best way to pass back an Object from a form on which it is created? > The more general question is, what's the best way to pass back an > Object from a form on which it is created? You could do something like add a readonly property to the child form of type WidgetDetail called something like SelectedWidget, and then after calling ChildForm.Show() just pull out the object from the property: Dim ChildForm as New WidgetForm() ChildForm.Show(true) m_oCurrentWidget.Add(ChildForm.SelectedWidget) Thanks Leon... I was thinking something like that. However, what confuses me is that I am attempting to reference the readonly property of ChildForm AFTER it has been shown (i.e. AFTER it has CLOSED). How is it that I'm able to reference that property after the ChildForm is closed? Is it still in memory? If yes, when does it go away? I should have mentioned that I will be be doing ChildForm.ShowDialog rather than ChildForm.Show. >I should have mentioned that I will be be doing ChildForm.ShowDialog > rather than ChildForm.Show. Remember that when showing a form you are just calling a method on a class you have instantiated, consider the code I posted before (edited to use ShowDialog): Dim ChildForm as New WidgetForm() ChildForm.ShowDialog() m_oCurrentWidget.Add(ChildForm.SelectedWidget) The ChildForm object has not gone out of scope or otherwise been destroyed, its visibility has nothing to do with its existence (except as far as the user is concerned). > The ChildForm object has not gone out of scope or otherwise been destroyed, > its visibility has nothing to do with its existence (except as far as the > user is concerned). Good point. For some reason I thought that when a form "closed", it "went away". That was silly of me. So, if I wanted to be all neat and tidy about things, I could add a line ChildForm = Nothing to facilitate freeing the memory (without just waiting for garbage collection to do it), I suppose. I would, of course, do this after pulling any information I need from ChildForm. Thanks... >> The ChildForm object has not gone out of scope or otherwise been destroyed, >> its visibility has nothing to do with its existence (except as far as the [quoted text clipped - 11 lines] > >Thanks... Setting the reference to Nothing does not cause the object to be disposed. Only calling the object's Dispose method does that. If the ChildForm variable has scope beyond the current method, then setting it to Nothing will make the object available for garbage collection sooner. I disagree with this approach. A cleaner approach would be to add a public property to the parent form, and set it in the child form (to which you would pass a reference to the parent form). It's best not to check properties in the child form after you've closed it. An even cleaner approach would be to have the parent call a method in the child form that returns what you want, and have the child form show itself and return the list, like this: In the child: Private newWidget as oWidget = Nothing Public Function GetWidget() As oWidget Me.ShowDialog() If (Me.DialogResult = Windows.Forms.DialogResult.OK) Then _ Return newWidget Else Return Nothing End If End Function Private Function SaveStuff() 'validate? this would run when the user hits OK Me.DialogResult = Windows.Forms.DialogResult.OK End Function In the parent: Dim getWidget as oWidget getWidget = (New childForm).GetWidget 'this will show the childForm If (getWidget Is Nothing) 'they cancelled Else 'add it to your list End IF RobinS. --------------------------------- >> The more general question is, what's the best way to pass back an >> Object from a form on which it is created? [quoted text clipped - 6 lines] > ChildForm.Show(true) > m_oCurrentWidget.Add(ChildForm.SelectedWidget) > An even cleaner approach would be to have the parent call a method in the > child form that returns what you want, and have the child form show itself [quoted text clipped - 32 lines] > 'add it to your list > End IF That's not really much different than the solution I posted, apart from (as you stated correctly) checking the form status which I left out, as you would have to set this in your OK and Cancel button's event handlers on the child form. > I disagree with this approach. A cleaner approach would be to add a public > property to the parent form, and set it in the child form (to which you [quoted text clipped - 52 lines] > > - Show quoted text - I agree and any other object could call it as well without hardcoding the child to work with one form. Plus making a reference call to a memory released object just is bad in theory and makes the your code read harder. > Plus making a reference call to a > memory released object just is bad in theory and makes the your code > read harder. The class will not have been released from memory after .ShowDialog() has been called.
Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
|
Reply to this Message
|
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.