TreeView.ShowPlusMinus 属性
获取或设置一个值，用以指示是否在包含子树节点的树节点旁显示加号 (+) 和减号 (-) 按钮。
**命名空间:**System.Windows.Forms
**程序集:**System.Windows.Forms（在 system.windows.forms.dll 中）
语法
声明
Public Property ShowPlusMinus As Boolean
用法
Dim instance As TreeView
Dim value As Boolean
value = instance.ShowPlusMinus
instance.ShowPlusMinus = value
public bool ShowPlusMinus { get; set; }
public:
property bool ShowPlusMinus {
bool get ();
void set (bool value);
}
/** @property */
public boolean get_ShowPlusMinus ()
/** @property */
public void set_ShowPlusMinus (boolean value)
public function get ShowPlusMinus () : boolean
public function set ShowPlusMinus (value : boolean)
属性值
如果在包含子树节点的树节点旁显示加号和减号按钮，则为 true；否则为 false。默认为 true。
备注
只有当 ShowRootLines 属性值为 true 时，才会在根树节点旁显示加号和减号按钮。如果未显示加号和减号按钮，则没有视觉提示来指示树节点包含子树节点且可以展开。此时，用户必须双击树节点，才能确定它是否包含子树节点，或者将其展开或折叠。
示例
下面的代码示例演示一个自定义的 TreeView。通过继承 TreeView 类，此自定义版本具有典型 TreeView 的所有功能。在构造函数中更改不同的属性值可以提供独特的外观。由于 ShowPlusMinus 属性设置为 false，因此该自定义控件还重写 OnAfterSelect 方法，以便单击节点时能够展开和折叠它们。
以这种方式自定义的控件可以在整个单位中使用，因此很容易提供一致的界面，而不需要在每个单独的项目中指定控件属性。
Public Class CustomizedTreeView
Inherits TreeView
Public Sub New()
' Customize the TreeView control by setting various properties.
BackColor = System.Drawing.Color.CadetBlue
FullRowSelect = True
HotTracking = True
Indent = 34
ShowPlusMinus = False
' The ShowLines property must be false for the FullRowSelect
' property to work.
ShowLines = False
End Sub 'New
Protected Overrides Sub OnAfterSelect(ByVal e As TreeViewEventArgs)
' Confirm that the user initiated the selection.
' This prevents the first node from expanding when it is
' automatically selected during the initialization of
' the TreeView control.
If e.Action <> TreeViewAction.Unknown Then
If e.Node.IsExpanded Then
e.Node.Collapse()
Else
e.Node.Expand()
End If
End If
' Remove the selection. This allows the same node to be
' clicked twice in succession to toggle the expansion state.
SelectedNode = Nothing
End Sub 'OnAfterSelect
End Class 'CustomizedTreeView
public class CustomizedTreeView : TreeView
{
public CustomizedTreeView()
{
// Customize the TreeView control by setting various properties.
BackColor = System.Drawing.Color.CadetBlue;
FullRowSelect = true;
HotTracking = true;
Indent = 34;
ShowPlusMinus = false;
// The ShowLines property must be false for the FullRowSelect
// property to work.
ShowLines = false;
}
protected override void OnAfterSelect(TreeViewEventArgs e)
{
// Confirm that the user initiated the selection.
// This prevents the first node from expanding when it is
// automatically selected during the initialization of
// the TreeView control.
if (e.Action != TreeViewAction.Unknown)
{
if (e.Node.IsExpanded)
{
e.Node.Collapse();
}
else
{
e.Node.Expand();
}
}
// Remove the selection. This allows the same node to be
// clicked twice in succession to toggle the expansion state.
SelectedNode = null;
}
}
public ref class CustomizedTreeView: public TreeView
{
public:
CustomizedTreeView()
{
// Customize the TreeView control by setting various properties.
BackColor = System::Drawing::Color::CadetBlue;
FullRowSelect = true;
HotTracking = true;
Indent = 34;
ShowPlusMinus = false;
// The ShowLines property must be false for the FullRowSelect
// property to work.
ShowLines = false;
}
protected:
virtual void OnAfterSelect( TreeViewEventArgs^ e ) override
{
// Confirm that the user initiated the selection.
// This prevents the first node from expanding when it is
// automatically selected during the initialization of
// the TreeView control.
if ( e->Action != TreeViewAction::Unknown )
{
if ( e->Node->IsExpanded )
{
e->Node->Collapse();
}
else
{
e->Node->Expand();
}
}
// Remove the selection. This allows the same node to be
// clicked twice in succession to toggle the expansion state.
SelectedNode = nullptr;
}
};
public class CustomizedTreeView extends TreeView
{
public CustomizedTreeView()
{
// Customize the TreeView control by setting various properties.
set_BackColor(System.Drawing.Color.get_CadetBlue());
set_FullRowSelect(true);
set_HotTracking(true);
set_Indent(34);
set_ShowPlusMinus(false);
// The ShowLines property must be false for the FullRowSelect
// property to work.
set_ShowLines(false);
} //CustomizedTreeView
protected void OnAfterSelect(TreeViewEventArgs e)
{
// Confirm that the user initiated the selection.
// This prevents the first node from expanding when it is
// automatically selected during the initialization of
// the TreeView control.
if (!(e.get_Action().Equals(TreeViewAction.Unknown))) {
if (e.get_Node().get_IsExpanded()) {
e.get_Node().Collapse();
}
else {
e.get_Node().Expand();
}
}
// Remove the selection. This allows the same node to be
// clicked twice in succession to toggle the expansion state.
set_SelectedNode(null);
} //OnAfterSelect
}//CustomizedTreeView
平台
Windows 98、Windows 2000 SP4、Windows CE、Windows Millennium Edition、Windows Mobile for Pocket PC、Windows Mobile for Smartphone、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition
.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。
版本信息
.NET Framework
受以下版本支持：2.0、1.1、1.0
.NET Compact Framework
受以下版本支持：2.0、1.0
请参见
参考
TreeView 类
TreeView 成员
System.Windows.Forms 命名空间
ShowRootLines