The ListView Project

Start a new C# or VB project. Mine is called "MovieList."

You will need to make the following changes to the main form. Figure 5-7 shows what the form should look like.

1. Size the form to be 700×450. Start-up should be Center Screen.

2. Add a Label that reads Movie genre.

3. Add a ComboBox below the Label called cmbGenre.

4. Add a Label that reads Rentals. Center the text within the Label.

5. Add a ListView control below the Rentals Label called lstRentals.

6. Add a Label that reads For Sale. Center the text within the Label.

7. Add a ListView control below the For Sale Label called lstSold.

8. Add a PictureBox called picRental.

9. Add a Label below the PictureBox that reads Rental Check Out.

Figure 5-7: A video rental form

This form is not anything that I would sell as a rental package. It is intended to show how the ListView controls work and how all of these controls can interact with each other.

What would an object-oriented program be without objects? You will need to add three additional classes to make this program work. Add the following classes to your project:

• Movie

• MovieList

• ListViewSorter

To rent movies, this program will need a Movie object. This object holds only a few items of information, such as the movie title and the rental price. A real program would need a whole host of properties. The code for this class follows.

C#

using System;

namespace MovieList_c
{
  /// <summary>
  /// Summary description for Movie.
  /// </summary>
  public class Movie
  {
    private string mName;
    private Decimal mSalePrice;
    private Decimal mRentalPrice;

    public Movie(string name)
    {
      mName = name;
      mSalePrice = 12.95m;
      mRentalPrice = 3.40m;
    }

    public string Name         { get { return mName; } }
    public Decimal SalePrice   { get { return mSalePrice; } }
    public Decimal RentalPrice { get { return mRentalPrice; } }
  }
}

VB

Option Strict On

Public Class Movie

  Private mName As String
  Private mSalePrice As Decimal
  Private mRentalPrice As Decimal

  Public Sub New(ByVal name As String)
    mName = name
    mSalePrice = 12.95D
    mRentalPrice = 3.4D
  End Sub

  Public ReadOnly Property Name() As String
    Get
      Return mName
    End Get
  End Property

  Public ReadOnly Property SalePrice() As Decimal
    Get
      Return mSalePrice
    End Get
  End Property

  Public ReadOnly Property RentalPrice() As Decimal
    Get
      Return mRentalPrice
    End Get
  End Property
End Class

Now that you have a Movie object, what do you do with it? You could put it in a collection of movies, but that would mean that at some point you would need to enumerate over that movie collection to find the one you want. This works but it requires code.

In thinking about the design of this example, I knew that I would be working with ListViewItems as my major object. After all, I have two ListView controls that work only with ListViewItems as objects. A ListViewItems has a Tag property. This Tag property was designed to hold an object whose data relates to the ListViewItem. In the case of this example, I store the Movie object in the ListViewItem.Tag property of each record shown in the ListView control. This gives me direct access to the movie in question without having to search through some unrelated collection.

The next class to fill in is the MovieList class. This class does several things. The basis of the class is the same as the class I showed you in the previous example; it is designed to hold a collection of ListViewItem objects. I have added the following functionality to this class:

• Gets its data from a text file in the current directory

• Parses each line of the text file into a ListViewItem with associated subitems

• Instantiates a Movie object for each ListViewItem and saves it in the ListViewItem.Tag property

• Removes a ListViewItem from the collection

• Changes a property of a single ListViewItem in the collection

The code in Listings 5-2a and 5-2b show this MovieList class. Read the code carefully to see what I am doing.

Listing 5-2a: C# Code for the MovieList Class

using System;
using System.IO;
using System.Collections;
using System.Windows.Forms;

namespace MovieList_c
{
  /// <summary>
  /// Summary description for MovieList.
  /// </summary>
  public class MovieList
  {
    private const string OUT = "Out";
    private const string INHOUSE = "In";

    private ArrayList mCol;
    private char      mDelimiter = '^';
    private string    mGenre;

    public MovieList()
    {
      mCol = new ArrayList();
    }

    public MovieList(string fname)
    {
      string buffer;
      mCol = new ArrayList();
      FileInfo fIn = new FileInfo(fname);
      try
      {
        StreamReader sr = new StreamReader( fIn.OpenRead() );
        while (sr.Peek() != -1)
        {
          buffer = sr.ReadLine();
          string[] List = buffer.Split(mDelimiter);
          if(List.GetLength(0) == 1)
          {
            if(buffer != string.Empty)
            mGenre = buffer;
          }
          else if(List.GetLength(0) > 1)
          {
            ListViewItem l = new ListViewItem(List);
            l.Tag = new Movie(l.Text);
            mCol.Add(l);
          }
        }
        sr.Close();
      }
      catch(Exception e)
      {
        MessageBox.Show("Unable to read file " + fname);
        throw e;
      }
    }

    public override string ToString() { return mGenre; }
    public string Genre { get{return mGenre;} }

    /// <summary>
    /// Add a string to an array of ListViewItems
    /// </summary>
    /// <param name="val"></param>
    public void Add(string val)
    {
      mCol.Add(new ListViewItem(val));
    }

    /// <summary>
    /// Add a ListViewItem to an array of ListViewItems
    /// </summary>
    /// <param name="val"></param>
    public void Add(ListViewItem val)
    {
      mCol.Add(val);
    }

    /// <summary>
    /// Remove a ListViewItem from the array of ListViewItems
    /// </summary>
    /// <param name="val"></param>
    public void Remove(ListViewItem val)
    {
      mCol.Remove(val);
    }

    /// <summary>
    /// Checkout a movie
    /// </summary>
    /// <param name="val"></param>
    public bool CheckOut(ListViewItem val)
    {
      string stock = val.SubItems[val.SubItems.Count-1].Text;

      if(stock == OUT)
        return false;

      mCol.Remove(val);
      val.SubItems[val.SubItems.Count-1].Text = OUT;
      mCol.Add(val);
      return true;
    }

    /// <summary>
    /// Gets a ListViewItem array
    /// </summary>
    public ListViewItem[] Items
    {
      get
      {
        mCol.TrimToSize();
        ListViewItem[] lvw = new ListViewItem[mCol.Count];
        mCol.CopyTo(lvw, 0);
        return lvw;
      }
    }
  }
}

Listing 5-2b: VB Code for the MovieList Class

Option Strict On

Imports System
Imports System.IO
Imports System.Collections
Imports System.Windows.Forms

Public Class MovieList

  Private Const OUT As String = "Out"
  Private Const INHOUSE As String = "In"

  Private mCol As ArrayList
  Private mDelimiter As Char = "^"c
  Private mGenre As String

  Public Sub New()
    mCol = New ArrayList()
  End Sub

  Public Sub New(ByVal fname As String)
    Dim buffer As String

    mCol = New ArrayList()
    Dim fIn As FileInfo = New FileInfo(fname)
    Try
      Dim sr As StreamReader = New StreamReader(fIn.OpenRead())
      While (sr.Peek() <> -1)
        buffer = sr.ReadLine()
        Dim List() As String = buffer.Split(mDelimiter)
        If List.GetLength(0) = 1 Then
          If (buffer <> String.Empty) Then
            mGenre = buffer
          End If
        ElseIf List.GetLength(0) > 1 Then
          Dim l As ListViewItem = New ListViewItem(List)
          l.Tag = New Movie(l.Text)
          mCol.Add(l)
        End If
      End While
      sr.Close()
    Catch e As Exception
      MessageBox.Show("Unable to read file " + fname)
      Throw e
    End Try
  End Sub

  Public Overrides Function ToString() As String
    Return mGenre
  End Function

  Public ReadOnly Property Genre() As String
    Get
      Return mGenre
    End Get
  End Property

  Public Sub Add(ByVal val As String)
    mCol.Add(New ListViewItem(val))
  End Sub

  Public Sub Add(ByVal val As ListViewItem)
    mCol.Add(val)
  End Sub

  Public Sub Remove(ByVal val As ListViewItem)
    mCol.Remove(val)
  End Sub

  Public Function CheckOut(ByVal val As ListViewItem) As Boolean
    Dim stock As String = val.SubItems(val.SubItems.Count - 1).Text

    If stock = OUT Then
      Return False
    End If

    mCol.Remove(val)
    val.SubItems(val.SubItems.Count - 1).Text = OUT
    mCol.Add(val)
    Return True
  End Function

  Public ReadOnly Property Items() As ListViewItem()
    Get
      mCol.TrimToSize()
      Dim lvw(mCol.Count) As ListViewItem
      mCol.CopyTo(lvw, 0)
      Return lvw
    End Get
  End Property

End Class

Let's dissect this class a little. Look at the constructor. Inside of a Try-Catch block I open a text file, read it in line by line, and create ListItems from the contents of each line. Here is the relevant C# code:

        StreamReader sr = new StreamReader( fIn.OpenRead() );
        while (sr.Peek() != -1)
        {
          buffer = sr.ReadLine();
          string[] List = buffer.Split(mDelimiter);
          if(List.GetLength(0) == 1)
          {
            if(buffer != string.Empty)
              mGenre = buffer;
          }
          else if(List.GetLength(0) > 1)
          {
            ListViewItem l = new ListViewItem(List);
            l.Tag = new Movie(l.Text);
            mCol.Add(l);
          }
        }

At the top of this file I declared a delimiter constant to be the caret symbol. If you look through the file, you will see that each line uses this symbol for a delimiter. Here is the ActionMovie.txt file:

Action Movies

StageCoach^1932^94^VHS^In
Speed^1994^120^8mm^Out
Alien^1986^98^DVD^In
Train Robber^1923^36^VHS^In

The first line of this file is the genre of movies. The code detects this because there are no delimiters in this line. The other four lines are delimited records. As each one is read in, I create an array of strings to represent each field in the record. I then add each array en masse to the constructor of the ListViewItem class, which automatically creates a ListViewItem and as many ListViewSubItem objects as needed. This ListViewItem is then added to the total collection. The first line I read in gets assigned to the Genre variable.

There is one other line of code in this class that I would like to draw your attention to. Here is the C# code:

    public override string ToString() { return mGenre; }

Would you believe me if I told you that without this line of code, the whole program would not work as it does? You will learn the reason for this in a bit. For now, see the sidebar "Overriding the ToString() Method" for an explanation.

I will leave the third class, ListViewSorter, for a bit later.

Overriding the ToString() Method

I use a ComboBox in the main form to choose the genre of movie that should be displayed in the movie list. Bring up the help file for the ComboBox and you will see that it allows you to add only an object to its item list. The only kind of code I have ever seen with a ComboBox loads a string as an item is something like this:

    ComboBox cmb = new ComboBox();
    cmb.Items.Add("First Choice");
    cmb.Items.Add("Second Choice");
    cmb.Items.Add("Third Choice");

If the programmer needs to know what item was chosen, he or she looks at the selected index property and does something based on that. Perhaps the programmer even compares the text property to some lookup table and performs an action based on the index of the lookup. Although this kind of code works, it is not what the authors of this control intended.

Read the help carefully for the Add function of this control. It says that the string displayed is the object's ToString() method. Suppose you add a bunch of PictureBoxes to this list like so:

    ComboBox cmb = new ComboBox();
    cmb.Items.Add(new PictureBox());
    cmb.Items.Add(new PictureBox());
    cmb.Items.Add(new PictureBox());

This is perfectly valid code. If you look at the result, you see a ComboBox that has the following entries:

System.Windows.Forms.PictureBox
System.Windows.Forms.PictureBox
System.Windows.Forms.PictureBox

What you see is the text you get from the PictureBox.ToString() method. Now in the case of this example, I created a class that overrides the ToString() method that returns the genre of the movie list. Normally, it would have returned the name of the class. When I add instances of this class (objects) to the ComboBox list, the ComboBox will get the displayed text from the ToString() method and will look to the user as if I entered in strings only.

Adding the object directly to the Item list of the ComboBox allows me to get the SelectedItem, cast it to the proper data type, and then call a method directly. There is no lookup involved. In fact, my program does not even know, or keep track of, what or how many objects are in the ComboBox. This is way cool!

The Main Movie Form Code

You have the supporting guts of this project done. Now it is time to add the code for the main form. Start out with some class local variables.

C#

    #region class local variables

    MovieList ActionMovies;
    MovieList DramaMovies;
    MovieList ComedyMovies;
    ImageList BigIcons;

    #endregion

VB

#Region "class local variables"

  Private ActionMovies As MovieList
  Private DramaMovies As MovieList
  Private ComedyMovies As MovieList
  Private BigIcons As ImageList

#End Region

As you can see, I have three types of movies. I also have an ImageList that I use for the icon display ListView control. Before I add any constructor code I will need some delegates to call. The mouse does a lot of work in this program, so I have quite a few mouse event handlers. Most of them are used for drag-and-drop operations.

C#

    #region Delegates

    private void GenreClick(object sender, EventArgs e)
    {
      ComboBox cmb = (ComboBox)sender;
      GetList((MovieList)cmb.SelectedItem);
    }

    private void MovieRentalStartDrag(object sender, ItemDragEventArgs e)
    {
      lstRentals.DoDragDrop(e.Item, DragDropEffects.Move);
    }

    private void MovieRentalDragAcross(object sender, DragEventArgs e)
    {
      e.Effect = DragDropEffects.Move;
    }

    private void MovieDragInto(object sender, DragEventArgs e)
    {
      //The data must come from the lstRentals ListView
      object o = e.Data.GetData(DataFormats.Serializable);
      if(o is ListViewItem)
      {
        ListViewItem l = (ListViewItem)o;
        if (l.ListView == lstRentals)
          e.Effect = DragDropEffects.All;
        else
          e.Effect = DragDropEffects.None;
      }
    }
    private void RentalCartDrop(object sender, DragEventArgs e)
    {
      object o = e.Data.GetData(DataFormats.Serializable);
      ListViewItem l = (ListViewItem)o;

      DialogResult dr = MessageBox.Show("Confirm Rental of " + l.Text,
                                        "Rent Video",
                                        MessageBoxButtons.YesNo);
      if(dr == DialogResult.No)
        return;

      //Look at the genre combo box to see which movie list to delete this
      //ListViewItem from.
      MovieList m = (MovieList)cmbGenre.SelectedItem;
      if(!m.CheckOut(l))
        MessageBox.Show("This Movie is already out.");

    }

    private void MovieSoldDrop(object sender, DragEventArgs e)
    {
      object o = e.Data.GetData(DataFormats.Serializable);
      ListViewItem l = (ListViewItem)o;

      DialogResult dr = MessageBox.Show("Are you sure you want to sell " +
                                        l.Text + "?" ,
                                        "Sell This Video",
                                        MessageBoxButtons.YesNo);

      if(dr == DialogResult.No)
        return;

      //Very important!! If I did not remove this ListViewItem from the source
      //list I would need to clone this ListViewItem before I add it to the
      //lstSold control.
      lstRentals.Items.Remove(l);
      lstSold.Items.Add((ListViewItem)l);
      lstSold.Items[lstSold.Items.Count-1].ImageIndex = 0;
      //Look at the genre combo box to see which movie list to delete this
      //ListViewItem from.
      MovieList m = (MovieList)cmbGenre.SelectedItem;
      m.Remove(l);

    }

    #endregion

VB

#Region "Delegates"

  Private Sub GenreClick(ByVal sender As Object, ByVal e As EventArgs)
    Dim cmb As ComboBox = CType(sender, ComboBox)
    GetList(CType(cmb.SelectedItem, MovieList))
  End Sub

  Private Sub MovieRentalStartDrag(ByVal sender As Object, _
                                   ByVal e As ItemDragEventArgs)
    lstRentals.DoDragDrop(e.Item, DragDropEffects.Move)
  End Sub

  Private Sub MovieRentalDragAcross(ByVal sender As Object, _
                                    ByVal e As DragEventArgs)
    e.Effect = DragDropEffects.Move
  End Sub

  Private Sub MovieDragInto(ByVal sender As Object, ByVal e As DragEventArgs)
    'The data must come from the lstRentals ListView
    Dim o As Object = e.Data.GetData(DataFormats.Serializable)
    If o.GetType() Is GetType(ListViewItem) Then
      Dim l As ListViewItem = DirectCast(o, ListViewItem)
      If (l.ListView Is lstRentals) Then
        e.Effect = DragDropEffects.All
      Else
        e.Effect = DragDropEffects.None
      End If
    End If
  End Sub

  Private Sub RentalCartDrop(ByVal sender As Object, ByVal e As DragEventArgs)
    Dim o As Object = e.Data.GetData(DataFormats.Serializable)
    Dim l As ListViewItem = DirectCast(o, ListViewItem)

    Dim dr As DialogResult = MessageBox.Show("Confirm Rental of " + l.Text, _
                                      "Rent Video", _
                                      MessageBoxButtons.YesNo)

    If dr = DialogResult.No Then
      Return
    End If

    'Look at the genre combo box to see which movie list to delete this
    'ListViewItem from.
    Dim m As MovieList = CType(cmbGenre.SelectedItem, MovieList)
    If Not m.CheckOut(l) Then
      MessageBox.Show("This Movie is already out.")
    End If
  End Sub

  Private Sub MovieSoldDrop(ByVal sender As Object, ByVal e As DragEventArgs)
    Dim o As Object = e.Data.GetData(DataFormats.Serializable)
    Dim l As ListViewItem = DirectCast(o, ListViewItem)

    Dim dr As DialogResult = MessageBox.Show("Are you sure you want to sell " + _
                                      l.Text + "?", _
                                      "Sell This Video", _
                                      MessageBoxButtons.YesNo)

    If dr = DialogResult.No Then
      Return
    End If

    'Very important!! If I did not remove this ListViewItem from the source
    'list I would need to clone this ListViewItem before I add it to the
    'lstSold control.
    lstRentals.Items.Remove(l)
    lstSold.Items.Add(DirectCast(l, ListViewItem))
    lstSold.Items(lstSold.Items.Count - 1).ImageIndex = 0
    'Look at the genre combo box to see which movie list to delete this
    'ListViewItem from.
    Dim m As MovieList = CType(cmbGenre.SelectedItem, MovieList)
    m.Remove(l)

  End Sub

#End Region

Most of these delegates take care of the housekeeping during drag-and-drop operations.

The GenreClick method calls GetList. This helper function follows.

C#

    private void GetList(MovieList list)
    {
      lstRentals.BeginUpdate();
      lstRentals.Items.Clear();
      lstRentals.Items.AddRange(list.Items);
      lstRentals.EndUpdate();
    }

VB

  Private Sub GetList(ByVal list As MovieList)
    lstRentals.BeginUpdate()
    lstRentals.Items.Clear()
    lstRentals.Items.AddRange(list.Items)
    lstRentals.EndUpdate()
  End Sub

Several things need to happen for a drag-and-drop operation to work:

• The source object must be serializable. Most .NET objects are, but if you want to drag and drop your own object, it must inherit from the ISerializable interface.

• You must hook to an event (usually MouseDown) where you use the DoDrag method. This method needs the object being dragged and the DragEffects enumeration you want. Note that the ListView has a special ItemDrag event that I use here to start the process.

• You must set up the receiving control to allow drop operations. You do this with the AllowDrop property.

• Hook up to the DragEnter event for the destination control. Here you will detect the object being dragged and either allow the operation to continue or deny it.

• Hook up to the DragDrop event in the destination control and perform whatever operation is needed with the data from the source object.

You can hook into some other events with drag and drop, but the preceding list covers the basics.

Along the way, you need to know a couple of things. First, you need to know that the DragEffects enumeration allows you to specify if you want the operation to be a copy, move, or cancelled. If you use DragEffects.None, you will effectively cancel the drag operation.

Second, you need to know how to get the data that you are transferring over. There are a few standard data types that the drag-and-drop operation knows about. These types are the most common types of data to be moved. Some of the data types are as follows:

• Bitmap

• CSV format text

• HTML

• Text

You should be aware of a whole host of other data types. See the online help for the DataFormats class. If your object does not fall into one of these nice categories, then you will need to use DataFormats.Serializable like I did. This returns an object that you will need to cast to the proper data type before you can use it.

Note that in the MovieSoldDrop event, I remove the ListViewItem object from its source ListView control before I add it to the destination ListView control. I need to do this because common sense dictates that it should only be in one bin at a time. Also, I need to do this because the object can be in only one ListView control at a time. If I want it in both, I need to clone the ListViewItem before I add it to the second control.

The last thing I do in the drag-and-drop operation here is to remove the ListViewItem object from its MovieList collection. Now, as I change genres using the ComboBox, I will not see this movie again when I reload its genre collection.

If you ran the program now, nothing would happen. Although this seems to happen all too often with released code, at least you can say you know something was left out here. You will need to fill in the constructor with initialization code.

Listings 5-3a and 5-3b show the code for the constructor. Note that I am doing a little exception handling in here as far as reading in the movie files go.

Listing 5-3a: C# Constructor Initialization Code

    public Form1()
    {
      InitializeComponent();

      //Get the movie ListViewItems
      try   { ActionMovies = new MovieList("ActionMovies.txt"); }
      catch { ActionMovies = null; }

      try   { DramaMovies = new MovieList("DramaMovies.txt"); }
      catch { DramaMovies = null; }

      try   { ComedyMovies = new MovieList("ComedyMovies.txt"); }
      catch { ComedyMovies = null; }

      //Set up the rental ListView
      lstRentals.View = View.Details;
      lstRentals.AllowColumnReorder = true;
      lstRentals.GridLines = true;
      lstRentals.FullRowSelect = true;
      lstRentals.AllowDrop = true;
      lstRentals.ItemDrag += new
           ItemDragEventHandler
          (this.MovieRentalStartDrag);
      lstRentals.DragEnter += new
          DragEventHandler
          (this.MovieRentalDragAcross);
      lstRentals.Columns.Add("Title",        -2, HorizontalAlignment.Center);
      lstRentals.Columns.Add("Release Date", -2, HorizontalAlignment.Center);
      lstRentals.Columns.Add("Running Time", -2, HorizontalAlignment.Center);
      lstRentals.Columns.Add("Format",       -2, HorizontalAlignment.Center);
      lstRentals.Columns.Add("In Stock",     -2, HorizontalAlignment.Center);

      //Now set up the For-Sale ListView
      BigIcons = new ImageList();
      BigIcons.Images.Add(Image.FromFile("movie.bmp"));
      lstSold.LargeImageList = BigIcons;
      lstSold.View = View.LargeIcon;
      lstSold.AllowDrop = true;
      lstSold.DragEnter += new DragEventHandler(MovieDragInto);
      lstSold.DragDrop += new DragEventHandler(MovieSoldDrop);

      //Fill the rental box
      picRental.SizeMode = PictureBoxSizeMode.StretchImage;
      picRental.Image = Image.FromFile("cart.bmp");
      picRental.AllowDrop = true;
      picRental.DragEnter += new DragEventHandler(MovieDragInto);
      picRental.DragDrop += new DragEventHandler(this.RentalCartDrop);

      //Fill the ComboBox. This MUST be done after setting up the
      //rental listView control
      if(ActionMovies != null) cmbGenre.Items.Add(ActionMovies);
      if(DramaMovies != null) cmbGenre.Items.Add(DramaMovies);
      if(ComedyMovies != null) cmbGenre.Items.Add(ComedyMovies);
      cmbGenre.SelectedIndexChanged += new EventHandler(this.GenreClick);
      //Setting the index automatically fires the event
      cmbGenre.SelectedIndex = 0;
    }

Listing 5-3b: VB Constructor Initialization Code

  Public Sub New()
    MyBase.New()

    'This call is required by the Windows Form Designer.
    InitializeComponent()

    'Get the movie ListViewItems
    Try
      ActionMovies = New MovieList("ActionMovies.txt")
    Catch
      ActionMovies = Nothing
    End Try
    Try
      DramaMovies = New MovieList("DramaMovies.txt")
    Catch
      DramaMovies = Nothing
    End Try

    Try
      ComedyMovies = New MovieList("ComedyMovies.txt")
    Catch
      ComedyMovies = Nothing
    End Try

    'Set up the rental ListView
    lstRentals.View = View.Details
    lstRentals.AllowColumnReorder = True
    lstRentals.GridLines = True
    lstRentals.FullRowSelect = True
    lstRentals.AllowDrop = True
    AddHandler lstRentals.ItemDrag, New ItemDragEventHandler _
                                        (AddressOf MovieRentalStartDrag)
    AddHandler lstRentals.DragEnter, New DragEventHandler _
                                        (AddressOf MovieRentalDragAcross)

    lstRentals.Columns.Add("Title", -2, HorizontalAlignment.Center)
    lstRentals.Columns.Add("Release Date", -2, HorizontalAlignment.Center)
    lstRentals.Columns.Add("Running Time", -2, HorizontalAlignment.Center)
    lstRentals.Columns.Add("Format", -2, HorizontalAlignment.Center)
    lstRentals.Columns.Add("In Stock", -2, HorizontalAlignment.Center)

    'Now set up the For-Sale ListView
    BigIcons = New ImageList()
    BigIcons.Images.Add(Image.FromFile("movie.bmp"))
    lstSold.LargeImageList = BigIcons
    lstSold.View = View.LargeIcon
    lstSold.AllowDrop = True
    AddHandler lstSold.DragEnter, New DragEventHandler(AddressOf MovieDragInto)
    AddHandler lstSold.DragDrop, New DragEventHandler(AddressOf MovieSoldDrop)

    'Fill the rental box
    picRental.SizeMode = PictureBoxSizeMode.StretchImage
    picRental.Image = Image.FromFile("cart.bmp")
    picRental.AllowDrop = True
    AddHandler picRental.DragEnter, New DragEventHandler(AddressOf MovieDragInto)
    AddHandler picRental.DragDrop, New DragEventHandler(AddressOf RentalCartDrop)
    'Fill the ComboBox. This MUST be done after setting up the
    'rental listView control
    If Not ActionMovies Is Nothing Then cmbGenre.Items.Add(ActionMovies)
    If Not DramaMovies Is Nothing Then cmbGenre.Items.Add(DramaMovies)
    If Not ComedyMovies Is Nothing Then cmbGenre.Items.Add(ComedyMovies)
    AddHandler cmbGenre.SelectedIndexChanged, New EventHandler _
                                                  (AddressOf GenreClick)
    'Setting the index automatically fires the event
    cmbGenre.SelectedIndex = 0

  End Sub

Let's look at what's going on here. First, I initialize three MovieList objects. If the objects fail to initialize properly, I set these objects to null. By doing this, I allow the program to run correctly with only one or two valid MovieLists. The most likely reason for a MovieList object failing to initialize properly is an inability to read the text file.

After this, I initialize the two ListView controls and I put a picture of a shopping cart in the PictureBox control. Notice that I set up this PictureBox for drag-and-drop operations as well. The last thing I do in this constructor is fill the ComboBox. Here is the code again:

        //Fill the ComboBox. This MUST be done after setting up the
        //rental listView control
        if(ActionMovies != null) cmbGenre.Items.Add(ActionMovies);
        if(DramaMovies != null) cmbGenre.Items.Add(DramaMovies);
        if(ComedyMovies != null) cmbGenre.Items.Add(ComedyMovies);
        cmbGenre.SelectedIndexChanged += new EventHandler(this.GenreClick);
        //Setting the index automatically fires the event
        cmbGenre.SelectedIndex = 0;

If the MovieList object is not null (nothing in VB) I add the object to the ComboBox. Remember how I overrode the ToString() method in the MovieList class? The ComboBox gets the text to display from the ToString method of the object that I add.

Once I set the event handler, I set the SelectedIndex property to the first item. Doing this programmatically automatically calls the delegate for the event handler. This is why this operation is left until last. If I did it before finishing the setup, I would have bugs galore.

Run the program and play with it. Figure 5-8 shows this form as it is running.

Figure 5-8: Running the video rental form

This form does everything you would expect it to, with perhaps a few exceptions. You are not able to reverse a checkout and you are not able to put a movie from the For Sale bin back into the Rentals bin. You have enough knowledge to do this yourself if you are so inclined.

Play around with the Rentals ListView. You are able to swap columns. You are not able to sort them, though. Sorting columns is a common thing in this kind of control and your users will expect it.

You can set up sorting by hooking into the ColumnClick event and reversing the current sort order. This allows you to click a column and go from a descending sort to an ascending sort. The problem with this is that it sorts only on the first column. I know that when I come across ListViews like this, I expect to click any column and have the list sorted according to that column. This last piece of code accomplishes this.

Remember the ListViewSorter class I had you make? I bet you forgot all about that. Currently it has no code in it. What follows is the code for this class.

C#

using System;
using System.Windows.Forms;
using System.Collections;

namespace MovieList_c
{
  /// <summary>
  /// This class sorts a ListView control by column
  /// </summary>
  public class ListViewSorter: IComparer
  {
    private int mCol;
    private SortOrder mOrder;

    public ListViewSorter(int column, SortOrder order)
    {
      mCol=column;
      mOrder = order;
    }
    public int Compare(object x, object y)
    {
      int returnVal = String.Compare(((ListViewItem)x).SubItems[mCol].Text,
        ((ListViewItem)y).SubItems[mCol].Text);
      if(mOrder == SortOrder.Descending)
        return (returnVal *= -1);
      else
        return returnVal;
    }
  }
}

VB

Option Strict On

Imports System.Windows.Forms
Imports System.Collections

Public Class ListViewSorter
  Implements IComparer
  Dim mCol As Integer
  Dim mOrder As SortOrder

  Public Sub New(ByVal column As Integer, ByVal order As SortOrder)
    mCol = column
    mOrder = order
  End Sub

  Public Function Compare(ByVal x As Object, ByVal y As Object) As Integer _
                          Implements System.Collections.IComparer.Compare
    Dim returnVal As Integer = String.Compare( _
                                (CType(x, ListViewItem)).SubItems(mCol).Text, _
                                (CType(y, ListViewItem).SubItems(mCol).Text))
    If mOrder = SortOrder.Descending Then
      returnVal *= -1
      Return returnVal
    Else
      Return returnVal
    End If
  End Function

End Class

This class allows you to override the normal compare routine of the ListView. Add the following delegate to the main form.

C#

    private void ColumnSort(object sender, ColumnClickEventArgs e)
    {
      ListView lvw = (ListView)sender;
      ArrayList SortList = (ArrayList)lvw.Tag;
      SortList[e.Column] = (SortOrder)SortList[e.Column] ==
                           SortOrder.Ascending ?
                           SortOrder.Descending :
                           SortOrder.Ascending;
      lvw.Sorting = (SortOrder)SortList[e.Column];

      lvw.BeginUpdate();
      lvw.ListViewItemSorter = new ListViewSorter(e.Column, lvw.Sorting);
      lvw.Sort();
      lvw.EndUpdate();
    }

VB

  Private Sub ColumnSort(ByVal sender As Object, ByVal e As ColumnClickEventArgs)
    Dim lvw As ListView = CType(sender, ListView)
    Dim SortList As ArrayList = CType(lvw.Tag, ArrayList)
    SortList(e.Column) = IIf(DirectCast(SortList(e.Column), SortOrder) = _
                                                     SortOrder.Ascending, _
                                                     SortOrder.Descending, _
                                                     SortOrder.Ascending)
    lvw.Sorting = DirectCast(SortList(e.Column), SortOrder)

    lvw.BeginUpdate()
    lvw.ListViewItemSorter = New ListViewSorter(e.Column, lvw.Sorting)
    lvw.Sort()
    lvw.EndUpdate()
  End Sub

What I have here is an array of sort orders for each column in the ListView. Depending on which column you select, this method gets the last sort order for that column and changes it to the opposite order. It then redirects the ListViewItemSorter property to use the ListViewSorter class, which sorts the ListView based on the column and sort order passed in. Notice that the sort order array was retrieved from the Tag property of the ListView control.

To make this all work, add the following code to the constructor just below where you initialized the lstRentals ListView control.

C#

    ArrayList order = new ArrayList();
    for(int k=0; k<lstRentals.Columns.Count; k++)
      order.Insert(k, SortOrder.Ascending);
    order.TrimToSize();
    lstRentals.Tag = order;
    lstRentals.ColumnClick += new ColumnClickEventHandler(ColumnSort);

VB

    'Make something that will hold the current sort order for the current column
    Dim order As ArrayList = New ArrayList()
    Dim k As Integer
    For k = 0 To lstRentals.Columns.Count - 1
      order.Insert(k, SortOrder.Ascending)
    Next
    order.TrimToSize()
    lstRentals.Tag = order
    AddHandler lstRentals.ColumnClick, New ColumnClickEventHandler _
                                            (AddressOf ColumnSort)

Notice that I keep the sort order array as a part of the ListView control. Doing this obviates the need for me to keep any global variables, and it also eliminates the need to keep track of which array belongs to which ListView control. The ColumnSort delegate does not care which ListView control needs sorting, nor does it care how many columns that control has.

Now you can run the program and click different columns in the lstRentals ListView control. You will be able to sort in ascending or descending order based on the column that you clicked. This functionality is not just a nicety in data entry programs; it is required.

One note here. Click the column header for the running time. See that the sort order is 98, 94, 36, 120 for descending and the reverse for ascending. How can this be? Take a piece of paper and the ASCII chart and compare the text representations of these numbers. You will see that the order is correct (120 begins with a 1 so its sort order is first).

What to do? In order to fix things like this, you will need to make a compare routine for each column. If you have a column of numbers, you will need to sort according to numerical order.