How to the set Browsable attribute to True at runtime?

Question

Hi i have Browsable attributes based on which i need to load the properties at run time.

In order to make it more clear i have a dropdown list where i will select any one option amongst 1,2,3. If 1 is selected i should load the properties based on that accordingly for 2 and 3. The problem here is i have some specific properties for each option i.e 1,2 and 3. The options 1 or 2 or 3 will change dynamically how to change dynamically which property should be loaded dynamically.

Hence what i am trying to do is setting Browsable property to false at design time and change the property to true based on the selected option.
Is there anything better i can do? And also how to set the Browsable property to true at run time?

Vulpes · Answer

Well it is possible to change the value of the Browsable attribute at runtime using reflection. However as the attribute's Browsable property is read-only you have to change the value of its private underlying 'browsable' field instead so it's a bit of a hack. Whether it will then work properly in your scenario I don't know. Anyway here's some example C++/CLI code: #include stdafx.h using namespace System; using namespace System::ComponentModel; using namespace System::Reflection; ref class MyClass { int myField; public: [Browsable(false)] property int MyProperty { int get() { return myField; } void set(int value) { myField = value; } } }; int main(array ^args) { MyClass^ mc = gcnew MyClass(); Type^ t = mc->GetType(); PropertyInfo^ pi = t->GetProperty(MyProperty); Type^ bt = BrowsableAttribute::typeid; array ^ attrs = safe_cast ^>(pi->GetCustomAttributes(bt false)); Console::WriteLine(Initial value of attribute is {0} attrs[0]->Browsable); // get private browsable field using reflection and set it to true BindingFlags bf = BindingFlags::Instance | BindingFlags::NonPublic; FieldInfo^ fi = bt->GetField(browsable bf); fi->SetValue(attrs[0] true); Console::WriteLine(Revised value of attribute is {0} attrs[0]->Browsable); Console::ReadKey(); return 0; }

Vulpes · Answer

If you check the documentation for the PropertyGrid: http://msdn.microsoft.com/en-us/library/system.windows.forms.propertygrid.aspx it says: To use the property grid you create a new instance of the PropertyGrid class on a parent control and set SelectedObject to the object to display the properties for. The information displayed in the grid is a snapshot of the properties at the time the object is assigned. If a property value of the object specified by the SelectedObject is changed in code at run time the new value is not displayed until an action is taken in the grid that causes the grid to refresh. As you're still using the same object that was originally assigned (albeit with the Browsable attribute of one of its properties changed) I'd try initially: MainForm::app_main_form->propertyGrid1->Refresh(); If that doesn't work I'd try: MainForm::app_main_form->propertyGrid1->SelectedObject = null; // remove object MainForm::app_main_form->propertyGrid1->SelectedObject = MainForm::screen_setting; // re-assign MainForm::app_main_form->propertyGrid1->Refresh();

Karthik Agarwal · Answer

if(screen_setting->Type->Equals(DEBUG)) { Type ^ t = screen_setting->GetType(); PropertyInfo ^ pi = t->GetProperty(BGColor); Type ^ bt = BrowsableAttribute::typeid; array ^ attrs = safe_cast ^>(pi->GetCustomAttributes(bt true)); // get private browsable field using reflection and set it to true BindingFlags bf = BindingFlags::Instance | BindingFlags::NonPublic; FieldInfo^ fi = bt->GetField(Browsable bf); fi->SetValue(attrs[0] false); /*AttributeCollection^ attributes = TypeDescriptor::GetProperties(srcimg)[ BGColor ]->Attributes; attributes[ BrowsableAttribute::typeid ] = BrowsableAttribute::Yes; */ } MainForm::app_main_form->propertyGrid1->SelectedObject = MainForm::screen_setting; Hi Vulpes this is what xtactly i am doing in run time based upon some conditon i want to make this property to false [Browsable(true)] property Color BGColor { Color get() { return bg_color; } void set( Color val ) { bg_color = val; } } But i am getting following Exception An unhandled exception of type 'System.NullReferenceException' occurred in viewer.exe Additional information: Object reference not set to an instance of an object. so could u plz tell me to which object i am not setting the reference? Also tell me how to refresh this Browsable attribute

Vulpes · Answer

Well I don't know what you've done to load the Properties pane for the object in the first place but whatever it is you're going to need to refresh it so it can take account of the revisions to the Browsable attributes.

Karthik Agarwal · Answer

Ok got it PresentationHandler itself is a property and it has only one Browsable Attribute and just like PresentationHandler i have a few other properties which are Browsable of its kind. So is there any modification which i require to do for this case. And I have tried as below but nothing turned up Type ^ t = ScreenSetting::GetType(); PropertyInfo ^ pi = t->GetProperty(PresentationHandler); Type ^ bt = BrowsableAttribute::typeid; array ^ attrs = safe_cast ^>(pi->GetCustomAttributes(bt false)); // get private browsable field using reflection and set it to true BindingFlags bf = BindingFlags::Instance | BindingFlags::NonPublic; FieldInfo^ fi = bt->GetField(browsable bf); fi->SetValue(attrs[0] true); Is there anything else i should be doing apart from this in order see that property on the Form. And the property declaration is as follows: [Browsable (false)] property String ^ PresentationHandler { String ^ get() { return pres_handler; } void set( String ^ val ) { pres_handler = val; } }

Vulpes · Answer

I mean there's only one Browsable attribute on the PresentationHandler property - it's possible to have multiple attributes of the same type on the same property but I can't think of any reason why you'd want to do that here. You'd have to perform the same exercise on all other properties whose Browsable attribute you wish to change.

Karthik Agarwal · Answer

3. There's (presumably) only one Browsable attribute so we're only interested in attrs[0]. No Vulpes you mistook my words i was asking about one property to make it clear for you but there are many in number just like that. If this is the case what should be done.

Vulpes · Answer

What the code does is to: 1. Get a PropertyInfo object (pi) for the PresentationHandler property of the ScreenSetting class. 2. Get the custom attributes of pi (attrs) which are of type Browsable; as these are returned as an object array they need to be cast to a Browsable array. 3. There's (presumably) only one Browsable attribute so we're only interested in attrs[0]. 4. Get a FieldInfo object (fi) for the browsable field of the Browsable class; as this is an instance field and non-public we need to set the BindingFlags accordingly. 5. Set the value of this field for the attrs[0] object to true.

Karthik Agarwal · Answer

Ok Got it. But Can you explain in detail what that code means? I have tried this out but i am not clear about the implementation. What i did is i have a property PresentationHandler which i have set to false and if i write as below it should be visible in the property pane right? Type ^ t = ScreenSetting::GetType(); PropertyInfo ^ pi = t->GetProperty(PresentationHandler); Type ^ bt = BrowsableAttribute::typeid; array ^ attrs = safe_cast ^>(pi->GetCustomAttributes(bt false)); //Console::WriteLine(Initial value of attribute is {0} attrs[0]->Browsable); // get private browsable field using reflection and set it to true BindingFlags bf = BindingFlags::Instance | BindingFlags::NonPublic; FieldInfo^ fi = bt->GetField(browsable bf); fi->SetValue(attrs[0] true); //Console::WriteLine(Revised value of attribute is {0} attrs[0]->Browsable); //Console::ReadKey();

Vulpes · Answer

That's because TypeId should be typeid.

Karthik Agarwal · Answer

Vulpes Compilation errors in this line Type ^ bt = BrowsableAttribute::TypeId; The errors are as follows: error C2597: illegal reference to non-static member 'System::Attribute::TypeId' error C2843: 'System::Attribute::TypeId' : cannot take the address of a non-static data member or method of a managed type error C3142: 'System::Attribute::TypeId' : you cannot take the address of a property error C2440: 'initializing' : cannot convert from '' to 'System::Type ^'