[英]Force a combobox to dropdown
昨天我遇到了一個帖子,我認為我得到了一個很好的解決方案。 這是鏈接http://www.blogs.intuidev.com/post/2011/01/02/combobox_autoopendropdown_attachedbehavior.aspx
我試圖關注該帖子,因為我是WPF和XAML的新手,我最后得到一個奇怪的錯誤: Type ComboBox_ForceDropDown initialization failed. The type initializer for ERP_Lite.Views.DesignRelatedCode.ComboBox_ForceDropDown threw an exception.
Type ComboBox_ForceDropDown initialization failed. The type initializer for ERP_Lite.Views.DesignRelatedCode.ComboBox_ForceDropDown threw an exception.
這是我的代碼:
//ComboBox_ForceDropDown.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
namespace ERP_Lite.Views.DesignRelatedCode
{
public static class ComboBox_ForceDropDown
{
public static readonly DependencyProperty OpenDropDownAutomaticallyProperty = DependencyProperty.Register
(
"OpenDropDownAutomatically",
typeof(bool),
typeof(ComboBox_ForceDropDown),
new UIPropertyMetadata(false, onOpenDropDownAutomatically_Changed)
);
public static bool GetOpenDropDownAutomatically(ComboBox cbo)
{
return (bool)cbo.GetValue(OpenDropDownAutomaticallyProperty);
}
public static void SetOpenDropDownAutomatically(ComboBox cbo, bool value)
{
cbo.SetValue(OpenDropDownAutomaticallyProperty, value);
}
/// <summary>
/// Fired when the assignment of the behavior changes (IOW, is being turned on or off).
/// </summary>
private static void onOpenDropDownAutomatically_Changed(DependencyObject doSource, DependencyPropertyChangedEventArgs e)
{
//The ComboBox that is the target of the assignment
ComboBox cbo = doSource as ComboBox;
if (cbo == null)
return;
//Just to be safe ...
if (e.NewValue is bool == false)
return;
if ((bool)e.NewValue)
{
//Attach
cbo.GotFocus += cbo_GotFocus;
cbo.LostFocus += cbo_LostFocus;
}
else
{
//Detach
cbo.GotFocus -= cbo_GotFocus;
cbo.LostFocus -= cbo_LostFocus;
}
}
private static void cbo_GotFocus(object sender, RoutedEventArgs e)
{
//Open the DropDown/popup as soon as the control is focused
((ComboBox)sender).IsDropDownOpen = true;
}
private static void cbo_LostFocus(object sender, RoutedEventArgs e)
{
((ComboBox)sender).IsDropDownOpen = false;
}
}
}
和xaml文件
//App.xaml
<Application
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:comboFDD="clr-namespace:ERP_Lite.Views.DesignRelatedCode"
x:Class="ERP_Lite.App" StartupUri="Views/MainWindow.xaml">
<Application.Resources>
<!-- Resources scoped at the Application level should be defined here. -->
<Style TargetType="{x:Type ComboBox}">
<Setter Property="StaysOpenOnEdit" Value="True" />
<Setter Property="comboFDD:ComboBox_ForceDropDown.OpenDropDownAutomatically" Value="True"/> <!--I get error on this line-->
</Style>
</Application.Resources>
</Application>
這是解決方案資源管理器的圖像:
更新 :內部異常詳細信息如下:
'ComboBox_ForceDropDown' type must derive from DependencyObject.
您的財產應該是Attached
DependancyProperty
。 更新您的屬性聲明,如:
public static readonly DependencyProperty OpenDropDownAutomaticallyProperty =
DependencyProperty.RegisterAttached("OpenDropDownAutomatically",
typeof(bool),
typeof(ComboBox_ForceDropDown),
new UIPropertyMetadata(false, onOpenDropDownAutomatically_Changed)
);
DependencyProperty
只能在派生自DependencyObject
類上定義。 您的類是靜態的,因此無法從DependencyObject
派生。 可能這是你例外的原因。
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