允许空值的下拉框

女爷i 2022-04-22 03:48 160阅读 0赞

LSComboBoxItem.cs

using System;
    using System.Net;
    using System.Windows;
    using System.Windows.Controls;
    using System.Windows.Documents;
    using System.Windows.Ink;
    using System.Windows.Input;
    using System.Windows.Media;
    using System.Windows.Media.Animation;
    using System.Windows.Shapes;
    
    namespace Longshine.SLLib.InputControls.LSComboBox.LSNullableComboBox
    {
        public class LSComboBoxItem
        {
            /// <summary>
            /// 显示字段 (DisplayMemberPath)
            /// </summary>
            public string DisplayString { get; set; }
    
            /// <summary>
            /// 选中项 (SelectedValuePath)
            /// </summary>
            public object ItemValue { get; set; }
        }
    }

LSComboBoxItemList.cs

using System.Collections.Generic;
    
    namespace Longshine.SLLib.InputControls.LSComboBox.LSNullableComboBox
    {
        public class ComboBoxItemList<T> : List<LSComboBoxItem>
        {
            public delegate string GetDisplayString(T t);
    
            public ComboBoxItemList(bool addEmptyItem, IEnumerable<T> items, GetDisplayString getDisplayString)
            {
                if (addEmptyItem)
                {
                    Add(new LSComboBoxItem { DisplayString = "------", ItemValue = null });
                }
    
                if (items != null)
                {
                    foreach (T item in items)
                    {
                        Add(new LSComboBoxItem { DisplayString = getDisplayString(item), ItemValue = item });
                    }
                }
            }
        }
    }

LSEnhancedComboBox.cs

using System.Windows;
    using System.Windows.Controls;
    
    namespace Longshine.SLLib.InputControls
    {
        /// <summary>
        /// 有默认空值的下拉框
        /// </summary>
        public class LSEnhancedComboBox : ComboBox
        {
            public static readonly DependencyProperty SelectedValuePathProperty = DependencyProperty.Register("SelectedValuePath", typeof(string), typeof(LSEnhancedComboBox), new PropertyMetadata(new PropertyChangedCallback(SelectedValuePathPropertyChanged)));
    
            public static readonly DependencyProperty SelectedValueProperty = DependencyProperty.Register("SelectedValue", typeof(object), typeof(LSEnhancedComboBox), new PropertyMetadata(new PropertyChangedCallback(SelectedValuePropertyChanged)));
    
            public LSEnhancedComboBox()
                : base()
            {
                this.DisplayMemberPath = "DisplayString";
                this.SelectedValuePath = "ItemValue";
                base.SelectionChanged += new SelectionChangedEventHandler(ComboBoxClassic_SelectionChanged);
            }
    
            protected void ComboBoxClassic_SelectionChanged(object sender, SelectionChangedEventArgs e)
            {
                if (SelectedItem != null && !string.IsNullOrEmpty(SelectedValuePath))
                {
                    SetValue(LSEnhancedComboBox.SelectedValueProperty, SelectedItem.GetType().GetProperty(SelectedValuePath).GetValue(SelectedItem, null));
                }
            }
    
            static void SelectedValuePathPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
            {
            }
    
            static void SelectedValuePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
            {
                LSEnhancedComboBox cmb = (LSEnhancedComboBox)d;
    
                foreach (var item in cmb.Items)
                {
                    var currentValue = item.GetType().GetProperty(cmb.SelectedValuePath).GetValue(item, null);
                    if (currentValue == null && e.NewValue == null)
                    {
                        cmb.SelectedItem = item;
                        return;
                    }
                    if (currentValue != null)
                    {
                        if (currentValue.Equals(e.NewValue))
                        {
                            cmb.SelectedItem = item;
                            return;
                        }
                    }
                }
                cmb.SelectedIndex = -1;
            }
    
            public string SelectedValuePath
            {
                get { return (string)GetValue(LSEnhancedComboBox.SelectedValuePathProperty); }
                set { SetValue(LSEnhancedComboBox.SelectedValuePathProperty, value); }
            }
    
            public object SelectedValue
            {
                get { return GetValue(SelectedValueProperty); }
                set { SetValue(LSEnhancedComboBox.SelectedValueProperty, value); }
            }
    
        }
    }

使用：

<inputcontrols:LSEnhancedComboBox x:Name="cbRYType" Grid.Column="1" Grid.Row="1"/>

void cbRYType_Loaded(object sender, RoutedEventArgs e)
            {
                var ws = WcfServiceClientFactory<ComServiceClient, ComService>.CreateServiceClient();
                ws.GetCodeTableDataCompleted += (ss, e2) =>
                    {
                        if (e2.Error != null)
                            System.Windows.Browser.HtmlPage.Window.Alert(e2.Error.Message);
                        else
                        {
                            if (e2.Result == null) return;
    
                            ComboBoxItemList<CodeEntity> dataList = new ComboBoxItemList<CodeEntity>(true,
                                                                         e2.Result,
                                                                         c => c.MC0000);
                            this.cbRYType.ItemsSource = dataList;
                            this.cbRYType.SelectedIndex = 0;
                        }
    
                    };
                ws.GetCodeTableDataAsync("BM_KK");
            }

界面：

![1c110fa9-6773-38ef-a7d4-b405f78e5cfc.png][]

[1c110fa9-6773-38ef-a7d4-b405f78e5cfc.png]: /images/20220422/cecf9d0479ee4d5998cf3c6dff69be46.png