我最近被一位同事问到:是否可以通过一个数组中的一个查询获取前五个元素和最后五个元素？
int[] someArray = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 };
我尝试过的:
int[] someArray = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 };
var firstFiveResults = someArray.Take(5);
var lastFiveResults = someArray.Skip(someArray.Count() - 5).Take(5);
var result = firstFiveResults;
result = result.Concat(lastFiveResults);
是否可以通过一个查询获取前五个元素和后五个元素？
我尝试使用C#DI方法来实现一些东西.以下是我的代码片段.
public interface IMessageService
{
void Send(string uid, string password);
}
public class MessageService : IMessageService
{
public void Send(string uid, string password)
{
}
}
public class EmailService : IMessageService
{
public void Send(string uid, string password)
{
}
}
和代码创建一个ServiceLocator:
public static class ServiceLocator
{
public static object GetService(Type requestedType)
{
if (requestedType is IMessageService)
{
return new EmailService();
}
else
{
return null;
}
}
}
现在,我用它创建一个测试代码
public class AuthenticationService
{
private IMessageService msgService;
public …我一直在使用C#编写计算器,遇到了一个我无法解决的问题.
目前,当用户输入除以零的数字时,答案默认为0.00,而应该是无效的.
我不知道为什么,经过一段时间的修修,我无法弄明白.这是相关代码:
private void button1_Click(object sender, EventArgs e)
{
double number1, number2, ans; // Identify variables as double to account for decimals.
number1 = Convert.ToDouble(num1.Text); // Convert the contents of the textBox into a double.
number2 = Convert.ToDouble(num2.Text); //
ans = 0.0;
string symbol = modifier1.Text;
if (symbol == "/" && number2 == 0) // This part seems to be broken.
answer.Text = "Invalid input.";
else
if (symbol == "+")
ans = number1 + number2;
else if (symbol == …为什么这段代码不运行,我想检查JSON是否包含key的整数PurchasedValue？():
public PropertyInfo(Newtonsoft.Json.Linq.JToken jToken)
{
this.jToken = jToken;
int PurchasedValue = (int)(jToken["PurchasedValue"].Value ?? 0);
}
错误是:
Error CS0019: Operator `??' cannot be applied to operands of type `method group' and `int' (CS0019)
这是一段代码:
Func<dynamic> f1 = new Func<dynamic>(() => 10);
Func<int> f2 = () => 10;
Console.Write(f1.Method.ReturnType);
Console.Write(" and " + f2.Method.ReturnType );
输出: System.Object and System.Int32
我的问题是:
为什么dynamicDLR(用于的类型)推断的类型dynamic是System.Object和不是System.Int32？这不是很合乎逻辑,因为它还涉及将Int32结构装箱到对象.
据我所知,当我们在这里检查类型时,我们会在执行时动态执行,因为我们使用Reflection.所以DLR当时知道它是int由于某种原因它把它装进Object......为什么？
我试图在SO上找到任何关于它的东西并用Google搜索,但我找不到任何解释这一切的答案.
鉴于以下课程:
public class Foo {
public Foo(int i, double d) {
Integer = i;
Double = d;
}
public int Integer {get;}
public double Double {get;}
private static Random rand = new Random();
public static Foo CreateRandom() => new Foo(rand.Next(1,101), rand.NextDouble());
}
以及这种用法:
void Main()
{
var items = Enumerable.Range(0, 50)
.Select(_ => Foo.CreateRandom());
Console.WriteLine(items.Sum(GetInteger)); // Fine
Console.WriteLine(items.Sum(GetDouble)); // Ambiguous
Console.WriteLine(items.Sum(x => x.Double)); // Also fine
Console.WriteLine(items.Sum((Func<Foo,double>)GetDouble)); // Cast required? Why?
int GetInteger(Foo item) => item.Integer;
double GetDouble(Foo item) => …所以,我正在阅读一篇文章,我遇到了一些让我质疑它的代码.
代码如下所示:
private UserService _userService = null;
protected UserService UserService
{
get { return _userService ?? Request.GetOwinContext().GetUserManager<UserService>(); }
}
对我来说,私有属性看起来总是为null,因此使用null-coalescing运算符是没用的.我想它和这样做很有用:
protected UserService UserService
{
get { return Request.GetOwinContext().GetUserManager<UserService>(); }
}
我错过了什么吗？虽然我们在讨论这个问题,但为什么这样做:
private UserService _userService = null;
肯定是这样的
private UserService _userService;
请帮我澄清一下我的怀疑:D