我有一个简单的表单,它使用 DataBinding 绑定到对象集合。最初我不希望 ComboBox 显示选择,所以我将其选定的索引设置为 -1。但是,当 ComboBox 被选中时,我无法在不选择值的情况下取消选择它。
如何在不选择值的情况下取消选择 ComboBox(选择其他控件)?
要重新创建,请创建一个新的 winform,添加一个 ComboBox 和一个 TextBox,然后使用以下代码:
Imports System.Collections.Generic
Public Class Form1
Public Property f As Person
Public Sub New()
' This call is required by the designer.
InitializeComponent()
' Add any initialization after the InitializeComponent() call.
Dim db As New People
' ComboBox1.CausesValidation = False
ComboBox1.DataSource = db
ComboBox1.DisplayMember = "Name"
ComboBox1.DataBindings.Add("SelectedItem", Me, "f", False, DataSourceUpdateMode.OnPropertyChanged)
ComboBox1.SelectedIndex = -1
End Sub
End Class
Public Class Person
Public Property Name As String
End Class
Public Class People
Inherits List(Of Person)
Public Sub New()
Me.Add(New Person With {.Name = "Dave"})
Me.Add(New Person With {.Name = "Bob"})
Me.Add(New Person With {.Name = "Steve"})
End Sub
End Class
当窗体启动时,应该选择 ComboBox,而不能选择 TextBox。
我发现将 ComboBox 上的 CausesValidation 切换为 False 可以解决问题,但会破坏数据绑定。
找到了解决办法!(谢谢伊万!)
如果 ComboBox 在验证时作为 SelectedIndex 为 -1,则暂时禁用绑定。
AddHandler ComboBox1.Validating, AddressOf DisableBindingWhenNothingSelected
AddHandler ComboBox1.Validated, AddressOf DisableBindingWhenNothingSelected
''' <summary>
''' Temporarily disables binding when nothing is selected.
''' </summary>
''' <param name="sender">Sender of the event.</param>
''' <param name="e">Event arguments.</param>
''' <remarks>A list bound ComboBox (and more generically ListControl) cannot be deselected,
''' because CurrencyManager does not allow setting the Position to -1 when the underlying list Count is > 0.
''' This should be bound to the Validating and Validated events of all ComboBoxes that have an initial SelectedIndex of -1.</remarks>
Protected Sub DisableBindingWhenNothingSelected(sender As Object, e As EventArgs)
Dim cb As ComboBox = DirectCast(sender, ComboBox)
If cb.SelectedIndex = -1 Then
If (cb.DataBindings.Count = 0) Then Exit Sub
If cb.DataBindings(0).DataSourceUpdateMode = DataSourceUpdateMode.Never Then
cb.DataBindings(0).DataSourceUpdateMode = DataSourceUpdateMode.OnPropertyChanged
Else
cb.DataBindings(0).DataSourceUpdateMode = DataSourceUpdateMode.Never
End If
End If
End Sub
本文收集自互联网,转载请注明来源。
如有侵权,请联系 [email protected] 删除。
我来说两句