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.NET Forum / .NET Framework / Compact Framework / December 2007do we need to dispose screen controls?
hi there, i use vs2005, c# and .netcf2. i know that i have to explicitly dispose any controls and components which created by myself. but how about those controls, e.g. button, which drew by c# on the screen. as a good practice, should i dispose them explicitly? or c# already does it for me with the system generated code? where is the code? i know they will be handled eventually by GC but it does not guaranteed. thanks batterhead If they are part of the Controls collection in a Form, then the Form will dispose of them for you.  SignatureChris Tacke, eMVP Join the Embedded Developer Community http://community.opennetcf.com > hi there, > [quoted text clipped - 9 lines] > thanks > batterhead Just ensure you call dispose on your form. It is good practice to use the using statement. ie: in C#: using (MyForm form = new MyForm()) { form.ShowDialog(); } When control leaves the above block, the CLR will call Dispose on that form. When creating a form via the Wizard, it will override the Dispose method of the Component class and call Dispose on this for you. It overrides to clean up the components object and so you can place stuff in there if you want. You can find this in the designer partial class. ie MyForm.designer.cs. SignatureSimon Hart Visual Developer - Device Application Development MVP http://simonrhart.blogspot.com > hi there, > [quoted text clipped - 9 lines] > thanks > batterhead Simon Hart wrote: > Just ensure you call dispose on your form. It is good practice to use the > using statement. ie: in C#: [quoted text clipped - 3 lines] > form.ShowDialog(); > } This doesn't compile, at least for me anyway (VS2003) using (Form form = new Form ()) {} Also, "(new Form () is IDisposable)" is false. What am I doing wrong? Hilton IIRC, The using keyword isn't available until CF 2.0 (Studio '05). SignatureChris Tacke, eMVP Join the Embedded Developer Community http://community.opennetcf.com > Simon Hart wrote: >> Just ensure you call dispose on your form. It is good practice to use the [quoted text clipped - 15 lines] > > Hilton Chris, "using" is definitely a 1.0 keyword. I use it all the time; e.g. "using (StreamReader sr = new StreamReader (...))". The problem is that Form does not implement IDisposable on CF 1. Now if Form all of a sudden does implement IDisposable, then that is, by Microsoft's definition, "a breaking change" and should not be done. "(new Form () is IDisposable) return false on CF 1.0, but true on .NET (desktop). Interesting... Seems like a major screwup/oversight by Microsoft. Yes? That's why I still think that the GC should have: "if o implements IDisposable && (!o.Disposed) then o.Dispose" (pseudo code). But I was shot down last time and I guess I will be again. So, Form does not implement IDisposable on the Compact Framework - solve that. If it is in CF 2.0, that is a breaking change and should not be done (according to Microsoft). Comments? Hilton > IIRC, The using keyword isn't available until CF 2.0 (Studio '05). > [quoted text clipped - 18 lines] >> >> Hilton I just checked CF 1.0, 2.0 and 3.5 with Reflector and a Form is definitely derived from IDisposable in all three. Form->ContainerControl->ScrollableControl->Control->Component->IComponent->IDisposable SignatureChris Tacke, eMVP Join the Embedded Developer Community http://community.opennetcf.com > Chris, > [quoted text clipped - 42 lines] >>> >>> Hilton Chris, >I just checked CF 1.0, 2.0 and 3.5 with Reflector and a Form is definitely >derived from IDisposable in all three. > > Form->ContainerControl->ScrollableControl->Control->Component->IComponent->IDisposable OK, so: Q1: Why does: using (Form form = new Form()) {} give the following compiler error: c:\test\FormDispose\Form1.cs(32): Cannot implicitly convert type 'System.Windows.Forms.Form' to 'System.IDisposable' ...and.. Q2: Why does: "(new Form () is IDisposable)" return false? Q1 is a compile time check, Q2 is a run-time and they're consistent. Hilton To follow-up my own post: When I run (FormDispose.exe) with the line: "MessageBox.Show (((new Form () is IDisposable).ToString()));" it returns *false*. This is using CF 1. Then I add the file FormDispose.exe.config so that FormDispose uses CF 2 and guess what? Yip, it returns *true*. Believe it, or not... Hilton > Chris, > [quoted text clipped - 21 lines] > > Hilton Well you have to believe the runtime. I can only conclude that I'm looking at the wrong 1.0 binary (or at least not the one your system is using). What version of 1.0 are you running? SignatureChris Tacke, eMVP Join the Embedded Developer Community http://community.opennetcf.com > To follow-up my own post: > [quoted text clipped - 36 lines] >> >> Hilton CF 1.0.4292.0 which is CF1 SP3 Try it, create a Pocket PC, add the line below and on CF 1, it shows false (and using doesn't compile either). Hilton > Well you have to believe the runtime. I can only conclude that I'm > looking at the wrong 1.0 binary (or at least not the one your system is [quoted text clipped - 40 lines] >>> >>> Hilton Free MagazinesGet these publications absolutely FREE for up to 12 months. 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