TreeView.DrawNode 事件
定义
重要
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在绘制 TreeView 并且将 DrawMode 属性设置为 TreeViewDrawMode 值而不是 Normal 时发生。
public:
event System::Windows::Forms::DrawTreeNodeEventHandler ^ DrawNode;public event System.Windows.Forms.DrawTreeNodeEventHandler DrawNode;public event System.Windows.Forms.DrawTreeNodeEventHandler? DrawNode;member this.DrawNode : System.Windows.Forms.DrawTreeNodeEventHandler Public Custom Event DrawNode As DrawTreeNodeEventHandler 事件类型
示例
下面的代码示例演示如何使用所有者绘图自定义 TreeView 控件。 TreeView示例中的 控件在标准节点标签旁边显示可选节点标记。 节点标记是使用 TreeNode.Tag 属性指定的。 控件 TreeView 还使用自定义颜色，其中包括自定义突出显示颜色。
可以通过设置颜色属性来自定义大多数 TreeView 颜色，但选择突出显示颜色不能作为属性使用。 此外，默认选择突出显示矩形仅围绕节点标签扩展。 必须使用所有者绘图来绘制节点标记，并绘制足够大以包含节点标记的自定义突出显示矩形。
在示例中，事件的处理程序 DrawNode 手动绘制节点标记和自定义选择突出显示。 未选择的节点不需要自定义。 对于这些， DrawTreeNodeEventArgs.DrawDefault 属性设置为 true ，以便由操作系统绘制它们。
此外，事件的 MouseDown 处理程序提供命中测试。 默认情况下，只能通过单击节点标签周围的区域来选择节点。 事件处理程序 MouseDown 选择在此区域中的任意位置或节点标记周围区域中单击的节点（如果存在）。
#using <System.dll>
#using <System.Windows.Forms.dll>
#using <System.Drawing.dll>
using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
public ref class TreeViewOwnerDraw: public Form
{
private:
TreeView^ myTreeView;
// Create a Font object for the node tags.
System::Drawing::Font^ tagFont;
public:
TreeViewOwnerDraw()
{
tagFont = gcnew System::Drawing::Font( "Helvetica",8,FontStyle::Bold );
// Create and initialize the TreeView control.
myTreeView = gcnew TreeView;
myTreeView->Dock = DockStyle::Fill;
myTreeView->BackColor = Color::Tan;
myTreeView->CheckBoxes = true;
// Add nodes to the TreeView control.
TreeNode^ node;
for ( int x = 1; x < 4; ++x )
{
// Add a root node to the TreeView control.
node = myTreeView->Nodes->Add( String::Format( "Task {0}", x ) );
for ( int y = 1; y < 4; ++y )
{
// Add a child node to the root node.
node->Nodes->Add( String::Format( "Subtask {0}", y ) );
}
}
myTreeView->ExpandAll();
// Add tags containing alert messages to a few nodes
// and set the node background color to highlight them.
myTreeView->Nodes[ 1 ]->Nodes[ 0 ]->Tag = "urgent!";
myTreeView->Nodes[ 1 ]->Nodes[ 0 ]->BackColor = Color::Yellow;
myTreeView->SelectedNode = myTreeView->Nodes[ 1 ]->Nodes[ 0 ];
myTreeView->Nodes[ 2 ]->Nodes[ 1 ]->Tag = "urgent!";
myTreeView->Nodes[ 2 ]->Nodes[ 1 ]->BackColor = Color::Yellow;
// Configure the TreeView control for owner-draw and add
// a handler for the DrawNode event.
myTreeView->DrawMode = TreeViewDrawMode::OwnerDrawText;
myTreeView->DrawNode += gcnew DrawTreeNodeEventHandler( this, &TreeViewOwnerDraw::myTreeView_DrawNode );
// Add a handler for the MouseDown event so that a node can be
// selected by clicking the tag text as well as the node text.
myTreeView->MouseDown += gcnew MouseEventHandler( this, &TreeViewOwnerDraw::myTreeView_MouseDown );
// Initialize the form and add the TreeView control to it.
this->ClientSize = System::Drawing::Size( 292, 273 );
this->Controls->Add( myTreeView );
}
protected:
// Clean up any resources being used.
~TreeViewOwnerDraw()
{
if ( tagFont != nullptr )
{
delete tagFont;
}
}
// Draws a node.
private:
void myTreeView_DrawNode( Object^ sender, DrawTreeNodeEventArgs^ e )
{
// Draw the background and node text for a selected node.
if ( (e->State & TreeNodeStates::Selected) != (TreeNodeStates)0 )
{
// Draw the background of the selected node. The NodeBounds
// method makes the highlight rectangle large enough to
// include the text of a node tag, if one is present.
e->Graphics->FillRectangle( Brushes::Green, NodeBounds( e->Node ) );
// Retrieve the node font. If the node font has not been set,
// use the TreeView font.
System::Drawing::Font^ nodeFont = e->Node->NodeFont;
if ( nodeFont == nullptr )
nodeFont = (dynamic_cast<TreeView^>(sender))->Font;
// Draw the node text.
e->Graphics->DrawString( e->Node->Text, nodeFont, Brushes::White, Rectangle::Inflate( e->Bounds, 2, 0 ) );
}
// Use the default background and node text.
else
{
e->DrawDefault = true;
}
// If a node tag is present, draw its string representation
// to the right of the label text.
if ( e->Node->Tag != nullptr )
{
e->Graphics->DrawString( e->Node->Tag->ToString(), tagFont, Brushes::Yellow, (float)e->Bounds.Right + 2, (float)e->Bounds.Top );
}
// If the node has focus, draw the focus rectangle large, making
// it large enough to include the text of the node tag, if present.
if ( (e->State & TreeNodeStates::Focused) != (TreeNodeStates)0 )
{
Pen^ focusPen = gcnew Pen( Color::Black );
try
{
focusPen->DashStyle = System::Drawing::Drawing2D::DashStyle::Dot;
Rectangle focusBounds = NodeBounds( e->Node );
focusBounds.Size = System::Drawing::Size( focusBounds.Width - 1, focusBounds.Height - 1 );
e->Graphics->DrawRectangle( focusPen, focusBounds );
}
finally
{
if ( focusPen )
delete safe_cast<IDisposable^>(focusPen);
}
}
}
// Selects a node that is clicked on its label or tag text.
void myTreeView_MouseDown( Object^ /*sender*/, MouseEventArgs^ e )
{
TreeNode^ clickedNode = myTreeView->GetNodeAt( e->X, e->Y );
if ( NodeBounds( clickedNode ).Contains( e->X, e->Y ) )
{
myTreeView->SelectedNode = clickedNode;
}
}
// Returns the bounds of the specified node, including the region
// occupied by the node label and any node tag displayed.
Rectangle NodeBounds( TreeNode^ node )
{
// Set the return value to the normal node bounds.
Rectangle bounds = node->Bounds;
if ( node->Tag != nullptr )
{
// Retrieve a Graphics object from the TreeView handle
// and use it to calculate the display width of the tag.
Graphics^ g = myTreeView->CreateGraphics();
int tagWidth = (int)g->MeasureString( node->Tag->ToString(), tagFont ).Width + 6;
// Adjust the node bounds using the calculated value.
bounds.Offset( tagWidth / 2, 0 );
bounds = Rectangle::Inflate( bounds, tagWidth / 2, 0 );
g->~Graphics();
}
return bounds;
}
};
[STAThreadAttribute]
int main()
{
Application::Run( gcnew TreeViewOwnerDraw );
}
using System;
using System.Drawing;
using System.Windows.Forms;
public class TreeViewOwnerDraw : Form
{
private TreeView myTreeView;
// Create a Font object for the node tags.
Font tagFont = new Font("Helvetica", 8, FontStyle.Bold);
public TreeViewOwnerDraw()
{
// Create and initialize the TreeView control.
myTreeView = new TreeView();
myTreeView.Dock = DockStyle.Fill;
myTreeView.BackColor = Color.Tan;
myTreeView.CheckBoxes = true;
// Add nodes to the TreeView control.
TreeNode node;
for (int x = 1; x < 4; ++x)
{
// Add a root node to the TreeView control.
node = myTreeView.Nodes.Add(String.Format("Task {0}", x));
for (int y = 1; y < 4; ++y)
{
// Add a child node to the root node.
node.Nodes.Add(String.Format("Subtask {0}", y));
}
}
myTreeView.ExpandAll();
// Add tags containing alert messages to a few nodes
// and set the node background color to highlight them.
myTreeView.Nodes[1].Nodes[0].Tag = "urgent!";
myTreeView.Nodes[1].Nodes[0].BackColor = Color.Yellow;
myTreeView.SelectedNode = myTreeView.Nodes[1].Nodes[0];
myTreeView.Nodes[2].Nodes[1].Tag = "urgent!";
myTreeView.Nodes[2].Nodes[1].BackColor = Color.Yellow;
// Configure the TreeView control for owner-draw and add
// a handler for the DrawNode event.
myTreeView.DrawMode = TreeViewDrawMode.OwnerDrawText;
myTreeView.DrawNode +=
new DrawTreeNodeEventHandler(myTreeView_DrawNode);
// Add a handler for the MouseDown event so that a node can be
// selected by clicking the tag text as well as the node text.
myTreeView.MouseDown += new MouseEventHandler(myTreeView_MouseDown);
// Initialize the form and add the TreeView control to it.
this.ClientSize = new Size(292, 273);
this.Controls.Add(myTreeView);
}
// Clean up any resources being used.
protected override void Dispose(bool disposing)
{
if (disposing)
{
tagFont.Dispose();
}
base.Dispose(disposing);
}
[STAThreadAttribute()]
static void Main()
{
Application.Run(new TreeViewOwnerDraw());
}
// Draws a node.
private void myTreeView_DrawNode(
object sender, DrawTreeNodeEventArgs e)
{
// Draw the background and node text for a selected node.
if ((e.State & TreeNodeStates.Selected) != 0)
{
// Draw the background of the selected node. The NodeBounds
// method makes the highlight rectangle large enough to
// include the text of a node tag, if one is present.
e.Graphics.FillRectangle(Brushes.Green, NodeBounds(e.Node));
// Retrieve the node font. If the node font has not been set,
// use the TreeView font.
Font nodeFont = e.Node.NodeFont;
if (nodeFont == null) nodeFont = ((TreeView)sender).Font;
// Draw the node text.
e.Graphics.DrawString(e.Node.Text, nodeFont, Brushes.White,
Rectangle.Inflate(e.Bounds, 2, 0));
}
// Use the default background and node text.
else
{
e.DrawDefault = true;
}
// If a node tag is present, draw its string representation
// to the right of the label text.
if (e.Node.Tag != null)
{
e.Graphics.DrawString(e.Node.Tag.ToString(), tagFont,
Brushes.Yellow, e.Bounds.Right + 2, e.Bounds.Top);
}
// If the node has focus, draw the focus rectangle large, making
// it large enough to include the text of the node tag, if present.
if ((e.State & TreeNodeStates.Focused) != 0)
{
using (Pen focusPen = new Pen(Color.Black))
{
focusPen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dot;
Rectangle focusBounds = NodeBounds(e.Node);
focusBounds.Size = new Size(focusBounds.Width - 1,
focusBounds.Height - 1);
e.Graphics.DrawRectangle(focusPen, focusBounds);
}
}
}
// Selects a node that is clicked on its label or tag text.
private void myTreeView_MouseDown(object sender, MouseEventArgs e)
{
TreeNode clickedNode = myTreeView.GetNodeAt(e.X, e.Y);
if (NodeBounds(clickedNode).Contains(e.X, e.Y))
{
myTreeView.SelectedNode = clickedNode;
}
}
// Returns the bounds of the specified node, including the region
// occupied by the node label and any node tag displayed.
private Rectangle NodeBounds(TreeNode node)
{
// Set the return value to the normal node bounds.
Rectangle bounds = node.Bounds;
if (node.Tag != null)
{
// Retrieve a Graphics object from the TreeView handle
// and use it to calculate the display width of the tag.
Graphics g = myTreeView.CreateGraphics();
int tagWidth = (int)g.MeasureString
(node.Tag.ToString(), tagFont).Width + 6;
// Adjust the node bounds using the calculated value.
bounds.Offset(tagWidth/2, 0);
bounds = Rectangle.Inflate(bounds, tagWidth/2, 0);
g.Dispose();
}
return bounds;
}
}
Imports System.Drawing
Imports System.Windows.Forms
Public Class TreeViewOwnerDraw
Inherits Form
Private WithEvents myTreeView As TreeView
' Create a Font object for the node tags.
Private tagFont As New Font("Helvetica", 8, FontStyle.Bold)
Public Sub New()
' Create and initialize the TreeView control.
myTreeView = New TreeView()
myTreeView.Dock = DockStyle.Fill
myTreeView.BackColor = Color.Tan
myTreeView.CheckBoxes = True
' Add nodes to the TreeView control.
Dim node As TreeNode
Dim x As Integer
For x = 1 To 3
' Add a root node to the TreeView control.
node = myTreeView.Nodes.Add(String.Format("Task {0}", x))
Dim y As Integer
For y = 1 To 3
' Add a child node to the root node.
node.Nodes.Add(String.Format("Subtask {0}", y))
Next y
Next x
myTreeView.ExpandAll()
' Add tags containing alert messages to a few nodes
' and set the node background color to highlight them.
myTreeView.Nodes(1).Nodes(0).Tag = "urgent!"
myTreeView.Nodes(1).Nodes(0).BackColor = Color.Yellow
myTreeView.SelectedNode = myTreeView.Nodes(1).Nodes(0)
myTreeView.Nodes(2).Nodes(1).Tag = "urgent!"
myTreeView.Nodes(2).Nodes(1).BackColor = Color.Yellow
' Configure the TreeView control for owner-draw.
myTreeView.DrawMode = TreeViewDrawMode.OwnerDrawText
' Add a handler for the MouseDown event so that a node can be
' selected by clicking the tag text as well as the node text.
AddHandler myTreeView.MouseDown, AddressOf myTreeView_MouseDown
' Initialize the form and add the TreeView control to it.
Me.ClientSize = New Size(292, 273)
Me.Controls.Add(myTreeView)
End Sub
<STAThreadAttribute()> _
Shared Sub Main()
Application.Run(New TreeViewOwnerDraw())
End Sub
' Draws a node.
Private Sub myTreeView_DrawNode(ByVal sender As Object, _
ByVal e As DrawTreeNodeEventArgs) Handles myTreeView.DrawNode
' Draw the background and node text for a selected node.
If (e.State And TreeNodeStates.Selected) <> 0 Then
' Draw the background of the selected node. The NodeBounds
' method makes the highlight rectangle large enough to
' include the text of a node tag, if one is present.
e.Graphics.FillRectangle(Brushes.Green, NodeBounds(e.Node))
' Retrieve the node font. If the node font has not been set,
' use the TreeView font.
Dim nodeFont As Font = e.Node.NodeFont
If nodeFont Is Nothing Then
nodeFont = CType(sender, TreeView).Font
End If
' Draw the node text.
e.Graphics.DrawString(e.Node.Text, nodeFont, Brushes.White, _
e.Bounds.Left - 2, e.Bounds.Top)
' Use the default background and node text.
Else
e.DrawDefault = True
End If
' If a node tag is present, draw its string representation
' to the right of the label text.
If (e.Node.Tag IsNot Nothing) Then
e.Graphics.DrawString(e.Node.Tag.ToString(), tagFont, _
Brushes.Yellow, e.Bounds.Right + 2, e.Bounds.Top)
End If
' If the node has focus, draw the focus rectangle large, making
' it large enough to include the text of the node tag, if present.
If (e.State And TreeNodeStates.Focused) <> 0 Then
Dim focusPen As New Pen(Color.Black)
Try
focusPen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dot
Dim focusBounds As Rectangle = NodeBounds(e.Node)
focusBounds.Size = New Size(focusBounds.Width - 1, _
focusBounds.Height - 1)
e.Graphics.DrawRectangle(focusPen, focusBounds)
Finally
focusPen.Dispose()
End Try
End If
End Sub
' Selects a node that is clicked on its label or tag text.
Private Sub myTreeView_MouseDown(ByVal sender As Object, ByVal e As MouseEventArgs)
Dim clickedNode As TreeNode = myTreeView.GetNodeAt(e.X, e.Y)
If NodeBounds(clickedNode).Contains(e.X, e.Y) Then
myTreeView.SelectedNode = clickedNode
End If
End Sub
' Returns the bounds of the specified node, including the region
' occupied by the node label and any node tag displayed.
Private Function NodeBounds(ByVal node As TreeNode) As Rectangle
' Set the return value to the normal node bounds.
Dim bounds As Rectangle = node.Bounds
If (node.Tag IsNot Nothing) Then
' Retrieve a Graphics object from the TreeView handle
' and use it to calculate the display width of the tag.
Dim g As Graphics = myTreeView.CreateGraphics()
Dim tagWidth As Integer = CInt(g.MeasureString( _
node.Tag.ToString(), tagFont).Width) + 6
' Adjust the node bounds using the calculated value.
bounds.Offset(tagWidth \ 2, 0)
bounds = Rectangle.Inflate(bounds, tagWidth \ 2, 0)
g.Dispose()
End If
Return bounds
End Function 'NodeBounds
End Class
注解
使用此事件可以使用所有者绘图自定义控件中 TreeView 节点的外观。
仅当 属性设置为 TreeViewDrawMode 或 OwnerDrawText的值OwnerDrawAll时DrawMode，才会引发此事件。 下表指示当 属性设置为这些值时DrawMode如何TreeNode自定义 。
| DrawMode 属性值 | TreeNode 自定义 |
|---|---|
| OwnerDrawText | TreeNode可以自定义标签区域。 系统会自动绘制所有其他 TreeNode 元素。 |
| OwnerDrawAll | 可以自定义整个 TreeNode 的外观。 如果需要，必须手动绘制图标、检查框、加号和减号以及连接节点的线条。 |
TreeNode.Text如果值是使用控件Font的 属性指定的TreeView字体绘制的，则该值将占用的区域是可以单击节点以选择它的区域。 这称为命中测试区域。 如果在此区域之外绘制，则应提供自己的代码，用于在单击节点的可见区域时选择节点。
使用 OwnerDrawText时，DrawTreeNodeEventArgs.Bounds命中测试区域对应于 属性。 但是，使用 OwnerDrawAll时， DrawTreeNodeEventArgs.Bounds 属性包含 的 TreeView整个宽度。 在这种情况下，可以通过获取 DrawTreeNodeEventArgs.Node 值并访问其 TreeNode.Bounds 属性来访问命中测试区域。 然后，可以在这些边界内绘制节点的命中测试区域，或者提供自己的命中测试代码。 请注意，设置 TreeNode.NodeFont 属性不会更改命中测试区域的大小，这是使用为整个 TreeView指定的字体计算的。
有关如何处理事件的详细信息，请参阅 处理和引发事件。
适用于
另请参阅
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