CODEWITHSUNDEEP
c#winformslist
Messerschmitt
Messerschmitt

Reputation: 75

How to get the previous value in a list of strings in c#?

I'm trying to implement a previous and next buttons.

I have a list of string called list1 which is filled with whatever is a user has inputted from a textbox. I can't access the previous (not the last) string in the list. IndexOf method isn't useful as I don't know what user will input. 

private void previousBtn_click(object sender, EventArgs e)
{ 
    getList();
    int min = 0;
    int max = list1.Count;
    if(max==min)
    {
        previousBtn.Visible = false;
    }
    else
    {
        int temp =list.Count-1;
        //how do I get my string if I know the element index from the previous line?
        //textbox1.Text = thatPreviousString; 
    }
}

Sorry, it should be easy but I can't figure it out. How can I actully get my previous string in the list if the value is kind of unknown to me, so I can't just use find() and indexOf. MSDN shows that there is a property called Item but there is no proper tutorial or code bit that shows how to use it.

UPDATE: Let's say the user has typed "www.google.com", "www.facebook.com", "twitter.com" and then "www.yahoo.com". This urls are saved in list1. The last one was "www.yahoo.com", I can get it by calling Last(). The user can press the previous button anytime, so I can't specify the number of elements in list1, it's growing dynamically. I can only get the number of elements by calling 

list1.Count and the last index by calling list1[list1.Count-1]

Now I know the number of indexes and elements, so how do I get the previous string, e.g. "www.twitter.com", if I can only say I can give you the index, give my string back?

By the way, ElementAs is only for arrays, doesn't work for lists.

Upvotes: 0

Views: 1808

Answers (2)

David Arno
David Arno

Reputation: 43264

string temp =list[list.Count-1]; will give you the last element in the list.

string temp =list[list.Count-2]; will give you the previous element.

Remember, lists are 0-indexed, ie the first element is accessed via [0], so the last element will be [list size - 1].

So in your case textbox1.Text = list[list.Count-2]; will write the previous string into the textbox.

However, that won't give you a proper previous functionality. Pressing previous again won't give you list[list.Count-3]. You could though have a currentIndex variable that you decrement whenever previous is pressed for example and do textbox1.Text = list[currentIndex].

Upvotes: 0

weston
weston

Reputation: 54801

how do I get my string if I know the element index from the previous line?

int prevIndex; // element index from the previous line that you know
string temp = list1[prevIndex - 1];

Upvotes: 3

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