如何使用linq查询分别从列表中获取键和值

Question

I started off using a randomized array for a quiz that I am doing, but after I got that working I realized that there was no way for me to be able to keep track of the answer that the user selected. I had been shown how to use some shuffle algorithm but it just confused me.

So I decided to create a List<KeyValuePair> to hold the answers from my dataset, the key is a string that is for the dataset row and the value is an integer, that is 1 for the correct answer then 0 for the wrong answer.

So what I am doing is, I have four buttons being stylized with css, I'm turning the button text into one of the four answers. This may sound like bad programming practice but its the only thing I can come up with and that is to change the tab order attribute to either a 1 or a 0 so I can keep track of the answer to display in a results page at the end.

The code I am using is this...

ds = MyDs(1);

System.Random rnd = new System.Random();

var QA = new List<KeyValuePair<string,int>>();

QA.Add(new KeyValuePair<string, int>(ds.Tables[0].Rows[0]["CorrectAnswer"].ToString(),1));
QA.Add(new KeyValuePair<string, int>(ds.Tables[0].Rows[0]["WrongAnswer1"].ToString(), 0));
QA.Add(new KeyValuePair<string, int>(ds.Tables[0].Rows[0]["WrongAnswer2"].ToString(), 0));
QA.Add(new KeyValuePair<string, int>(ds.Tables[0].Rows[0]["WrongAnswer3"].ToString(), 0));

var myQa = QA.OrderBy(c=> rnd.Next()).Select(c=>c.Key.ToString()).ToList();

Label5.Text = ds.Tables[0].Rows[0]["Question"].ToString();

Button1.Text = myQa[0].ToString();
Button2.Text = myQa[1].ToString();
Button3.Text = myQa[2].ToString();
Button4.Text = myQa[3].ToString();

this is fine when you look at myQa, the key shows up like it should but if I do this...

var myQa = QA.OrderBy(c=> rnd.Next()).Select(c=>c.Key.ToString() + c.Value.ToString()).ToList();

then my buttons text adds the key and value to the text, and I don't want that, I just want the key to show up in the button text, and then be able to access its value.

Any ideas or where I am missing something? I'm assuming that its in my query and I'm not sure how to fix it.

Thanks

Answer 1

Fundamentally, you need a Dictionary<TKey, TValue> .

Here:

var myQa = QA.OrderBy(c=> rnd.Next()).Select(c=>c.Key.ToString() + c.Value.ToString()).ToList();

you are selecting both key and its value . Instead you can just do:

var myQa = QA.OrderBy(c=> rnd.Next()).Select(c=>c.Key.ToString()).ToList(); to get the key

var kValue = QA.Where(m=> m.Key == "Correct Answer").FirstOrDefault().Value; <- willl get you a value for a particular key.

Answer 2

Actually you could use ToDictionary method instead of ToList. It accepts key selector and value selector parameters. And the you can

   var myQa = QA.OrderBy(c=> rnd.Next()).ToDictionary(ks=>ks.Key.ToString(), vs=>vs..Value.ToString());
   foreach(var keyValuePair in myQa)
   {
       Button button = new Button();
       button.Text = keyValuePair.Key;
       button.Tag= keyValuePair.Value;
       SomeParentControl.Controls.Add(button);
   }

In this way you'll have both the key and the value in one enumeration.

Also you can do like this:

   var myQaButtons = QA.OrderBy(c=> rnd.Next()).Select(c=>new Button{Text = c.Key, Tag = c.Value}).ToList();
   myQaButtons.ForEach(b=>SomeParentControl.Controls.Add(b));

Or simply

   var myQa = QA.OrderBy(c=> rnd.Next()).Select(c=>new {c.Key, c.Value}).ToList();

   Button1.Text = myQa[0].Key;
   Button1.Tag = myQa[0].Value
   Button2.Text = myQa[1].Key;
   Button2.Tag = myQa[1].Value;
   Button3.Text = myQa[2].Key;
   Button3.Tag = myQa[2].Value;
   Button4.Text = myQa[3].Key;
   Button4.Tag = myQa[3].Value;