WPF ComboBox SelectionChanged 和 DropDownClosed 事件不起作用

Question

我试图通过将方法链接到 WPF 中组合框的选择更改事件和 DropDownClosed 事件来调用方法，但是当我更改组合框中的项目时，它没有调用它应该调用的函数（在我的例子中是 OnMyComboBoxChanged1 和OnMyComboBoxChanged2）。

MainWindow.xaml.cs

 public partial class MainWindow : Window
    {
        public List<string > NameOfPerson { get; set; }
        public string SelectedComboBoxItem { get; set; }

        public MainWindow()
        {
            InitializeComponent();
            NameOfPerson = new List<string>();
            NameOfPerson.Add("Ram");
            NameOfPerson.Add("Sita");
            NameOfPerson.Add("Hari");
            NameOfPerson.Add("Kumar");
            NameOfPerson.Add("Jay");
            NameOfPerson.Add("Bikash");
            MyComboBox.ItemsSource = NameOfPerson;
           this.MyComboBox.SelectionChanged += new SelectionChangedEventHandler(OnMyComboBoxChanged1);
           this.MyComboBox.DropDownClosed += new System.EventHandler(OnMyComboBoxChanged2);
        }

        private void OnMyComboBoxChanged1(object sender, SelectionChangedEventArgs e)
        {
            SelectedComboBoxItem = this.MyComboBox.Text;
        }
        private void OnMyComboBoxChanged2(object sender, System.EventArgs e)
        {
            SelectedComboBoxItem = this.MyComboBox.Text;
        }

    }

XAML

 <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
        <StackPanel Orientation="Horizontal">
            <Label Content="Combobox"/>
            <ComboBox x:Name="MyComboBox" Margin="50,0,0,0" Width="80"/>
        </StackPanel>
        <StackPanel Orientation="Horizontal" Margin="0,10,0,0">
            <Label Content="The selected item is : "/>
            <Label Content="{Binding SelectedComboBoxItem}"/> 
        </StackPanel>
       
    </StackPanel>

感谢您的帮助

Answer 1

我试过了，调用了方法。问题可能是您使用了错误的属性来检索所选项目。试试这个：

SelectedComboBoxItem = this.MyComboBox.SelectedItem as string;

Answer 2

标签的内容不会更新，因为没有任何内容告诉它要更新 - 标准 C# 属性没有自动通知。

您需要实施 INotifyPropertyChanged for your SelectedComboBoxItem property, or even better switch to the MVVM 设计模式。

替代方法是使用直接数据绑定

<Label Content="{Binding ElementName="MyComboBox", Path=SelectedItem}" />

这是可行的，因为控件的属性（通常）DependencyProperties确实提供了更改通知。

评论后编辑

请post一个minimal, complete, and verifiable example然后...下面的代码对我来说工作正常。

public MainWindow()
{
    InitializeComponent();

    var NameOfPerson = new List<string>();
    NameOfPerson.Add("Ram");
    NameOfPerson.Add("Sita");
    NameOfPerson.Add("Hari");
    NameOfPerson.Add("Kumar");
    NameOfPerson.Add("Jay");
    NameOfPerson.Add("Bikash");
    MyComboBox.ItemsSource = NameOfPerson;

    MyComboBox.SelectionChanged += (s,e) => MyComboBoxOnSelectionChanged();
}

private void MyComboBoxOnSelectionChanged()
{
    SelectedComboBoxItem = MyComboBox.SelectedItem.ToString();
    Debugger.Break(); // proof that the event handler is being called
}

Answer 3

你需要做两件事。

您应该为您的属性 SelectedComboBoxItem 实现 INotifyPropertyChanged 带有支持字段的接口。
您需要像这样将 DataContext 设置为您的 class。

this.DataContext=这个；

Answer 4

下面是答案和工作代码，以备不时之需

MainWindow.xaml.cs

using System.ComponentModel;
using System.Windows;
using System.Collections.Generic;
using System.Windows.Controls;
using System.Diagnostics;

namespace Combobox
{
    public partial class MainWindow : Window, INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        public List<string> NameOfPerson { get; set; }
        private string _SelectedComboBoxItem;
        public string SelectedComboBoxItem
        {
            get
            {
                return _SelectedComboBoxItem;
            }

            set
            {
                if (_SelectedComboBoxItem == value)
                    return;
                _SelectedComboBoxItem = value;
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(SelectedComboBoxItem)));
            }
        }

        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = this;
            NameOfPerson = new List<string>();
            NameOfPerson.Add("Ram");
            NameOfPerson.Add("Sita");
            NameOfPerson.Add("Hari");
            NameOfPerson.Add("Kumar");
            NameOfPerson.Add("Jay");
            NameOfPerson.Add("Bikash");
            MyComboBox.ItemsSource = NameOfPerson;
            this.MyComboBox.SelectionChanged += OnMyComboBoxChanged1;
            this.MyComboBox.DropDownClosed += OnMyComboBoxChanged2;
        }


        private void OnMyComboBoxChanged1(object sender, SelectionChangedEventArgs e)
        {
            SelectedComboBoxItem = this.MyComboBox.SelectedItem as string;
        }
        private void OnMyComboBoxChanged2(object sender, System.EventArgs e)
        {
            SelectedComboBoxItem = this.MyComboBox.Text;
            Debugger.Break();
        }

    }

}

XAML

<Window x:Class="Combobox.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Combobox"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="300">
    <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
        <StackPanel Orientation="Horizontal">
            <Label Content="Combobox"/>
            <ComboBox x:Name="MyComboBox" Margin="50,0,0,0" Width="80"/>
        </StackPanel>
        <StackPanel Orientation="Horizontal" Margin="0,10,0,0">
            <Label Content="The selected item is : "/>
            <Label Content="{Binding SelectedComboBoxItem}"  />
        </StackPanel>
       
    </StackPanel>
</Window>

WPF ComboBox SelectionChanged 和 DropDownClosed 事件不起作用

WPF ComboBox SelectionChanged and DropDownClosed events is not working

wpf

events

combobox

selectionchanged