|
Adding Items to a List Box |
|
The most important characteristic of a list box is the list
of items it contains. This list is represented by the Items property. The Items
list is created and managed by a ListBox-nested class named ObjectCollection.
ObjectCollection is a collection class that implements the IList,
the ICollection, and the IEnumerable interfaces.
At design time, to create a list of items, access the
Properties window of the list box and click the ellipsis button of the Items
field. This would open the String Collection Editor:
In the empty window, you can type an item, press Enter, add
another, and so on. After creating the list, you can click OK. To
programmatically add an item to the list, access the Items property, call its
Add() method, and pass the new item. You can do this continually for each item.
Here are examples:
private void InitializeComponent()
{
lbxFamily = new ListBox();
lbxFamily.Location = new Point(12, 12);
lbxFamily.Items.Add("Son");
lbxFamily.Items.Add("Daughter");
lbxFamily.Items.Add("Father");
lbxFamily.Items.Add("Mother");
Controls.Add(lbxFamily);
}
This would produce:
You can also first create an array of items and then add
that array to the collection. To support this, the ObjectCollection class
provides the AddRange() method. Here is an example:
private void InitializeComponent()
{
lbxFamily = new ListBox();
lbxFamily.Location = new Point(12, 12);
lbxFamily.Items.Add("Son");
lbxFamily.Items.Add("Daughter");
lbxFamily.Items.Add("Father");
lbxFamily.Items.Add("Mother");
string[] strMembers = { "Niece", "Nephew", "Uncle" };
lbxFamily.Items.AddRange(strMembers);
Controls.Add(lbxFamily);
}
This would produce:
If you use either the Add() or the AddRange()
method to add an item or a group of items, the item or the group would be added
to the end of the list, if a list exists already. To insert a new item somewhere
inside of the list, call the Insert() method.
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Practical Learning: Adding Items to a List Box
|
|
- On the form, click the Categories list box
- In the Properties window, click Items and click its ellipsis button
- Type Guitars and press Enter
- Type Bass and press Enter
- Complete the list to have the following items:
Guitars
Bass
Keyboards
Drums & Percussion
Band & Orchestra
Recording & Sound
Folk Instruments
Books & Videos
Accessories |
- Click OK
- To programmatically add items to the list boxes, on the form, double-click an unoccupied area to access its Load event and
implement it as follows:
private void MusicStore_Load(object sender, EventArgs e)
{
lbxTypes.Items.Add("Electric Guitars");
lbxTypes.Items.Add("Acoustic Guitars");
lbxTypes.Items.Add("Acoustic-Electric Guitars");
lbxTypes.Items.Add("Amplifiers");
lbxTypes.Items.Add("Effects");
lbxTypes.Items.Add("Microphones");
lbxTypes.Items.Add("Accessories");
lbxTypes.Items.Add("Value Packages");
}
|
- Execute the application to test it
- After using the form, close it and return your programming environment
- On the main menu, click Project -> Add Class...
- In the Templates list, make sure Class is select.
Set the name to PartDescription and click Add
- Complete the class as follows:
using System;
namespace MusicalInstrumentStore1
{
class PartDescription
{
private string number;
private string discr;
private decimal uprice;
public string PartNumber
{
get { return number; }
set { number = value; }
}
public string PartName
{
get { return discr; }
set { discr = value; }
}
public decimal UnitPrice
{
get { return uprice; }
set { uprice = value; }
}
public PartDescription()
{
this.number = "";
this.discr = "";
this.uprice = 0.00M;
}
public PartDescription(string nbr,
string name,
decimal price)
{
this.number = nbr;
this.discr = name;
this.uprice = price;
}
public override string ToString()
{
return this.PartNumber + " " +
this.PartName + " " +
this.UnitPrice.ToString();
}
}
}
|
- Access the MusicStore.cs file and create a few arrays as follows:
namespace MusicalInstrumentStore1
{
public partial class MusicStore : Form
{
string[] CatBass = {
"Electric Bass", "Acoustic-Electric Bass",
"Amplifiers", "Effects", "Accessories" };
string[] CatKeyboard = {
"Pianos", "Organs", "Synthesizers",
"Portable", "Workstations", "Arrangers",
"Stands", "Amps", "Pedals", "Accessories" };
string[] CatDrums = {
"Acoustic Drums", "Cymbals",
"Electronic Percussion", "World Percussion" };
string[] CatBand = {
"Trumpets", "Trombones", "Saxophones",
"Clarinets", "Flutes", "Baritones", "Tubas",
"Oboes", "Recorders", "Accessories" };
string[] CatAccessories = {
"Headphones", "Strings", "Slides", "Metronomes",
"Tuners", "Music Stands", "Cases", "Cables",
"Hearing Protection", "Electric Guitar Bags",
"Guitar Pedals", "Cleaning/Care" };
PartDescription[] ElectricGuitars =
{
new PartDescription("293027",
"Gibson Les Paul Vintage Solid Guitar",
850.75M),
new PartDescription("972355",
"Fender Standard Stratocaster Electric Guitar",
435.95M),
new PartDescription("390057",
"Gibson Les Paul Standard Left-Handed 50s Neck Electric Guitar",
2400.00M),
new PartDescription("297548",
"Schecter C-1 Hellraiser Electric Guitar",
649.95M),
new PartDescription("284704",
"Gretsch Guitars G5120 Electromatic Hollowbody Electric Guitar",
595.95M),
new PartDescription("293472",
"Rickenbacker 360 12-String Electric Guitar",
2195.95M),
new PartDescription("208476",
"Steinberger Synapse ST-2FPA TranScale Custom Electric Guitar",
1045.50M),
new PartDescription("253463",
"Gibson EDS 1275 Double-Neck Electric Guitar",
3050.25M),
new PartDescription("225747",
"Fender American Stratocaster Left-Handed Electric Guitar",
950.50M),
new PartDescription("274875",
"Epiphone Dot Studio Semi-Hollow Electric Guitar",
295.25M)
};
PartDescription[] AcousticGuitars =
{
new PartDescription("224885",
"Epiphone Hummingbird Acoustic Guitar",
245.55M),
new PartDescription("283407",
"Dean V Coustic Thin Body Acoustic-Electric Guitar",
205.50M),
new PartDescription("275111",
"Yamaha FG720S 12-String Acoustic Guitar",
325.55M),
new PartDescription("249036",
"Rogue RA-100D Dreadnought Acoustic Guitar",
82.95M),
new PartDescription("285507",
"Alvarez RD8 Regent Series Dreadnought Acoustic Guitar",
220.50M),
new PartDescription("283746",
"Epiphone EJ-200 Acoustic Guitar", 350.50M)
};
PartDescription[] ElectricBasses =
{
new PartDescription("248780",
"Epiphone Thunderbird IV Bass",
325.50M),
new PartDescription("203487",
"Squier® Vintage Modified '70s Jazz Bass",
305.95M),
new PartDescription("204633",
"Fender Standard Precision Bass",
450.75M),
new PartDescription("297548",
"Music Man StingRay 5-String Bass Guitar",
1485.95M)
};
PartDescription[] AcousElectBasses =
{
new PartDescription("248780",
"Ibanez AEB10E Acoustic-Electric Bass Guitar with Onboard Tuner",
335.50M),
new PartDescription("203487",
"Dean Playmate EABC 5-String Cutaway Acoustic-Electric Bass",
285.95M),
new PartDescription("204633",
"Fender BG-32 Acoustic/Electric Bass Guitar",
495.75M),
new PartDescription("634974",
"Gibson Thunderbird IV Bass", 1500.00M),
new PartDescription("674950",
"Rogue VB-100 Violin Bass", 255.95M),
new PartDescription("634742",
"Squier Standard P Bass 4-String Bass",
220.75M),
new PartDescription("637904",
"Peavey Millennium BXP 4-String Bass",
210.95M)
};
PartDescription[] Pianos =
{
new PartDescription("584603",
"Williams ETUDE Console Piano",
450.95M),
new PartDescription("504724",
"Rolan EP-760C Digital Piano w/Stand",
650.95M)
};
PartDescription[] Synthetizers =
{
new PartDescription("582970",
"Alesis ION 49-Key 1K DSP Synthesizer",
750.50M),
new PartDescription("524885",
"Korg MicroKORG Synthesizer/Vocoder",
350.75M),
new PartDescription("549085",
"Yamaha YDP223 Digital Piano",
1450.00M),
new PartDescription("529307",
"Access Virus kc 5-Octave Synth",
1915.55M)
};
PartDescription[] Books =
{
new PartDescription("883670",
"Alfred Guitar for the Absolute Beginner",
16.55M),
new PartDescription("837654",
"Hal Leonard Guitar Tab White Pages",
20.95M),
new PartDescription("843047",
"Carl Fischer Guitar Grimoire Progressions and Improvisation",
24.75M),
new PartDescription("845716",
"Bill Edwards Publishing Fretboard logic Spc Ed.",
17.95M),
new PartDescription("833427",
"Walrus Productions Guitar Chord Poster",
6.85M)
};
PartDescription[] Cables =
{
new PartDescription("188370",
"Musician's Friend Professional Cable",
4.55M),
new PartDescription("183614",
"Monster Cable S-100 Straight Cable",
20.95M),
new PartDescription("143047",
"Hosa TRS-TRS Stereo 1/4\" Cable",
4.65M),
new PartDescription("145716",
"Mogami Silver Series Cable",
12.95M)
};
. . . No Change
}
|
- Save all
|
Selecting an Item in a List Box |
|
To an item from a list box, the user must locate and click
the desired item. That item is said to have been selected. To programmatically select an item, you can assign the index
of the desired item to the ListBox.SelectedIndex property. The indices
of the items of a list box are stored in a zero-based array. This means that the
first item has an index of 0, the second has an index of 1, and so on. Here is
an example that will select the fourth item of the list:
private void InitializeComponent()
{
lbxFamily = new ListBox();
lbxFamily.Location = new Point(12, 12);
lbxFamily.Items.Add("Son");
lbxFamily.Items.Add("Daughter");
lbxFamily.Items.Add("Father");
lbxFamily.Items.Add("Mother");
string[] strMembers = { "Niece", "Nephew", "Uncle" };
lbxFamily.Items.AddRange(strMembers);
Controls.Add(lbxFamily);
lbxFamily.SelectedIndex = 3;
}
This would produce:
After an item has been selected, to find out the index of
the item that is currently selected, get the
value of the ListBox.SelectedIndex property.
To select an item, the user can click it in the list box. When an item has
been clicked, the list box fires a SelectedIndexChanged event. Because
selecting an item is the most regularly performed operation on a list box, SelectedIndexChanged
is the default event of a list box. This event is of type EventArgs
which means that it does not provide any significant information other than to let
you know that an item has been selected. Nonetheless, this event allows you
to easily check if an item has been selected and what item has been
selected.
To fire a SelectedIndexChanged event and to test what item has been
selected in the list, you can double-click the list box.
The ListBox.SelectedIndex property allows you either to select an
item or to find out what item is selected, using its index, that is, the
numeric position of the item in the list. If you know the identity, such as
the name, of the item you want to select, or if you want to identify the
selected item based on its name, you can use the ListBox.SelectedItem
property instead. This member identifies the item instead of locating it.
By default, the user can select only one item in the list.
If you want the user to be able to select more than one item, change the value
of the SelectionMode property. This property is based on the SelectionMode
enumeration. After the user has selected more than one item, to get the indexes
of the items that are selected, you can access the ListBox.SelectedIndices
property which holds that list.
|
Practical Learning: Selecting an Item From a List Box
|
|
- Display the form and double-click the Categories list box
- Implement its event as follows:
private void lbxCategories_SelectedIndexChanged(object sender, EventArgs e)
{
if (lbxCategories.SelectedItem == (object)"Guitars")
{
lbxTypes.Items.Add("Electric Guitars");
lbxTypes.Items.Add("Acoustic Guitars");
lbxTypes.Items.Add("Acoustic-Electric Guitars");
lbxTypes.Items.Add("Amplifiers");
lbxTypes.Items.Add("Effects");
lbxTypes.Items.Add("Microphones");
lbxTypes.Items.Add("Accessories");
lbxTypes.Items.Add("Value Packages");
}
else if (lbxCategories.SelectedItem == (object)"Bass")
lbxTypes.Items.AddRange(CatBass);
else if (lbxCategories.SelectedItem == (object)"Keyboards")
lbxTypes.Items.AddRange(CatKeyboard);
else if (lbxCategories.SelectedItem == (object)"Drums & Percussion")
lbxTypes.Items.AddRange(CatDrums);
else if (lbxCategories.SelectedItem == (object)"Band & Orchestra")
lbxTypes.Items.AddRange(CatBand);
else if (lbxCategories.SelectedItem == (object)"Books & Videos")
{
lbxTypes.Items.Add("Books");
lbxTypes.Items.Add("DVDs");
}
else if (lbxCategories.SelectedItem == (object)"Accessories")
lbxTypes.Items.AddRange(CatAccessories);
}
|
- Return to the form
- On the form, double-click the Types list box and implement its event as
follows:
private void lbxTypes_SelectedIndexChanged(object sender, EventArgs e)
{
if( lbxTypes.SelectedItem == (object)"Electric Guitars" )
foreach(PartDescription part in ElectricGuitars)
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Acoustic Guitars")
foreach(PartDescription part in AcousticGuitars )
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Electric Bass")
foreach (PartDescription part in ElectricBasses)
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Acoustic-Electric Bass")
foreach (PartDescription part in AcousElectBasses)
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Pianos")
foreach(PartDescription part in Pianos)
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Synthesizers")
foreach(PartDescription part in Synthetizers)
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Books")
foreach(PartDescription part in Books)
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Cables")
foreach(PartDescription part in Cables)
lbxItems.Items.Add(part);
}
|
- Execute the application to test it
- After using the form, close it and return to your programming environment
- On the form, click the Items list box. In the Properties window,
click the Events button
and double-click the DoubleClick field
- Implement the event as follows:
internal void CalculateTotalOrder()
{
decimal subTotal1 = 0.00M, subTotal2 = 0.00M, subTotal3 = 0.00M,
subTotal4 = 0.00M, subTotal5 = 0.00M, subTotal6 = 0.00M;
decimal orderTotal;
// Retrieve the value of each sub total
try
{
subTotal1 = decimal.Parse(this.txtSubTotal1.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
subTotal2 = decimal.Parse(this.txtSubTotal2.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
subTotal3 = decimal.Parse(this.txtSubTotal3.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
subTotal4 = decimal.Parse(this.txtSubTotal4.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
subTotal5 = decimal.Parse(this.txtSubTotal5.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
subTotal6 = decimal.Parse(this.txtSubTotal6.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
// Calculate the total value of the sub totals
orderTotal = subTotal1 + subTotal2 + subTotal3 +
subTotal4 + subTotal5 + subTotal6;
// Display the total order in the appropriate text box
this.txtTotalOrder.Text = orderTotal.ToString();
}
private void lbxItems_DoubleClick(object sender, EventArgs e)
{
// We will use a PartDescription object to identify the selected item
PartDescription part = new PartDescription();
// When the user double-clicks an item, retrieve it as
// a PartDescription object
part = (PartDescription)(lbxItems.SelectedItem);
// If the first Part # box is empty, then use it
if (txtPartID1.Text.Equals(""))
{
// Display the item number in the Part # text box
txtPartID1.Text = part.PartNumber;
// Display the name of the selected item in
// the current Description text box
txtDescription1.Text = part.PartName;
// Display the unit price of this item in
// the corresponding Unit Price text box
this.txtUnitPrice1.Text = part.UnitPrice.ToString();
// Enable the Remove button of the current item
btnRemove1.Enabled = true;
// Since an item was selected, set its quantity to 1
this.txtQuantity1.Text = "1";
// Calculate the sub total of the current item item
this.txtSubTotal1.Text = (part.UnitPrice * 1).ToString();
// Give focus to the Qty text box of the current item
this.txtQuantity1.Focus();
}// If the previous Part # text box is not empty, then use the next one
else if (this.txtPartID2.Text.Equals(""))
{
this.txtPartID2.Text = part.PartNumber;
this.txtDescription2.Text = part.PartName;
this.txtUnitPrice2.Text = part.UnitPrice.ToString();
// Enable the Remove button of the current item
btnRemove2.Enabled = true;
this.txtQuantity2.Text = "1";
this.txtSubTotal2.Text = (part.UnitPrice * 1).ToString();
this.txtQuantity2.Focus();
}
else if (this.txtPartID3.Text.Equals(""))
{
this.txtPartID3.Text = part.PartNumber;
this.txtDescription3.Text = part.PartName;
this.txtUnitPrice3.Text = part.UnitPrice.ToString();
// Enable the Remove button of the current item
btnRemove3.Enabled = true;
this.txtQuantity3.Text = "1";
this.txtSubTotal3.Text = (part.UnitPrice * 1).ToString();
this.txtQuantity3.Focus();
}
else if (this.txtPartID4.Text.Equals(""))
{
this.txtPartID4.Text = part.PartNumber;
this.txtDescription4.Text = part.PartName;
this.txtUnitPrice4.Text = part.UnitPrice.ToString();
// Enable the Remove button of the current item
btnRemove4.Enabled = true;
this.txtQuantity4.Text = "1";
this.txtSubTotal4.Text = (part.UnitPrice * 1).ToString();
this.txtQuantity4.Focus();
}
else if (this.txtPartID5.Text.Equals(""))
{
this.txtPartID5.Text = part.PartNumber;
this.txtDescription5.Text = part.PartName;
this.txtUnitPrice5.Text = part.UnitPrice.ToString();
// Enable the Remove button of the current item
btnRemove5.Enabled = true;
this.txtQuantity5.Text = "1";
this.txtSubTotal5.Text = (part.UnitPrice * 1).ToString();
this.txtQuantity5.Focus();
}
else if (this.txtPartID6.Text.Equals(""))
{
this.txtPartID6.Text = part.PartNumber;
this.txtDescription6.Text = part.PartName;
this.txtUnitPrice6.Text = part.UnitPrice.ToString();
// Enable the Remove button of the current item
btnRemove6.Enabled = true;
this.txtQuantity6.Text = "1";
this.txtSubTotal6.Text = (part.UnitPrice * 1).ToString();
this.txtQuantity6.Focus();
} // If all Part # text boxes are filled, don't do anything
else
return;
// Calculate the current total order and update the order
CalculateTotalOrder();
}
|
- Display the form and click the first text box under Unit Price
- Press and hold Shift
- Click each of the text boxes under Unit Price and each of the text boxes
under Qty
- Release Shit
- In the Properties window and in the Events section, double-click the Leave
field
- Implement the event as follows:
private void txtUnitPrice1_Leave(object sender, EventArgs e)
{
int qty1 = 0, qty2 = 0, qty3 = 0,
qty4 = 0, qty5 = 0, qty6 = 0;
decimal unitPrice1 = 0.00M, unitPrice2 = 0.00M, unitPrice3 = 0.00M,
unitPrice4 = 0.00M, unitPrice5 = 0.00M, unitPrice6 = 0.00M;
decimal subTotal1, subTotal2, subTotal3,
subTotal4, subTotal5, subTotal6;
// Get the quantity of the current item
try
{
qty1 = int.Parse(txtQuantity1.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
// Get the unit price of the current item
try
{
unitPrice1 = decimal.Parse(txtUnitPrice1.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
qty2 = int.Parse(txtQuantity2.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
unitPrice2 = decimal.Parse(txtUnitPrice2.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
qty3 = int.Parse(txtQuantity3.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
unitPrice3 = decimal.Parse(txtUnitPrice3.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
qty4 = int.Parse(txtQuantity4.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
unitPrice4 = decimal.Parse(txtUnitPrice4.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
qty5 = int.Parse(txtQuantity5.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
unitPrice5 = decimal.Parse(txtUnitPrice5.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
qty6 = int.Parse(txtQuantity6.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
try
{
unitPrice6 = decimal.Parse(txtUnitPrice6.Text);
}
catch (FormatException)
{
MessageBox.Show("Invalid Value");
}
// Calculate the sub totals
subTotal1 = qty1 * unitPrice1;
subTotal2 = qty2 * unitPrice2;
subTotal3 = qty3 * unitPrice3;
subTotal4 = qty4 * unitPrice4;
subTotal5 = qty5 * unitPrice5;
subTotal6 = qty6 * unitPrice6;
// Display the sub totals in the corresponding text boxes
txtSubTotal1.Text = subTotal1.ToString();
txtSubTotal2.Text = subTotal2.ToString();
txtSubTotal3.Text = subTotal3.ToString();
txtSubTotal4.Text = subTotal4.ToString();
txtSubTotal5.Text = subTotal5.ToString();
txtSubTotal6.Text = subTotal6.ToString();
// Update the order
CalculateTotalOrder();
}
|
- Return to the form
- Double-click the first Rmv button and implement its Click event as
follows:
private void btnRemove1_Click(object sender, EventArgs e)
{
txtPartID1.Text = "";
txtDescription1.Text = "";
txtUnitPrice1.Text = "0.00";
txtQuantity1.Text = "0";
txtSubTotal1.Text = "0.00";
btnRemove1.Enabled = false;
}
|
- Return to the form
- Double-click the second Rmv button and implement its Click event as
follows:
private void btnRemove2_Click(object sender, EventArgs e)
{
txtPartID2.Text = "";
txtDescription2.Text = "";
txtUnitPrice2.Text = "0.00";
txtQuantity2.Text = "0";
txtSubTotal2.Text = "0.00";
btnRemove2.Enabled = false;
}
|
- Return to the form
- Double-click the third Rmv button and implement its Click event as
follows:
private void btnRemove3_Click(object sender, EventArgs e)
{
txtPartID3.Text = "";
txtDescription3.Text = "";
txtUnitPrice3.Text = "0.00";
txtQuantity3.Text = "0";
txtSubTotal3.Text = "0.00";
btnRemove3.Enabled = false;
}
|
- Return to the form
- Double-click the fourth Rmv button and implement its Click event as
follows:
private void btnRemove4_Click(object sender, EventArgs e)
{
txtPartID4.Text = "";
txtDescription4.Text = "";
txtUnitPrice4.Text = "0.00";
txtQuantity4.Text = "0";
txtSubTotal4.Text = "0.00";
btnRemove4.Enabled = false;
}
|
- Return to the form
- Double-click the fifth Rmv button and implement its Click event as
follows:
private void btnRemove5_Click(object sender, EventArgs e)
{
txtPartID5.Text = "";
txtDescription5.Text = "";
txtUnitPrice5.Text = "0.00";
txtQuantity5.Text = "0";
txtSubTotal5.Text = "0.00";
btnRemove5.Enabled = false;
}
|
- Return to the form
- Double-click the sixth Rmv button and implement its Click event as
follows:
private void btnRemove6_Click(object sender, EventArgs e)
{
txtPartID6.Text = "";
txtDescription6.Text = "";
txtUnitPrice6.Text = "0.00";
txtQuantity6.Text = "0";
txtSubTotal6.Text = "0.00";
btnRemove6.Enabled = false;
}
|
- Return to the form and double-click the Close button
- Implement its Click event as follows:
private void btnClose_Click(object sender, System.EventArgs e)
{
Close();
}
|
- Execute the application to test it
|
Removing Items From a List Box |
|
If you have an undesired item in a list box, you can remove
it. To To support this operation, the ObjectCollection class provides the Remove()
method. When calling it, pass the name of the item as argument. This means that you must know
the item you are trying to delete. If you call this method, the compiler would
look for the item in the list. If the item is found, it would be deleted.
Instead of
removing an item by its name or identification, you can use its position. To do
that, you can call the RemoveAt() method and pass the zero-based index
of the undesired item. If the index is valid, the item would be deleted from the
list.
To remove all items from the list, you can call the Clear()
method.
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Practical Learning: Removing Items From a List Box
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- Change the SelectedIndex events of the Types and the Items list boxes as
follows:
private void lbxCategories_SelectedIndexChanged(object sender, EventArgs e)
{
lbxTypes.Items.Clear();
lbxItems.Items.Clear();
if (lbxCategories.SelectedItem == (object)"Guitars")
{
lbxTypes.Items.Add("Electric Guitars");
lbxTypes.Items.Add("Acoustic Guitars");
lbxTypes.Items.Add("Acoustic-Electric Guitars");
lbxTypes.Items.Add("Amplifiers");
lbxTypes.Items.Add("Effects");
lbxTypes.Items.Add("Microphones");
lbxTypes.Items.Add("Accessories");
lbxTypes.Items.Add("Value Packages");
}
else if (lbxCategories.SelectedItem == (object)"Bass")
lbxTypes.Items.AddRange(CatBass);
else if (lbxCategories.SelectedItem == (object)"Keyboards")
lbxTypes.Items.AddRange(CatKeyboard);
else if (lbxCategories.SelectedItem == (object)"Drums & Percussion")
lbxTypes.Items.AddRange(CatDrums);
else if (lbxCategories.SelectedItem == (object)"Band & Orchestra")
lbxTypes.Items.AddRange(CatBand);
else if (lbxCategories.SelectedItem == (object)"Books & Videos")
{
lbxTypes.Items.Add("Books");
lbxTypes.Items.Add("DVDs");
}
else if (lbxCategories.SelectedItem == (object)"Accessories")
lbxTypes.Items.AddRange(CatAccessories);
}
private void lbxTypes_SelectedIndexChanged(object sender, EventArgs e)
{
lbxItems.Items.Clear();
if( lbxTypes.SelectedItem == (object)"Electric Guitars" )
foreach(PartDescription part in ElectricGuitars)
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Acoustic Guitars")
foreach(PartDescription part in AcousticGuitars )
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Electric Bass")
foreach (PartDescription part in ElectricBasses)
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Acoustic-Electric Bass")
foreach (PartDescription part in AcousElectBasses)
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Pianos")
foreach(PartDescription part in Pianos)
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Synthesizers")
foreach(PartDescription part in Synthetizers)
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Books")
foreach(PartDescription part in Books)
lbxItems.Items.Add(part);
else if (lbxTypes.SelectedItem == (object)"Cables")
foreach(PartDescription part in Cables)
lbxItems.Items.Add(part);
}
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- Execute the application to test it. Here is an example:
- Close the form and return to your programming environment
After creating the list, by default, each item assumes the
position it received when it was added. If you want, you can rearrange them in
ascending order. To do this, set the ListBox.Sorted Boolean property to True.
If you create an unsorted list, then at one time get it sorted (for example, you can give the user the ability to sort the list, by clicking a button), the list would be sorted. If an item is added to the sorted list, the compiler would automatically insert
it to the right position following the alphabetical, ascending or chronological order. If at another time you allow the user to “unsort” the list, the list would keep its current order. If another item is added when the list is not sorted, the item would be positioned at the end of the list. If you want the list to have its original state, you would have to reset it through
code.
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Practical Learning: Sorting a List Box
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- On the form, click the Items list box
- In the Properties window, double-click Sorted to set its value to True
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