A) In the following code, will the method DataTools.LoadSearchList() only be called once, or every time the property is being accessed?
public static IEnumerable<string> SearchWordList
{
get
{
return DataTools.LoadSearchList();
}
}B) Is there any difference to this?
public static IEnumerable<string> SearchWordList = DataTools.LoadSearchList();
Properties and fields behave entirely differently, even though they might appear similar from a coding point of view.
A property is actually just a shortcut for a pair of get/set methods, and like any method, the body will be executed each time you call it..
回答:
In your first example, LoadSearchList() will be called each time the property is accessed.
In the second, LoadSearchList() will only be called once (but it will be called whether you use it or not since it is now a field rather than a property).
A better option might be:
private static IEnumerable<string> _searchWordList;
public static IEnumerable<string> SearchWordList
{
get
{
return _searchWordList ??
( _searchWordList = DataTools.LoadSearchList());
}
}Or if you're using .NET 4.0 and want something thread-safe you can use Lazy<T>, as Jon Skeet mentioned (I think the syntax should be correct, but don't hold me to it):
private static Lazy<IEnumerable<string>> _searchWordList =
new Lazy<IEnumerable<string>>(() => DataTools.LoadSearchList());
public static IEnumerable<string> SearchWordList
{
get { return _searchWordList.Value; }
}