经常用的Lambda表达式 返回的是 Expression<T> 格式
public class ActivityService
{
private readonly List<Activity> _source = new List<Activity>(); public ActivityService()
{
_source.Add(new Activity()
{
Id = "5656d551d430520e100fa4f5" ,
Name="奥运会"
});
_source.Add(new Activity()
{
Id = "d702abd8",
Name = "亚运会"
});
_source.Add(new Activity()
{
Id = "706b0ba267a9",
Name = "美洲杯"
}); _source.Add(new Activity()
{
Id = "47d6",
Name = "世界杯"
});
_source.Add(new Activity()
{
Id = "4a8d",
Name = "大运会"
});
_source.Add(new Activity()
{
Id = "acdb",
Name = "欧洲杯"
});
} public Activity GetOne(Expression<Func<Activity, bool>> where)
{
var func = where.Compile();
return _source.FirstOrDefault(o => func(o)); }
}
public class Activity
{
public string Id { get; set; }
public string Name { get; set; } }
调用方式如下:
class Program
{
static void Main(string[] args)
{
ActivityService service=new ActivityService();
string id = string.Empty;
string name = "大运会"; //表达式不支持语句块
Expression<Func<Activity, bool>> expression =
(Activity a) => string.IsNullOrEmpty(id) ? a.Name == name : a.Id == id; //如果需要语句块 可以直接使用委托,然后有2种方法 (1)将其封装到Excepression (2)直接使用Lambda表达式
Func<Activity, bool> func = (a) =>
{
if (!string.IsNullOrEmpty(id))
return a.Id == id;
return a.Name == name;
};
//expression = (Activity a) => func(a);
//或者直接在下面使用Lambda
var activity2 = service.GetOne( (a)=>func(a)); var activity = service.GetOne(expression);
Console.Read();
}
}