//构造函数私有化保证只能由类的静态方法实例化.当然，如果为public也是可以的，这里做只是为了统一构造入口,
//便于管理和维护。
private MyDependencyProperty(string name, Type propertyType, Type ownerType, MyPropertyMetadata propertyMetadata)
{
_propertyType = propertyType;
_ownerType = ownerType;
_name = name;
_propertyMetadata = propertyMetadata;
}
//依赖属性实例化工厂方法类.
public static MyDependencyProperty Register(string name, Type propertyType, Type ownerType, MyPropertyMetadata propertyMetadata)
{
if (propertyMetadata != null && propertyMetadata.DefaultValue.GetType() != propertyType)
{
throw new Exception(string.Format("the type of defaultValue is not {0}", propertyType.Name));
}
MyDependencyProperty dp = new MyDependencyProperty(name, propertyType, ownerType, propertyMetadata);
return(dp);
}
