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.NET Forum / Windows Forms / WinForm General / February 2007ReadOnlyAttribute
Hi there, Given a "PropertyGrid" with one particular property that appears as follows: -Size Width 10 Height 20 where "Size" is the native .NET "Size" structure, if the property is marked with the "ReadOnlyAttribute" then all three lines above appear grayed out as usual. However, if you replace "Size" with your own customized "Size" structure" instead (not inherited from the native .NET "Size" structure), then "Size" above will now be grayed out but not the "Width" and "Height" lines. Is there no way to propagate the "ReadOnlyAttribute" to all children or do we really have to handle this manually (by creating a read-only "PropertyDescriptor" for all children). Thanks. Sorry, I should clarify that the read-only attribute is applied at runtime (on-the-fly) depending on conditions. > Sorry, I should clarify that the read-only attribute is applied at > runtime (on-the-fly) depending on conditions. How are you applying attributes at runtime? As far as I'm aware, whether or not an attribute is applied to something is a compile-time decision, and can't be changed at runtime.  SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet If replying to the group, please do not mail me too > How are you applying attributes at runtime? As far as I'm aware, > whether or not an attribute is applied to something is a compile-time > decision, and can't be changed at runtime. You can create your own "PropertyDescriptor" objects at runtime and take complete control over your properties including their attributes (augmenting or overriding whatever you want). See "PropertyDescriptor.CreateAttributeCollection()" and "PropertyDescriptor.AttributesArray" for instance. Note that you can can take control over all types in general using the "TypeDescriptionProviderAttribute" (for 2.0 and later), "ICustomTypeDescriptor" and (to some extent) "TypeConverterAttribute". The documentation to figure this all out is no picnic however. BTW, "PropertyDescriptor.IsReadOnly", "PropertyDescriptor.IsBrowsable", etc. complicate things even further (noting that the latter property isn't event respected by the "PropertyGrid" but this is likely a bug and I've reported it to MSFT). > > How are you applying attributes at runtime? As far as I'm aware, > > whether or not an attribute is applied to something is a compile-time [quoted text clipped - 9 lines] > "ICustomTypeDescriptor" and (to some extent) "TypeConverterAttribute". The > documentation to figure this all out is no picnic however. Ah, I see - not like the normal way of applying attributes at all. If your property *starts off* read-only, is it greyed out in the property grid? I wonder whether it's not noticing the change. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet If replying to the group, please do not mail me too >> > How are you applying attributes at runtime? As far as I'm aware, >> > whether or not an attribute is applied to something is a compile-time [quoted text clipped - 13 lines] > > Ah, I see - not like the normal way of applying attributes at all. Yes, and I think the only time you typically have to resort to this is when you need to get granular control over a "PropertyGrid" at runtime (there is no other way AFAIK and the techniques are documented by both MSFT and others of course). Figuring out all the details is a huge pain however (and it takes an inordinate amount of code to implement ths simplest change). Is it just me or are the .NET docs in general very weak? > If your property *starts off* read-only, is it greyed out in the > property grid? I wonder whether it's not noticing the change. If I simply apply the read-only attribute to my customized "Size" property then it grays it out but not its sub-properties ("Width" and "Height"). You would think that it would but then again, my "Size" property is actually a member of a larger object which I'm customizing the properties for (using "PropertyDescriptor" objects). I see no reason why the read-only attribute shouldn't be propagated to children however (without manual intervention since again, it takes a lot of code to do this). > > If your property *starts off* read-only, is it greyed out in the > > property grid? I wonder whether it's not noticing the change. [quoted text clipped - 6 lines] > shouldn't be propagated to children however (without manual intervention > since again, it takes a lot of code to do this). Is your Size type definitely a struct and not a class? I wonder if that would make a difference - because strictly speaking, you could change the contents of a reference type object without changing which object was being referred to. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet If replying to the group, please do not mail me too > Is your Size type definitely a struct and not a class? I wonder if that > would make a difference - because strictly speaking, you could change > the contents of a reference type object without changing which object > was being referred to. Yes, it is a struct. I'm still experimenting but will likely toss in the towel and manually code things if I can't resolve it soon. Thanks again for your help. > > Is your Size type definitely a struct and not a class? I wonder if that > > would make a difference - because strictly speaking, you could change [quoted text clipped - 4 lines] > towel and manually code things if I can't resolve it soon. Thanks again for > your help. No problem (not that my help has been anything!) - but it does sound interesting. Could you post a short but complete program which demonstrates the problem? See http://www.pobox.com/~skeet/csharp/complete.html for details of what I mean by that. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet If replying to the group, please do not mail me too John you need to refresh the property gred after you change the attribute. Try applying RefreshPropertiesAttrubute as well. SignatureHTH Stoitcho Goutsev (100) Sorry, I should clarify that the read-only attribute is applied at runtime (on-the-fly) depending on conditions. Thanks. I'm already applying it with no effect however. Note that it's not grayed out even if I apply the read-only attribute at compile time (to the "Size" property). Since I'm customizing "PropertyDescriptor" objects at a higher level however, that may be impacting things but I don't know why. It seems counter-intuitive.to me (I think it should work regardless IOW). John you need to refresh the property gred after you change the attribute. Try applying RefreshPropertiesAttrubute as well. -- HTH Stoitcho Goutsev (100) "John Allen" <no_spam@_nospam.com> wrote in message news:OiuprfDVHHA.388@TK2MSFTNGP04.phx.gbl... Sorry, I should clarify that the read-only attribute is applied at runtime (on-the-fly) depending on conditions. 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 ...
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