Cómo: Crear un cuadro de lista dibujado por el propietario

Artículo
10/07/2008

Actualización: noviembre 2007

Se puede crear un cuadro de lista dibujado por el propietario con .NET Compact Framework, aunque no tan fácilmente como con .NET Framework completo. .NET Compact Framework no admite DrawMode, DrawItem y otros miembros de dibujo para un cuadro de lista y otros controles, pero se puede programar esa funcionalidad. En este ejemplo se proporciona una clase de control personalizada para crear un cuadro de lista dibujado por el propietario, y se implementa el control como un cuadro de lista para seleccionar las fuentes.

Este ejemplo contiene una clase base, OwnerDrawnListBox, de la que se deriva FontListBox. Entre las funciones básicas de OwnerDrawnListBox se incluyen las siguientes:

Proporciona la barra de desplazamiento vertical, una matriz para contener los elementos, y un mapa de bits para crear el cuadro de lista.
Proporciona una propiedad de alto de elemento y determina cuántos elementos se pueden dibujar para un alto determinado del control.
Proporciona una propiedad SelectedIndex que determina el elemento seleccionado mediante la barra de desplazamiento actual, el alto del elemento y los valores de las coordenadas del puntero del mouse.
Proporciona un evento SelectedIndexChanged.
Garantiza la visibilidad de los elementos.
Quita la barra de desplazamiento, si no se necesita.
Proporciona la operación del teclado con las teclas de navegación hacia arriba y hacia abajo.

La clase FontListBox hereda de OwnerDrawnListBox. Entre las implementaciones y técnicas se incluyen las siguientes:

Determina el alto correcto del elemento.
Dibuja los elementos, con el elemento seleccionado dibujado en forma resaltada, utilizando un método OnPaint reemplazado. Para evitar el parpadeo, este método no muestra el control hasta que están dibujadas todas sus características gráficas.
Proporciona la propiedad SelectedFaceName, que contiene el nombre de la fuente seleccionada.

El formulario, DrawFontList, realiza las acciones siguientes:

Crea una nueva instancia de FontListBox y la agrega a la colección de controles.
Agrega un controlador de eventos para el evento SelectedIndexChanged.
Rellena FontListBox con una lista de fuentes.
Proporciona etiquetas para que se muestre el ejemplo de la fuente seleccionada.

Para crear un cuadro de lista dibujado por el propietario

Agregue el control OwnerDrawnListBox personalizado al proyecto.

' Base custom control for DrawFontList
Class OwnerDrawnListBox
    Inherits Control
    Private Const SCROLL_WIDTH As Integer = 20
    Private itemH As Integer = -1
    Private selIndex As Integer = -1

    Private offScreenBitmap As Bitmap
    Private vs As VScrollBar
    Private itemsAList As ArrayList


    Public Sub New()
        Me.vs = New VScrollBar
        Me.vs.Parent = Me
        Me.vs.Visible = False
        Me.vs.SmallChange = 1
        AddHandler Me.vs.ValueChanged, AddressOf Me.ScrollValueChanged

        Me.itemsAList = New ArrayList
    End Sub


    Public ReadOnly Property Items() As ArrayList
        Get
            Return Me.itemsAList
        End Get
    End Property


    Protected ReadOnly Property OffScreen() As Bitmap
        Get
            Return Me.offScreenBitmap
        End Get
    End Property


    Protected ReadOnly Property VScrollBar() As VScrollBar
        Get
            Return Me.vs
        End Get
    End Property

    Friend Event SelectedIndexChanged As EventHandler


    Protected Overridable Sub OnSelectedIndexChanged(ByVal e As EventArgs)
        RaiseEvent SelectedIndexChanged(Me, e)
    End Sub

    Protected Overrides Sub OnMouseDown(ByVal e As MouseEventArgs)
        Me.SelectedIndex = Me.vs.Value + e.Y / Me.ItemHeight

        ' Invalidate the control so we can draw the item as selected.
        Me.Refresh()
    End Sub

    ' Get or set index of selected item.
    Public Property SelectedIndex() As Integer
        Get
            Return Me.selIndex
        End Get

        Set(ByVal Value As Integer)
            Me.selIndex = Value

            RaiseEvent SelectedIndexChanged(Me, Nothing)
        End Set
    End Property


    Protected Sub ScrollValueChanged(ByVal o As Object, ByVal e As EventArgs)
        Me.Refresh()
    End Sub


    Protected Overridable Property ItemHeight() As Integer
        Get
            Return Me.itemH
        End Get

        Set(ByVal Value As Integer)
            Me.itemH = Value
        End Set
    End Property


    ' If the requested index is before the first visible index then set the
    ' first item to be the requested index. If it is after the last visible
    ' index, then set the last visible index to be the requested index.
    Public Sub EnsureVisible(ByVal index As Integer)
        If index < Me.vs.Value Then
            Me.vs.Value = index
            Me.Refresh()
        ElseIf index >= Me.vs.Value + Me.DrawCount Then
            Me.vs.Value = index - Me.DrawCount + 1
            Me.Refresh()
        End If
    End Sub


    ' Need to set focus to the control when it 
    ' is clicked so that keyboard events occur.
    Protected Overrides Sub OnClick(ByVal e As EventArgs)
        Me.Focus()
        MyBase.OnClick(e)
    End Sub

    ' Selected item moves when you use the keyboard up/down keys.
    Protected Overrides Sub OnKeyDown(ByVal e As KeyEventArgs)
        Select Case e.KeyCode
            Case Keys.Down
                If Me.SelectedIndex < Me.vs.Maximum Then
                    Me.SelectedIndex = Me.SelectedIndex + 1
                    EnsureVisible(Me.SelectedIndex + 1)
                    Me.Refresh()
                End If
            Case Keys.Up
                If Me.SelectedIndex > Me.vs.Minimum Then
                    Me.SelectedIndex = Me.SelectedIndex - 1
                    EnsureVisible(Me.SelectedIndex - 1)
                    Me.Refresh()
                End If
            Case Keys.PageDown
                Me.SelectedIndex = Math.Min(Me.vs.Maximum, Me.SelectedIndex + Me.DrawCount)
                EnsureVisible(Me.SelectedIndex)
                Me.Refresh()
            Case Keys.PageUp
                Me.SelectedIndex = Math.Max(Me.vs.Minimum, Me.SelectedIndex - Me.DrawCount)
                EnsureVisible(Me.SelectedIndex)
                Me.Refresh()
            Case Keys.Home
                Me.SelectedIndex = 0
                EnsureVisible(Me.SelectedIndex)
                Me.Refresh()
            Case Keys.End
                Me.SelectedIndex = Me.itemsAList.Count - 1
                EnsureVisible(Me.SelectedIndex)
                Me.Refresh()
        End Select

        MyBase.OnKeyDown(e)
    End Sub

    ' Calculate how many items we can draw given the height of the control.
    Protected ReadOnly Property DrawCount() As Integer
        Get
            If Me.vs.Value + Me.vs.LargeChange > Me.vs.Maximum Then
                Return Me.vs.Maximum - Me.vs.Value + 1
            Else
                Return Me.vs.LargeChange
            End If
        End Get
    End Property

    Protected Overrides Sub OnResize(ByVal e As EventArgs)
        Dim viewableItemCount As Integer = Me.ClientSize.Height / Me.ItemHeight

        Me.vs.Bounds = New Rectangle(Me.ClientSize.Width - SCROLL_WIDTH, 0, SCROLL_WIDTH, Me.ClientSize.Height)


        ' Determine if scrollbars are needed
        If Me.itemsAList.Count > viewableItemCount Then
            Me.vs.Visible = True
            Me.vs.LargeChange = viewableItemCount
            Me.offScreenBitmap = New Bitmap(Me.ClientSize.Width - SCROLL_WIDTH - 1, Me.ClientSize.Height - 2)
        Else
            Me.vs.Visible = False
            Me.vs.LargeChange = Me.itemsAList.Count
            Me.offScreenBitmap = New Bitmap(Me.ClientSize.Width - 1, Me.ClientSize.Height - 2)
        End If

        Me.vs.Maximum = Me.itemsAList.Count - 1
    End Sub
End Class

// Base custom control for DrawFontList
class OwnerDrawnListBox : Control
{
    const int SCROLL_WIDTH = 20;
    int itemHeight         = -1;
    int selectedIndex      = -1;

    Bitmap offScreen;
    VScrollBar vs;
    ArrayList items;

    public OwnerDrawnListBox()
    {
        this.vs = new VScrollBar();
        this.vs.Parent      = this;
        this.vs.Visible     = false;
        this.vs.SmallChange = 1;
        this.vs.ValueChanged += new EventHandler(this.ScrollValueChanged);

        this.items = new ArrayList();
    }

    public ArrayList Items
    {
        get
        {
            return this.items;
        }
    }

    protected Bitmap OffScreen
    {
        get
        {
            return this.offScreen;
        }
    }

    protected VScrollBar VScrollBar
    {
        get
        {
            return this.vs;
        }
    }

    public event EventHandler SelectedIndexChanged;

    // Raise the SelectedIndexChanged event
    protected virtual void OnSelectedIndexChanged(EventArgs e)
    {
        if(this.SelectedIndexChanged != null)
            this.SelectedIndexChanged(this, e);
    }

    protected override void OnMouseDown(MouseEventArgs e)
    {
        this.SelectedIndex = this.vs.Value + (e.Y / this.ItemHeight);

        // Invalidate the control so we can draw the item as selected.
        this.Refresh();
    }

    // Get or set index of selected item.
    public int SelectedIndex
    {
        get
        {
            return this.selectedIndex;
        }

        set
        {
            this.selectedIndex = value;

            if (this.SelectedIndexChanged != null)
                this.SelectedIndexChanged(this, EventArgs.Empty);

        }
    }

    protected void ScrollValueChanged(object o, EventArgs e)
    {
        this.Refresh();
    }

    protected virtual int ItemHeight
    {
        get
        {
            return this.itemHeight;
        }

        set
        {
            this.itemHeight = value;
        }
    }

    // If the requested index is before the first visible index then set the
    // first item to be the requested index. If it is after the last visible
    // index, then set the last visible index to be the requested index.
    public void EnsureVisible(int index)
    {
        if(index < this.vs.Value)
        {
            this.vs.Value = index;
            this.Refresh();
        }
        else if(index >= this.vs.Value + this.DrawCount)
        {
            this.vs.Value = index - this.DrawCount + 1;
            this.Refresh();
        }
    }


    // Need to set focus to the control when it
    // is clicked so that keyboard events occur.
    protected override void OnClick(EventArgs e)
    {
        this.Focus();
        base.OnClick(e);
    }

    // Selected item moves when you use the keyboard up/down keys.
    protected override void OnKeyDown(KeyEventArgs e)
    {
        switch(e.KeyCode)
        {
            case Keys.Down:
                if(this.SelectedIndex < this.vs.Maximum)
                {
                    EnsureVisible(++this.SelectedIndex);
                    this.Refresh();
                }
                break;
            case Keys.Up:
                if(this.SelectedIndex > this.vs.Minimum)
                {
                    EnsureVisible(--this.SelectedIndex);
                    this.Refresh();
                }
                break;
            case Keys.PageDown:
                this.SelectedIndex = Math.Min(this.vs.Maximum, this.SelectedIndex + this.DrawCount);
                EnsureVisible(this.SelectedIndex);
                this.Refresh();
                break;
            case Keys.PageUp:
                this.SelectedIndex = Math.Max(this.vs.Minimum, this.SelectedIndex - this.DrawCount);
                EnsureVisible(this.SelectedIndex);
                this.Refresh();
                break;
            case Keys.Home:
                this.SelectedIndex = 0;
                EnsureVisible(this.SelectedIndex);
                this.Refresh();
                break;
            case Keys.End:
                this.SelectedIndex = this.items.Count - 1;
                EnsureVisible(this.SelectedIndex);
                this.Refresh();
                break;
        }

        base.OnKeyDown(e);
    }

    // Calculate how many items we can draw given the height of the control.
    protected int DrawCount
    {
        get
        {
            if(this.vs.Value + this.vs.LargeChange > this.vs.Maximum)
                return this.vs.Maximum - this.vs.Value + 1;
            else
                return this.vs.LargeChange;
        }
    }

    protected override void OnResize(EventArgs e)
    {
        int viewableItemCount = this.ClientSize.Height / this.ItemHeight;

        this.vs.Bounds = new Rectangle(this.ClientSize.Width - SCROLL_WIDTH,
            0,
            SCROLL_WIDTH,
            this.ClientSize.Height);


        // Determine if scrollbars are needed
        if(this.items.Count > viewableItemCount)
        {
            this.vs.Visible = true;
            this.vs.LargeChange = viewableItemCount;
            this.offScreen = new Bitmap(this.ClientSize.Width - SCROLL_WIDTH - 1, this.ClientSize.Height - 2);
        }
        else
        {
            this.vs.Visible = false;
            this.vs.LargeChange = this.items.Count;
            this.offScreen = new Bitmap(this.ClientSize.Width - 1, this.ClientSize.Height - 2);
        }

        this.vs.Maximum = this.items.Count - 1;
    }
}

Agregue la clase FontListBox (que es una implementación de OwnerDrawnListBox) al proyecto.

' Derive an implementation of the
' OwnerDrawnListBox class
Class FontListBox
    Inherits OwnerDrawnListBox
    Private Const FONT_SIZE As Integer = 10
    Private Const DRAW_OFFSET As Integer = 5


    Public Sub New()

        ' Determine what the item height should be
        ' by adding 30% padding after measuring
        ' the letter A with the selected font.
        Dim g As Graphics = Me.CreateGraphics()
        Me.ItemHeight = Fix(g.MeasureString("A", Me.Font).Height * 1.3)
        g.Dispose()
    End Sub

    ' Return the name of the selected font.
    Public ReadOnly Property SelectedFaceName() As String
        Get
            Return CStr(Me.Items(Me.SelectedIndex))
        End Get
    End Property


    ' Determine what the text color should be
    ' for the selected item drawn as highlighted
    Function CalcTextColor(ByVal backgroundColor As Color) As Color
        If backgroundColor.Equals(Color.Empty) Then
            Return Color.Black
        End If
        Dim sum As Integer = backgroundColor.R + backgroundColor.G + backgroundColor.B

        If sum > 256 Then
            Return Color.Black
        Else
            Return Color.White
        End If
    End Function

    Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
        Dim font As Font
        Dim fontColor As Color

        ' The base class contains a bitmap, offScreen, for constructing
        ' the control and is rendered when all items are populated.
        ' This technique prevents flicker.
        Dim gOffScreen As Graphics = Graphics.FromImage(Me.OffScreen)
        gOffScreen.FillRectangle(New SolidBrush(Me.BackColor), Me.ClientRectangle)

        Dim itemTop As Integer = 0

        ' Draw the fonts in the list.
        Dim n As Integer
        For n = Me.VScrollBar.Value To (Me.VScrollBar.Value + DrawCount) - 1
            ' If the font name contains "dings" it needs to be displayed
            ' in the list box with a readable font with the default font.
            If CStr(Me.Items(n)).ToLower().IndexOf("dings") <> -1 Then
                font = New Font(Me.Font.Name, FONT_SIZE, FontStyle.Regular)
            Else
                font = New Font(CStr(Me.Items(n)), FONT_SIZE, FontStyle.Regular)
            End If
            ' Draw the selected item to appear highlighted
            If n = Me.SelectedIndex Then
                gOffScreen.FillRectangle(New SolidBrush(SystemColors.Highlight), 1, itemTop + 1, Me.ClientSize.Width - IIf(Me.VScrollBar.Visible, Me.VScrollBar.Width, 2), Me.ItemHeight)
                ' If the scroll bar is visible, subtract the scrollbar width
                ' otherwise subtract 2 for the width of the rectangle
                fontColor = CalcTextColor(SystemColors.Highlight)
            Else
                fontColor = Me.ForeColor
            End If
            ' Draw the item
            gOffScreen.DrawString(CStr(Me.Items(n)), font, New SolidBrush(fontColor), DRAW_OFFSET, itemTop)
            itemTop += Me.ItemHeight
        Next n

        ' Draw the list box
        e.Graphics.DrawImage(Me.OffScreen, 1, 1)

        gOffScreen.Dispose()
    End Sub


    ' Draws the external border around the control.
    Protected Overrides Sub OnPaintBackground(ByVal e As PaintEventArgs)
        e.Graphics.DrawRectangle(New Pen(Color.Black), 0, 0, Me.ClientSize.Width - 1, Me.ClientSize.Height - 1)
    End Sub
End Class

// Derive an implementation of the
// OwnerDrawnListBox class
class FontListBox : OwnerDrawnListBox
{
    const int FONT_SIZE    = 10;
    const int DRAW_OFFSET  = 5;

    public FontListBox()
    {

        // Determine what the item height should be
        // by adding 30% padding after measuring
        // the letter A with the selected font.
        Graphics g = this.CreateGraphics();
        this.ItemHeight = (int)(g.MeasureString("A", this.Font).Height * 1.3);
        g.Dispose();
    }

    // Return the name of the selected font.
    public string SelectedFaceName
    {
        get
        {
            return (string)this.Items[this.SelectedIndex];
        }
    }

    // Determine what the text color should be
    // for the selected item drawn as highlighted
    Color CalcTextColor(Color backgroundColor)
    {
        if(backgroundColor.Equals(Color.Empty))
            return Color.Black;

        int sum = backgroundColor.R + backgroundColor.G + backgroundColor.B;

        if(sum > 256)
            return Color.Black;
        else
            return Color.White;
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        Font font;
        Color fontColor;

        // The base class contains a bitmap, offScreen, for constructing
        // the control and is rendered when all items are populated.
        // This technique prevents flicker.
        Graphics gOffScreen = Graphics.FromImage(this.OffScreen);
        gOffScreen.FillRectangle(new SolidBrush(this.BackColor), this.ClientRectangle);

        int itemTop = 0;

        // Draw the fonts in the list.
        for(int n = this.VScrollBar.Value; n < this.VScrollBar.Value + DrawCount; n++)
        {
            // If the font name contains "dings" it needs to be displayed
            // in the list box with a readable font with the default font.
            if(((string)this.Items[n]).ToLower().IndexOf("dings") != -1)
                font = new Font(this.Font.Name, FONT_SIZE, FontStyle.Regular);
            else
                font = new Font((string)this.Items[n], FONT_SIZE, FontStyle.Regular);

            // Draw the selected item to appear highlighted
            if(n == this.SelectedIndex)
            {
                gOffScreen.FillRectangle(new SolidBrush(SystemColors.Highlight),
                    1,
                    itemTop + 1,
                    // If the scroll bar is visible, subtract the scrollbar width
                    // otherwise subtract 2 for the width of the rectangle
                    this.ClientSize.Width - (this.VScrollBar.Visible ? this.VScrollBar.Width : 2),
                    this.ItemHeight);
                fontColor = CalcTextColor(SystemColors.Highlight);
            }
            else
                fontColor = this.ForeColor;

            // Draw the item
            gOffScreen.DrawString((string)this.Items[n], font, new SolidBrush(fontColor), DRAW_OFFSET, itemTop);
            itemTop += this.ItemHeight;
        }

        // Draw the list box
        e.Graphics.DrawImage(this.OffScreen, 1, 1);

        gOffScreen.Dispose();
    }

    // Draws the external border around the control.

    protected override void OnPaintBackground(PaintEventArgs e)
    {
        e.Graphics.DrawRectangle(new Pen(Color.Black), 0, 0, this.ClientSize.Width - 1, this.ClientSize.Height - 1);
    }
}

En el formulario, agregue dos controles Label y asígneles los nombres descLabel y sampleLabel; el segundo mostrará un ejemplo de fuente seleccionado de FontListBox.
Cree una instancia de FontListBox para el formulario.

Agregue el código siguiente al constructor del evento Load para el formulario.

' Create a new instance of FontListBox.
myListBox.Parent = Me

' Configure the event handler for the SelectedIndexChanged event. 
AddHandler myListBox.SelectedIndexChanged, AddressOf Me.SelectedIndexChanged

' Draw the bounds of the FontListBox.
myListBox.Bounds = New Rectangle(5, 5, 150, 100)

' Add fonts to list, repeat the list 4 times
' so that the scroll bar can be demonstrated.
Dim n As Integer
For n = 0 To 3
    myListBox.Items.Add("Bookdings")
    myListBox.Items.Add("Courier New")
    myListBox.Items.Add("Frutiger Linotype")
    myListBox.Items.Add("Tahoma")
Next n


' Labels to show the selected font from the list box. Assumes
' instances of these labels have been declared for the form.
descLabel.Parent = Me
descLabel.Text = "Font Sample:"
descLabel.Bounds = New Rectangle(10, myListBox.Bottom + 20, Me.ClientSize.Width - 10, 30)

' Assumes an instance sampleLabel is declared for the form.
sampleLabel.Parent = Me
sampleLabel.Bounds = New Rectangle(10, descLabel.Bottom, Me.ClientSize.Width - 10, 30)
sampleLabel.Text = "AaBbCc 123"

// Create a new instance of FontListBox.
box = new FontListBox();
box.Parent = this;

// Configure the event handler for the SelectedIndexChanged event.
box.SelectedIndexChanged += new EventHandler(this.SelectedIndexChanged);

// Draw the bounds of the FontListBox.
box.Bounds = new Rectangle(5, 5, 150, 100);

// Add fonts to list, repeat the list 4 times
// so that the scroll bar can be demonstrated.
for(int n = 0; n < 4; n++)
{
    box.Items.Add("Bookdings");
    box.Items.Add("Courier New");
    box.Items.Add("Frutiger Linotype");
    box.Items.Add("Tahoma");
}


// Labels to show the selected font and a sample.
Label desc = new Label();
desc.Parent = this;
desc.Text = "Font Sample:";
desc.Bounds = new Rectangle(10, box.Bottom + 20, this.ClientSize.Width - 10, 30);

sample = new Label();
sample.Parent = this;
sample.Bounds = new Rectangle(10, desc.Bottom, this.ClientSize.Width - 10, 30);
sample.Text = "AaBbCc 123";

Agregue código para el evento SelectedChangedEvent del control FontListBox, con lo que se muestra la fuente seleccionada en el control sampleLabel.

' Event handler for SelectedIndexChanged to
' display a sample of the selected font.

' Assumes that an instace of myListBox has been declared for the form.
Friend Sub SelectedIndexChanged(ByVal o As Object, ByVal e As EventArgs)
    sampleLabel.Font = New Font(myListBox.SelectedFaceName, 12, FontStyle.Regular)
End Sub

// Event handler for SelectedIndexChanged to
// display a sample of the selected font.
private void SelectedIndexChanged(object o, EventArgs e)
{
    sample.Font = new Font(box.SelectedFaceName, 12, FontStyle.Regular);
}

Compilar el código

Para este ejemplo se requieren referencias a los siguientes espacios de nombres:

Vea también

Conceptos

Desarrollo de controles personalizados

.Temas "Cómo..." de .NET Compact Framework

Compartir a través de

Cómo: Crear un cuadro de lista dibujado por el propietario

Para crear un cuadro de lista dibujado por el propietario

Compilar el código

Vea también

Conceptos

Recursos adicionales