ListBox1.Items.Clear(); Does not work in Generic Collection

Arun Kurmi

hi friends how are you..........
Today I have 2 Questions...
(1)
------------------
ListBox1.Items.Clear(); not work on Generic collection Example.
I have tried 2 example 1)List
2)LinkedList

Code of First Example are:

listBox1.Items.Clear();

//lst.Clear();

for (int i = 0; i < lst.Count; i++)

{

listBox1.Items.Add(lst[i]);

}

private void button1_Click(object sender, EventArgs e)

{

lst.Add("Red");

lst.Add("green");

lst.Add("blue");

lst.Add("pink");

lst.Add("lemon");

LoadMyList();

button2.Enabled = true;

button3.Enabled = true;

button4.Enabled = true;

}
___________________________________________________________________
(2)
-----------------
I have seen both List and LinkedList Example but never found any difference in both so questiion are what are the difference in both.If Possible Please gave an Example.

4 Replies

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Vulpes13y ago
Well, I notice there that you don't disable button1 after it has been pressed. So, if it is pressed again, then it will look like the existing items are not being cleared from the listbox because they haven't been cleared from the List itself and so will be displayed again.

To deal with that just insert the highlighted line:

private void button1_Click(object sender, EventArgs e)
{
lst.Clear();
lst.Add("Red");
lst.Add("green");
lst.Add("blue");
lst.Add("pink");
lst.Add("lemon");
LoadMyList();
button2.Enabled = true;
button3.Enabled = true;
button4.Enabled = true;
}
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Arun Kurmi13y ago
but not work in my machine .when click to add button it not clear previous and and items after prev. items.

This is my full code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using Microsoft.VisualBasic;

namespace Generics_OR_GenericCollection
{
public partial class List_T_EX : Form
{
List lst = new List(); // creation of List Class object. We use List class for string.
public List_T_EX()
{
InitializeComponent();
}

private void List_T_EX_Load(object sender, EventArgs e)
{
button3.Enabled = false;
button2.Enabled = false;
button4.Enabled = false;
}

private void button1_Click(object sender, EventArgs e)
{
lst.Add("Red");
lst.Add("green");
lst.Add("blue");
lst.Add("pink");
lst.Add("lemon");
LoadMyList();
button2.Enabled = true;
button3.Enabled = true;
button4.Enabled = true;
}

public void LoadMyList()
{
listBox1.Items.Clear();
//lst.Clear();
for (int i = 0; i < lst.Count; i++)
{
listBox1.Items.Add(lst[i]);
}
}

private void button2_Click(object sender, EventArgs e)
{
string str2 = Microsoft.VisualBasic.Interaction.InputBox("Enter Color name to insert in List", "Insert Box", "Replace this to color name", 0, 0);
string str1 = Microsoft.VisualBasic.Interaction.InputBox("Enter index no. to insert coler in List", "Insert Box", "Replace this to index", -1, -1);
//lst.Insert(2, "orange");
//lst.Insert(2,str2);
lst.Insert(Convert.ToInt32(str1), str2);
LoadMyList();
}

private void button3_Click(object sender, EventArgs e)
{
//if (listBox1.SelectedIndex > 0) //if we take 0 then first index not remove so take -1;
if (listBox1.SelectedIndex > -1)
{
//listBox1.Items.RemoveAt(listBox1.SelectedIndex);
lst.RemoveAt(listBox1.SelectedIndex);
LoadMyList();
}
else
{
Interaction.MsgBox("Please select an item before Removing");
}
}

private void button4_Click(object sender, EventArgs e)
{
lst.Reverse();
LoadMyList();
}
}
}
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Sanjeeb Lenka13y ago
The code is just working fine.
i take one listbox and two button for test

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class Default3 : System.Web.UI.Page
{
    List lst = new List();

    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        ListBox1.Items.Clear();
        ListBox1.Items.Add("Purple");
        ListBox1.Items.Add("Magenta");
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        lst.Add("Red");
        lst.Add("green");
        lst.Add("blue");
        lst.Add("pink");
        lst.Add("lemon");
        LoadMyList();
    }
    private void LoadMyList()
    {
        ListBox1.Items.Clear();
        //lst.Clear();
        for (int i = 0; i < lst.Count; i++)
        {
            ListBox1.Items.Add(lst[i]);
        }
    }

}

check on button 1 click it will clear the list box and add the content.

then button2 click it will clear the list box again and list item values.
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Vulpes13y ago
This code is working fine for me:

public partial class Form1 : Form
{
List lst = new List();

public Form1()
{
InitializeComponent();
listBox1.Items.Add("Purple");
listBox1.Items.Add("Magenta");
}

private void LoadMyList()
{
listBox1.Items.Clear();
//lst.Clear();
for (int i = 0; i < lst.Count; i++)
{
listBox1.Items.Add(lst[i]);
}
}

private void button1_Click(object sender, EventArgs e)
{
lst.Add("Red");
lst.Add("green");
lst.Add("blue");
lst.Add("pink");
lst.Add("lemon");
LoadMyList();
button2.Enabled = true;
button3.Enabled = true;
button4.Enabled = true;
}
}
}

Initially, Purple and Magenta are showing in the ListBox but when the button is pressed, they're gone and replaced by Red, green etc.

List and LinkedList differ in the way that elements are stored and retrieved.

With List, the elements are stored internally in an array of T. As more elements are added the array is doubled in size. This is done by creating a new array of the required size and copying the original ones into it. Elements are retrieved by index just as you would with an array.

In contrast, LinkedList is implemented as a chain of nodes in which each node references the node before, the node after and the actual element itself. It's main benefit is that an element can always be inserted quickly at any position in the linked list because all you need to do is to create a new node and update the pointers in the previous and next nodes to point to it. However, retrieval tends to be slow as the elements are not indexed.

As a general rule, stick with List unless you know that a lot of insertions (as opposed to additions) are going to be required.

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