BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  strange exception while creating controls          BorlandTalk.com Forum Index -> C++ Builder (VCL Components Usage) View previous topic :: View next topic   Author Message JD Guest Posted: Sat Nov 29, 2003 12:12 pm    Post subject: Re: strange exception while creating controls Maciej Komosinski <Maciej.Komosinski (AT) cs (DOT) put.poznan.pl> wrote: Quote: [...] What is strange is that I discovered that there is no exception when I hide the whole form first, then add TListViews and TSplitters, and then show the form again! Everything looks well then. My experiance is that when I have encountered this same sort of weird behavior, its always been caused by impropper memory management elsewhere in my code. For example, using delete v/s delete [] or vice versa or writting past the end of an allocated block or inadvertantly dereferencing a pointer. HTH ~ JD Back to top Maciej Komosinski Guest Posted: Sat Nov 29, 2003 12:24 pm    Post subject: strange exception while creating controls Hello, Please tell me what may be a reason for the exception EComponentError: "A component named _1 already exists"? My GUI is rather complicated, I have a TForm with a TFrame inside, and many TListViews and TSplitters in the TFrame. This exception occurs while adding TListViews and TSplitters to the TFrame (always in the same moment, when adding the third TListView and the second TSplitter). I created another simple test application and checked that there is no such exception in my simple test program which uses similar approach. The exception occurs only in my complex GUI. What is strange is that I discovered that there is no exception when I hide the whole form first, then add TListViews and TSplitters, and then show the form again! Everything looks well then. The reasons for this exception are very difficult to discover for me. I am using BCB5, and CodeGuard did not discover any problems. Please tell me, what are generally causes for this kind of exception? (EComponentError: "A component named _1 already exists")? Why there is "_1"? This may be some clue for me... Thank you, Maciej Back to top Maciej Komosinski Guest Posted: Sat Nov 29, 2003 10:50 pm    Post subject: Re: strange exception while creating controls Quote: [...] What is strange is that I discovered that there is no exception when I hide the whole form first, then add TListViews and TSplitters, and then show the form again! Everything looks well then. My experiance is that when I have encountered this same sort of weird behavior, its always been caused by impropper memory management elsewhere in my code. For example, using delete v/s delete [] or vice versa or writting past the end of an allocated block or inadvertantly dereferencing a pointer. I use CodeGuard, and anyway I am sure the code is OK, because the non-GUI part has been tested thoroughly for a few years. I noticed that when I add the third TListView, everything is fine until it is made Visible. In that moment I always get this exception. If it is visible from the beginning, then the exception occurs the first time it is modified somehow (like ShowColumnHeaders is modified etc.) When the third TListView is made visible, the stack looks like myAddListView TControl:SetVisible TCustomListView:WndProc TWinControl:UpdateControlState TWinControl:CreateHandle TCustomListView:CreateWnd TStream:ReadComponent TReader:ReadRootComponent TComponent:SetName TComponent:ValidateRename EComponentError: "A component named _1 already exists" is the TStream calls usual for just creating controls by using listview=new TListView(this)? Maybe somebody who knows VCL internals can tell when such an exception may occur? Thank you, Maciej Back to top Fishface Guest Posted: Sun Nov 30, 2003 5:08 am    Post subject: Re: strange exception while creating controls Maciej Komosinski wrote: Quote: I created another simple test application and checked that there is no such exception in my simple test program which uses similar approach. The exception occurs only in my complex GUI. Have you stepped through your code in the debugger? You can debug right into the VCL source and find-out exactly what is causing it. The only time I have received a similar error is when I tried dynamically creating multiple instances of a TFrame descendant. They are somehow born with a non-unique name (at least in BCB5), unlike a regular component. When added to the form's component list, it throws the exception. I don't suppose you are doing anything like that? The VCL wants each component of a of a given control to have a unique name, or no name. When you add a control to your frame or form, is it streamed or otherwise duplicated from and existing control and as such have a name? Back to top Fishface Guest Posted: Sun Nov 30, 2003 7:40 am    Post subject: Re: strange exception while creating controls Maciej Komosinski wrote: Quote: I use CodeGuard, and anyway I am sure the code is OK, because the non-GUI part has been tested thoroughly for a few years. Codeguard will let you get away with a multitude of VCL sins if you build with runtime packages and don't use debug libraries Quote: I noticed that when I add the third TListView, everything is fine until it is made Visible. In that moment I always get this exception. If it is visible from the beginning, then the exception occurs the first time it is modified somehow (like ShowColumnHeaders is modified etc.) When the third TListView is made visible, the stack looks like myAddListView TControl:SetVisible TCustomListView:WndProc TWinControl:UpdateControlState TWinControl:CreateHandle TCustomListView:CreateWnd TStream:ReadComponent TReader:ReadRootComponent TComponent:SetName TComponent:ValidateRename EComponentError: "A component named _1 already exists" is the TStream calls usual for just creating controls by using listview=new TListView(this)? The call stack looks like the result of a call to RecreateWnd() of either the form or the frame, not simply creating a component Before your call to create the TListView, try dumping the component list to a file and looking for something with a name. TMemoryStream *stream1, *stream2; stream1 = new TMemoryStream; stream2 = new TMemoryStream; stream1->WriteComponent(this); stream1->Position = 0; ObjectBinaryToText(stream1, stream2); delete stream1; stream2->SaveToFile("C:\dump.txt"); delete stream2; I see you are making the form the Owner of the TListView. It's not going on the frame, is it? Are you creating anything dynamically in the frame's code and assigning the form as the owner? If you are, and it is created when you drop one on the at design time, it will be streamed with the form as part of the components array. I don't know how it would get the name, though. I'm just grasping at this point... I could see a third *frame* causing an exception. If you kept the default names, the frame would be given a name of TFrame1. The first would have to be put on the form at design time and the designer would name it TFrame11. At runtime, if you create another, it would have the name Frame1. A third would again have a name of Frame1, which already exists and throws the exception. It's a bug in BCB5, and I doubt very much if they fixed it, since they didn't fix much else. Back to top Maciej Komosinski Guest Posted: Sun Nov 30, 2003 9:17 pm    Post subject: Re: strange exception while creating controls Quote: I use CodeGuard, and anyway I am sure the code is OK, because the non-GUI part has been tested thoroughly for a few years. Codeguard will let you get away with a multitude of VCL sins if you build with runtime packages and don't use debug libraries That's how I do. Quote: ... TReader:ReadRootComponent TComponent:SetName TComponent:ValidateRename EComponentError: "A component named _1 already exists" is the TStream calls usual for just creating controls by using listview=new TListView(this)? The call stack looks like the result of a call to RecreateWnd() of either the form or the frame, not simply creating a component Before your call to create the TListView, try dumping the component list to a file and looking for something with a name. ... stream2->SaveToFile("C:\dump.txt"); delete stream2; I see you are making the form the Owner of the TListView. It's not going on the frame, is it? Are you creating anything dynamically in the frame's code and assigning the form as the owner? I create *everything* in runtime. TForm is a parent and owner of some buttons and a single frame. The TFrame is a parent and owner of some TListViews and TSplitters. Adding more than two TListViews to the TFrame causes the exception. Here is the dump of the TFrame children: After the first TListView is added: object TFrame ... object TListView end end After the second one: object TFrame ... TabOrder = 0 object _1: TListView <-- what's this _1 ?? ... ViewStyle = vsReport end object TListView <-- ...and why there is no _something here? ... ViewStyle = vsReport end end ....and the exception will happen soon! So I expect the problem is with components Names. I used listview->Name=somethingunique; to make names of each TListView unique and it works: object TFrame object TSplitter object TSplitter object TSplitter object xx0: TListView object xx1: TListView object xx2: TListView object xx3: TListView end Thank you very much for helping me with this problem. I did not know I had to manually assign names. In the documentation, borland says: TControl::Name Warning: Change control names only at design time. so actually I should not directly modify names. The other thing which is strange for me is that TSplitters don't have names and TListView's have... Yours, Maciej Back to top Fishface Guest Posted: Mon Dec 01, 2003 2:52 am    Post subject: Re: strange exception while creating controls Maciej Komosinski wrote: Fishface wrote: Quote: Codeguard will let you get away with a multitude of VCL sins if you build with runtime packages and don't use debug libraries That's how I do. Here's a link: http://groups.google.com/groups?selm=3e77667b%40newsgroups.borland.com It gives you a false sense of security if it's not set-up just right. Quote: I did not know I had to manually assign names. I have never had to do this, and I tried all kinds of things like creating several TListViews on form and a frame, and I did not find any names being mysteriously assigned to the TListViews. I'm baffled. Are you streaming properties, or a form layout? Somehow, it's getting that name! Back to top Maciej Komosinski Guest Posted: Mon Dec 01, 2003 12:13 pm    Post subject: Re: strange exception while creating controls Quote: I did not know I had to manually assign names. I have never had to do this, and I tried all kinds of things like creating several TListViews on form and a frame, and I did not find any names being mysteriously assigned to the TListViews. I'm baffled. Are you streaming properties, or a form layout? Somehow, it's getting that name! I am not streaming anything... just creating everything in run-time, using new. What is strange is that the exception DID NOT occur in my test application, where I had TForm and TFrame created as resources, and I only added TListViews and TSplitters to the TFrame. This made me think the problem is elsewhere, not in adding subsequent TListViews. BTW, I learned that I do not need to create unique Names for TListViews, I just set all their Names to "". 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