与其他人建议的不同，这是很有可能的，而且也不那么难。例如，您想添加some新属性some属性，您可以在运行时根据某些条件选择这些属性。
我们需要两个辅助类来实现这个。
首先PropertyOverridingTypeDescriptor，它允许我们提供我们自己的属性描述符some属性，同时保持其他属性完好无损：
public class PropertyOverridingTypeDescriptor : CustomTypeDescriptor
{
private readonly Dictionary<string, PropertyDescriptor> overridePds = new Dictionary<string, PropertyDescriptor>();
public PropertyOverridingTypeDescriptor(ICustomTypeDescriptor parent)
: base(parent)
{ }
public void OverrideProperty(PropertyDescriptor pd)
{
overridePds[pd.Name] = pd;
}
public override object GetPropertyOwner(PropertyDescriptor pd)
{
object o = base.GetPropertyOwner(pd);
if (o == null)
{
return this;
}
return o;
}
public PropertyDescriptorCollection GetPropertiesImpl(PropertyDescriptorCollection pdc)
{
List<PropertyDescriptor> pdl = new List<PropertyDescriptor>(pdc.Count+1);
foreach (PropertyDescriptor pd in pdc)
{
if (overridePds.ContainsKey(pd.Name))
{
pdl.Add(overridePds[pd.Name]);
}
else
{
pdl.Add(pd);
}
}
PropertyDescriptorCollection ret = new PropertyDescriptorCollection(pdl.ToArray());
return ret;
}
public override PropertyDescriptorCollection GetProperties()
{
return GetPropertiesImpl(base.GetProperties());
}
public override PropertyDescriptorCollection GetProperties(Attribute[] attributes)
{
return GetPropertiesImpl(base.GetProperties(attributes));
}
}
几点说明：
- 构造函数需要
ICustomTypeDescriptor，不用担心，我们可以为任何类型或其实例获取一个TypeDescriptor.GetProvider(_settings).GetTypeDescriptor(_settings)其中 _settings 可以是Type or object那种类型的。
-
OverrideProperty正是我们所需要的，稍后会详细介绍。
我们需要的另一个类是TypeDescriptionProvider这将返回我们的自定义类型描述符而不是默认类型描述符。这里是：
public class TypeDescriptorOverridingProvider : TypeDescriptionProvider
{
private readonly ICustomTypeDescriptor ctd;
public TypeDescriptorOverridingProvider(ICustomTypeDescriptor ctd)
{
this.ctd = ctd;
}
public override ICustomTypeDescriptor GetTypeDescriptor (Type objectType, object instance)
{
return ctd;
}
}
相当简单：您只需在构造时提供类型描述符实例即可。
最后，处理代码。例如，我们希望所有以ConnectionString在我们的对象（或类型）中_settings可编辑System.Web.UI.Design.ConnectionStringEditor。为了实现这一点，我们可以使用这段代码：
// prepare our property overriding type descriptor
PropertyOverridingTypeDescriptor ctd = new PropertyOverridingTypeDescriptor(TypeDescriptor.GetProvider(_settings).GetTypeDescriptor(_settings));
// iterate through properies in the supplied object/type
foreach (PropertyDescriptor pd in TypeDescriptor.GetProperties(_settings))
{
// for every property that complies to our criteria
if (pd.Name.EndsWith("ConnectionString"))
{
// we first construct the custom PropertyDescriptor with the TypeDescriptor's
// built-in capabilities
PropertyDescriptor pd2 =
TypeDescriptor.CreateProperty(
_settings.GetType(), // or just _settings, if it's already a type
pd, // base property descriptor to which we want to add attributes
// The PropertyDescriptor which we'll get will just wrap that
// base one returning attributes we need.
new EditorAttribute( // the attribute in question
typeof (System.Web.UI.Design.ConnectionStringEditor),
typeof (System.Drawing.Design.UITypeEditor)
)
// this method really can take as many attributes as you like,
// not just one
);
// and then we tell our new PropertyOverridingTypeDescriptor to override that property
ctd.OverrideProperty(pd2);
}
}
// then we add new descriptor provider that will return our descriptor instead of default
TypeDescriptor.AddProvider(new TypeDescriptorOverridingProvider(ctd), _settings);
就是这样，现在所有属性都以ConnectionString将可通过编辑ConnectionStringEditor.
正如您所看到的，我们每次都只是重写默认实现的一些功能，因此系统应该相当稳定并按预期运行。
