Dynamically change properties returned by ICustomTypeDescriptor.GetProperties to readonly
I have a class which implements ICustomTypeDescriptor, and is viewed and edited by the user in a PropertyGrid. My class also has a IsReadOnly property which determines if the user will be able to save their changes later. I don't want to allow the user to make changes if they will not be able to save. So if IsReadOnly is true I want to override any properties that would otherwise be editable to be read-only in a property grid.
I'm trying to use the GetProperties method of ICustomTypeDescriptor to add a ReadOnlyAttribute to each PropertyDescriptor. But it doesn't seem to be working. Here's my code.
public PropertyDescriptorCollection GetProperties(Attribute[] attributes)
{
List<PropertyDescriptor> fullList = new List<PropertyDescriptor>();
//gets the base properties (omits custom properties)
PropertyDescriptorCollection de开发者_运维技巧faultProperties = TypeDescriptor.GetProperties(this, attributes, true);
foreach (PropertyDescriptor prop in defaultProperties)
{
if(!prop.IsReadOnly)
{
//adds a readonly attribute
Attribute[] readOnlyArray = new Attribute[1];
readOnlyArray[0] = new ReadOnlyAttribute(true);
TypeDescriptor.AddAttributes(prop,readOnlyArray);
}
fullList.Add(prop);
}
return new PropertyDescriptorCollection(fullList.ToArray());
}
Is this even the correct way to use TypeDescriptor.AddAttributes()? While debuging after the call the AddAttributes() prop still has the same number of attributes none of which are a ReadOnlyAttribute.
TypeDescriptor.AddAttributes
adds class-level attributes to a given object or object type, not property-level attributes. On top of that, I don't think it has any effect other than in the behavior of the returned TypeDescriptionProvider
.
Instead, I would wrap all the default property descriptors like this:
public PropertyDescriptorCollection GetProperties(Attribute[] attributes)
{
return new PropertyDescriptorCollection(
TypeDescriptor.GetProperties(this, attributes, true)
.Select(x => new ReadOnlyWrapper(x))
.ToArray());
}
where ReadOnlyWrapper
is a class like this:
public class ReadOnlyWrapper : PropertyDescriptor
{
private readonly PropertyDescriptor innerPropertyDescriptor;
public ReadOnlyWrapper(PropertyDescriptor inner)
{
this.innerPropertyDescriptor = inner;
}
public override bool IsReadOnly
{
get
{
return true;
}
}
// override all other abstract members here to pass through to the
// inner object, I only show it for one method here:
public override object GetValue(object component)
{
return this.innerPropertyDescriptor.GetValue(component);
}
}
精彩评论