Getting number of ITEMS in an array C#

Question

I need to insert a string (from one window(QueryBuilder)) into an array(of another window(Main)).

In the Main i have a method as

public void DisplayCalcQuery(string argFromQueryBuilder)
{ 
    int itemsInUserBuiltQueries = UserBuiltQueries.Count();
    UserBuiltQueries[itemsInUserBuiltQueries] = argFromQueryBuilder.ToString();
    //displayng the user built query(queries) on the stack panel meant to display it.
    foreach (string query in UserBuiltQueries)
    {
        CheckBox checkQueries = new CheckBox() { Content = query };
        stackPanel1.Children.Add(checkQueries);
        checkboxes.Add(checkQueries);
    }
}

Where UserBuiltQueries is declared as

string[] UserBuiltQueries;

However when from the other window i do

 backscreen.DisplayCalcQuery(ttextBox1.Text.ToString()); //where backscreen is the Main

The argument is passed well but i get an error as

{"Value cannot be null.\r\nParameter name: source"}

What did I do wrong ?

After initializing, UserBuiltQueries[itemsInUserBuiltQueries - 1] ? — Abhitalks
– Abhitalks, Commented Dec 5, 2013 at 9:06

Steve · Accepted Answer · 2013-12-05 09:16:21Z

These lines are wrong

int itemsInUserBuiltQueries = UserBuiltQueries.Count();
UserBuiltQueries[itemsInUserBuiltQueries] = argFromQueryBuilder.ToString();

Arrays start at index zero and end at index (Count - 1), so, if UserBuiltQueries.Count() returns 10 you could use indexes from 0 to 9. Essentially, using index 10, you are adding a new string outside the end of the array.

However, if your requirements force you to expand the array, it is better and more easy to code if you use a List<string> instead. Adding new elements will be a lot more easier and you could still use the List as an Array for common tasks.

    List<string> UserBuiltQueries = new List<string>();

    .....

    public void DisplayCalcQuery(string argFromQueryBuilder)
    { 
        UserBuiltQueries.Add(argFromQueryBuilder);

        //displayng the user built query(queries) on the stack panel meant to display it.
        foreach (string query in UserBuiltQueries)
        {
            CheckBox checkQueries = new CheckBox() { Content = query };
            stackPanel1.Children.Add(checkQueries);
            checkboxes.Add(checkQueries);
        }
    }

By the way, you should stop to unnecessarily convert a string to a string. You pass a ttextBox1.Text.ToString() but ttextBox1.Text is already a string. Inside the method the parameter argFromQueryBuilder is already a string and there is no need to convert to a string

Raimond Kuipers · Accepted Answer · 2013-12-05 09:10:00Z

1

Instead of using string[] for UserBuildQueries, use List. When you need it as an array, you can simply say: UserBuildQueries.ToArry()

Rewrite the function to

public void DisplayCalcQuery(string argFromQueryBuilder)
{ 
  UserBuiltQueries.Add(argFromQueryBuilder.ToString());
  //displayng the user built query(queries) on the stack panel meant to display it.
  foreach (string query in UserBuiltQueries)
  {
     CheckBox checkQueries = new CheckBox() { Content = query };
     stackPanel1.Children.Add(checkQueries);
     checkboxes.Add(checkQueries);
  }
}

answered Dec 5, 2013 at 9:10

Raimond Kuipers

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Comments

giammin · Accepted Answer · 2013-12-05 09:14:01Z

0

In c# but I think in all programming language indexis start from 0:

so if an array has length or count =1 the index is 0 array[0], array.lenght==1

int itemsInUserBuiltQueries = UserBuiltQueries.Count()-1;
UserBuiltQueries[itemsInUserBuiltQueries] = argFromQueryBuilder.ToString();

And double check that your array is initialized before using it!

edited Dec 5, 2013 at 9:14

answered Dec 5, 2013 at 9:08

giammin

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