如何:创建一个所有者描述的列表框
更新:2007 年 11 月
您可以通过 .NET Compact Framework 创建所有者描述的列表框,但不像通过完整的 .NET Framework 创建那样容易。.NET Compact Framework 不支持 DrawMode、DrawItem 以及列表框和其他控件的其他描述成员,但可以通过编程实现该功能。此示例提供一个自定义控件类以创建所有者描述的列表框,并将该控件作为用于选择字体的列表框来实现。
此示例包含一个基类 OwnerDrawnListBox,FontListBox 派生自该基类。OwnerDrawnListBox 包括以下核心功能:
提供垂直滚动条、包含项的数组和用于构造列表框的位图。
提供项高度属性,并确定在给定控件高度的情况下可以描述多少项。
提供 SelectedIndex 属性,该属性通过当前滚动条、项高度以及鼠标指针的坐标值来确定所选项。
提供 SelectedIndexChanged 事件。
确保项的可见性。
在不需要时移除滚动条。
提供使用上/下导航键的键盘操作。
FontListBox 类从 OwnerDrawnListBox 继承。该类的实现和技术如下:
确定适当的项高度。
使用重写的 OnPaint 方法描述各项,并将选定的项描述为突出显示。为了防止闪烁,此方法将在描述完控件的所有图形特征后才显示控件。
提供 SelectedFaceName 属性,其中包含选定字体的名称。
DrawFontList 窗体执行的操作如下:
创建一个新的 FontListBox 实例,并将其添加到控件集合中。
为 SelectedIndexChanged 事件添加一个事件处理程序。
使用字体列表填充 FontListBox。
提供用于显示选定字体示例的标签。
创建所有者描述的列表框
将 OwnerDrawnListBox 自定义控件类添加到项目中。
' 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; } }
将 FontListBox 类(即 OwnerDrawnListBox 的实现)添加到项目中。
' 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); } }
在窗体中,添加两个 Label 控件,并将其分别命名为 descLabel 和 sampleLabel;后者将显示从 FontListBox 中选定的字体示例。
为窗体创建 FontListBox 的一个实例。
将以下代码添加到窗体的 Load 事件的构造函数中。
' 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";
在 FontListBox 控件的 SelectedChangedEvent 事件中添加代码,用于在 sampleLabel 控件中显示选定的字体。
' 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); }
编译代码
此示例需要引用下面的命名空间: