Say I have the following classes:
public class BaseConfig
{
}
public class SpecialConfig : BaseConfig
{
}
Then I have a generic class definition that will contain these:
public class ConfigList<T> : ObservableCollection<T> where T : BaseConfig
{
}
Then I have another class where I want to have a collection of ConfigList objects:
public class ConfigurationManager
{
private ObservableCollection<ConfigList<BaseConfig>> _configItems
public ConfigurationManager()
{
_configItems = new ObservableCollection<ConfigList<BaseConfig>>();
}
public void AddConfigList(ConfigList<BaseConfig> configList)
{
_configItems.Add(configList);
}
}
Then elsewhere in application code I have this:
ConfigurationManager _manager = new ConfigurationManager();
ConfigList<SpecialConfig> _configuration = new ConfigList<SpecialConfig>();
For some odd reason, I thought C# would allow the following due to inheritance, but it doesn't. What I want to know is how can I accomplish adding an object to a collection of a generic type of class like i'm doing below (This is surely a common problem people encounter and surely there's a simple pattern/solution to accomplish this):
_manager.AddConfigList(_configuration);
It will not work this way, but luckily you can work around by taking advantage of co-variance in generic , define one new co-variance interface:
public interface IConfigList<out T>
{
}
So your ConfigList inherits this interface:
public class ConfigList<T> : ObservableCollection<T>, IConfigList<T>
where T : BaseConfig
{
}
And your ConfigurationManager
uses IConfigList
instead of ConfigList
public class ConfigurationManager
{
private ObservableCollection<IConfigList<BaseConfig>> _configItems;
public ConfigurationManager()
{
_configItems = new ObservableCollection<IConfigList<BaseConfig>>();
}
public void AddConfigList(IConfigList<BaseConfig> configList)
{
_configItems.Add(configList);
}
}
Then it will work:
ConfigurationManager _manager = new ConfigurationManager();
IConfigList<BaseConfig> _configuration = new ConfigList<SpecialConfig>();
_manager.AddConfigList(_configuration);
您需要利用泛型协方差来实现这一目标。
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