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.NET Forum / .NET Framework / CLR / June 2004hook with reflection?
Hello ALL Does any one know if there is the way "to hook" method in the object using reflection? I don't want to override class (construct new one) but what I want is simply replace one method with another on run time. This method is virtual (overridden from abstract) so i guess it is possible.. How ? The problem concretization: Replace Paint(...) method defined in the DataGridTextBoxColumn class (and declared in DataGridColumnStyle class) on run-time. > Does any one know if there is the way "to hook" method in the object > using > reflection? No, there is none. > I don't want to override class (construct new one) but what I want is > simply > replace one method with another on run time. This method is virtual > (overridden from abstract) so i guess it is possible.. How ? If you really need to do it at runtime, you can use Reflection.Emit to create a dynamic assembly and class and override the method there. You cannot simply replace the method, unless you ressort to the unmanaged profiling API, which supports method replacement at load-time (and which I would not recommend for a real application). Fabian Hello Fabian, Thank you for your reply. Other question: May be it is possible to invoke my code exactly before this method [ in my case Paint(...) ] starts running? I just wonder if there is the way to implement something like "artifical" event using the reflection or may be other api? In my concreate task I need to change DataGridTextBoxColumn.DataGridTableStyle.BackBrush field value (at run-time) just before Paint(..) starts? (BTW: many thanks to Lutz Roeder for his .NET Reflector http://www.aisto.com/roeder/dotnet/) > > Does any one know if there is the way "to hook" method in the object > > using [quoted text clipped - 14 lines] > > Fabian > May be it is possible to invoke my code exactly before this method [ in > my > case Paint(...) ] starts running? I just wonder > if there is the way to implement something like "artifical" event using > the > reflection or may be other api? I'm sorry, I don't think there is an easy way to do this. > In my concreate task I need to change > DataGridTextBoxColumn.DataGridTableStyle.BackBrush field value (at > run-time) > just before Paint(..) starts? Why do you need to this? Can't you do it some time beforehand? What's the reason you can't you derive your own class from the column class and override the Paint method? Fabian > > In my concreate task I need to change > > DataGridTextBoxColumn.DataGridTableStyle.BackBrush field value (at > > run-time) > > just before Paint(..) starts? > Why do you need to this? This is the development of ExtenderProvider idea. I wanted to create something that can be named as "DataTableColumnStyle extender" :-) ... > Can't you do it some time beforehand? What's the > reason you can't you derive your own class from the column class and > override the Paint method? In my case this is possible. Here I'm looking for best design solution. Thank you Fabian. > This is the development of ExtenderProvider idea. I wanted to create > something that can be named as "DataTableColumnStyle extender" :-) ... One thing I could think of is to create create an in-memory class derived from the DataGridTextBoxColumn class (using CodeDom or Reflection.Emit, as I said). >> Can't you do it some time beforehand? What's the >> reason you can't you derive your own class from the column class and >> override the Paint method? > > In my case this is possible. Here I'm looking for best design solution. I fear, there is not much you can do with the possibilities provided by Reflection (or .NET), apart from what I mentioned. I guess to get the best design solution, you would need to use aspects. But I don't know of any functional aspect-oriented programming tool for .NET you could use. Fabian  SignatureUsing Opera's revolutionary e-mail client: http://www.opera.com/m2/ BTW other question: If it is impossible to "override" abstract method at run-time, how it is possible to add methods at run-time ? I have read something about it. What I remember that Invoke (or InvokeBegin / InvokeEnd ?) methods are "constructed" (in some way, really I don't imagine what does it mean) at run-time ... > > Does any one know if there is the way "to hook" method in the object > > using [quoted text clipped - 14 lines] > > Fabian > If it is impossible to "override" abstract method at run-time, how it is > possible to add methods at run-time ? I have read something about it. > What I > remember that Invoke (or InvokeBegin / InvokeEnd ?) methods are > "constructed" (in some way, really I don't imagine what does it mean) at > run-time ... They are provided by the runtime, i.e. the CLR. If you use Rotor, you can change it's sources to allow your own methods to be runtime-provided, but with ordinary .NET, you can not employ this mechanism for your problem. Fabian SignatureUsing Opera's revolutionary e-mail client: http://www.opera.com/m2/
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