我如何使用contains和indexof？ [英] How can I use contains and indexof?

问题描述

如果drank.contains doenst似乎有效。有人可以帮我吗？



我尝试过：

 public partial class Form1：Form 
 {
 
 administration admin = new administration（）; 
 // reserveer Reserveer = new reserveer（）; 
 public Form1（）
 {
 InitializeComponent（）; 
 
 load（）; 
} 
 
 
 public void load（）
 {
 List< groep> Groepnaam = admin.groepsnaam（）; 
列表< persoon> personen = admin.spelers（）; 
 
 foreach（Groepnaam的Groep naam）
 {
 listBox3.Items.Add（naam.Groepsnaam）; 
 
} 
 foreach（persoon Persoon in personen）
 {
 listBox1.Items.Add（Persoon）; 
} 
} 
 
 
 
 private void button1_Click（object sender，EventArgs e）
 {
 int aantalstrikes = Convert。 ToInt32（numstrikes.Value）; 
 int aantalspares = Convert.ToInt32（numspares.Value）; 
 int aantalpunten = Convert.ToInt32（tbpunten.Text）; 
 int aantalbier = Convert.ToInt32（aantbier.Text）; 
 int prijs = 2; 
 
 
 admin.voegtoebier（aantalbier，prijs）; 
 
 admin.voegtoescore（aantalpunten，aantalstrikes，aantalspares）; 
列表<得分> Punten = admin.punten（）; 
 
 foreach（在Punten得分）
 {
 listBox2.Items.Add（punt）; 
 
 
 
} 
 List< bier> consumptie = admin.Bier（）; 
 
 foreach（bier在消费中喝酒）
 {
 listBox4.Items.Add（drank）; 
 
 
 
} 
 if（drank.contains）
 {
 
 
} 
 
 
 
 
} 

解决方案

首先，喝了在您的代码到达 foreach 循环结束时超出范围 - 所以无论它是什么，您都无法使用它 - 它不再存在。



其次，Contains和IndexOf需要一个实现IEnumerable< T>的类。所以除非 bier 类实际上是从List或类似的派生，或者你自己添加了一个Contains方法，否则你无法调用它。从上面的代码来看，我认为不是。

这就是你想要做的事情，我想：

  public   class 啤酒
 {
  public   string 名称{ get ;  set ; } 
  public   int  Abv { get ;  set ; } 
} 
 私有  void  MyButton_Click（ object  sender，EventArgs e）
 {
 List< Beer> beers =  new  List< Beer>（）; 
 Beer a =  new  Beer（）{Name =   Shimptons Old Cleanser，Abv =  17 }; 
 beers.Add（a）; 
 Beer b =  new  Beer（）{Name =   Horse Urine，Abv =  3 }; 
 beers.Add（b）; 
 Beer c =  new  Beer（）{Name =   Heinekon，Abv =  1 }; 
 beers.Add（c）; 
  if （beers.Contains（b））
 {
 Console.WriteLine（  是的，{0}是啤酒。技术上。，b.Name）; 
} 
 Console.WriteLine（  {0}位于索引{1}，c.Name，beers.IndexOf（c））; 
 ... 

Quote：< / div >排序好，我想检查一个来自sql数据库的值（int）。但是我在哪里可以使用contains方法来检查我的数据库中是否有一个例如10​​0的数字。

基本上，不要。



如果你想知道数据库中是否存在某些内容，请询问数据库！

  SELECT  COUNT（*） FROM  MyTable  WHERE  MyColumn =  100  

将它与ExecuteScalar一起使用，它将返回具有该值的项目数。



如果你已经将它们构建成 bier 对象的集合，那么请使用Linq Exists方法：

  if （beers.Exists（x = >  x.Abv =  3 ））
 {
 Console.WriteLine（ 是，{0}是啤酒。技术上。，b.Name）; 
} 

Contains方法只查找对集合中对象引用的对象引用的完全匹配，它不能查看对象内部

if drank.contains doenst seem to work. can someone help me with that?

What I have tried:

public partial class Form1 : Form
    {

        administration admin = new administration();
        //reserveer Reserveer = new reserveer();
        public Form1()
        {
            InitializeComponent();

            load();
        }


        public void load()
        {
            List<groep> Groepnaam = admin.groepsnaam();
            List<persoon> personen = admin.spelers();
            
            foreach (Groep naam in Groepnaam)
            {
                listBox3.Items.Add(naam.Groepsnaam );

            }
            foreach (persoon Persoon in personen)
            {
                listBox1.Items.Add(Persoon);
            }
        }
        

        
        private void button1_Click(object sender, EventArgs e)
        {
            int aantalstrikes = Convert.ToInt32(numstrikes.Value);
            int aantalspares = Convert.ToInt32(numspares.Value);
            int aantalpunten = Convert.ToInt32(tbpunten.Text);
            int aantalbier = Convert.ToInt32(aantbier.Text);
            int prijs = 2;
            

            admin.voegtoebier(aantalbier, prijs);
            
            admin.voegtoescore(aantalpunten, aantalstrikes, aantalspares);
            List<score> Punten = admin.punten();
            
            foreach (score punt in Punten)
            {
                listBox2.Items.Add(punt);
                


            }
            List<bier> consumptie = admin.Bier();
            
            foreach(bier drank in consumptie)
            {
                listBox4.Items.Add(drank);
                


            }
              if (drank.contains)
            {


             }




        }

解决方案

First off, drank is out of scope by the time your code gets to the end of the foreach loop - so no matter what it was, you can't use it - it no longer exists.

Secondly, Contains and IndexOf require a class that implements IEnumerable<T> so unless the bier class is actually a derived from a List or similar, or you added a Contains method to it yourself, you can't call it. And from the code above that, I don't think it is.
This is what you are trying to do, I think:

public class Beer
    {
    public string Name { get; set; }
    public int Abv { get; set; }
    }
private void MyButton_Click(object sender, EventArgs e)
    {
    List<Beer> beers = new List<Beer>();
    Beer a = new Beer() { Name = "Shimptons Old Cleanser", Abv = 17 };
    beers.Add(a);
    Beer b = new Beer() { Name = "Horse Urine", Abv = 3 };
    beers.Add(b);
    Beer c = new Beer() { Name = "Heinekon", Abv = 1 };
    beers.Add(c);
    if (beers.Contains(b))
        {
        Console.WriteLine("Yes, {0} is a beer. Technically.", b.Name);
        }
    Console.WriteLine("{0} is at index {1}", c.Name, beers.IndexOf(c));
...

Quote:</div>well sort off, i want to check a value (int) that comes from a sql database. but where can i use the contain method to check if there is an number for example 100 in my database.

Basically, don't.

If you want to know if something exists in a DB, ask the DB!

SELECT COUNT(*) FROM MyTable WHERE MyColumn = 100

Use that with ExecuteScalar, and it will return the number of items with that value.

If you have built them into a collection of bier objects, then use the Linq Exists method instead:

if (beers.Exists(x => x.Abv = 3))
    {
    Console.WriteLine("Yes, {0} is a beer. Technically.", b.Name);
    }

The Contains method only looks for an exact match on an object reference to an object reference in the collection, it can't look at the object internals.

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