DataGrid 中的 WPF Combobox - SelectionChanged 事件将选定的 ComboBoxItem 返回为 null

Question

问题：在DataGrid的Combobox的SelectionChanged事件中，ComboboxItem始终为null。我可能遗漏了什么以及我们如何解决这个问题？请注意（如图 1 所示）如果您能够从组合框中 select 一个项目，这意味着组合框已经加载。因此它的 SelectionChanged 事件在组合框加载后被调用。

Employee.cs:

public class Employee
{
    public int EmployeeId { get; set; }
    public string Name { get; set; }
    public string StateName { get; set; }
}

State.cs:

public class State
{
    public string StateName { get; set; }
    public string StateCode { get; set; }
}

StateList.cs:

public class StateList : List<State>
{
    public StateList()
    {
        Add(new State { StateName = "Iowa", StateCode = "IA" });
        Add(new State { StateName = "Nebraska", StateCode = "NE" });
        Add(new State { StateName = "Ohio", StateCode = "OH" });
        Add(new State { StateName = "Virginia", StateCode = "VA" });
    }
}

Combobox SelectionChanged 事件 [always returns cmbItem as null]:

private void cmbState_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    StateList states = new StateList();
    string st = "";
    ComboBoxItem cmbItem = ((sender as ComboBox).SelectedItem as ComboBoxItem);
    if(cmbItem != null)
        st = "   You selected " + cmbItem.Content.ToString() + ".";
}

更改 selection 的快照：

ComboboxItem 显示为 null:

MainWindow.xaml:

<Window x:Class="WPF_DataGridCombobox.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        .......
        Title="MainWindow" Height="450" Width="800">

    <Window.Resources>
        <local:StateList x:Key="ListOfStates"/>
    </Window.Resources>
    <Grid>
        <DataGrid x:Name="dgEmplyees" AutoGenerateColumns="False">
            <DataGrid.Columns>
                <DataGridTemplateColumn Header="Update">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <Button x:Name="btnUpdate" Click="btnUpdate_Click"/>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
                <DataGridTextColumn Header="Name" Binding="{Binding  Name}"/>
                <DataGridTemplateColumn Header="State Name">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding StateName}"/>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                    <DataGridTemplateColumn.CellEditingTemplate>
                        <DataTemplate>
                            <ComboBox x:Name="cmbState" ItemsSource="{StaticResource ListOfStates}" DisplayMemberPath="StateName" SelectedValuePath="StateName" SelectedValue="{Binding StateName}" SelectionChanged="cmbState_SelectionChanged" IsEditable="False" IsReadOnly="True" />                            
                        </DataTemplate>
                    </DataGridTemplateColumn.CellEditingTemplate>
                </DataGridTemplateColumn>
            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>

Answer 1

我无法添加评论，所以我写在这里。在 microsoft 的示例中，他们将 ListBoxItem 类型的对象添加到列表框。所以这里SelectedItem可以解析为ListBoxItem。但是您使用列表 ListOfStates，因此 SelectedItem 的类型为 State。因此你必须写：State state = ((sender as ComboBox).SelectedItem as State);

Answer 2

((ComboBox)sender).SelectedItem as ComboBoxItem

是 null 因为 SelectedItem 不是 ComboBoxItem。如果您明确添加了 ComboBoxItems，它将是一个 ComboBoxItem，例如喜欢

<ComboBox>
    <ComboBoxItem>Item 1</ComboBoxItem>
    <ComboBoxItem>Item 2</ComboBoxItem>
<ComboBox>

由于您已将一组 State 对象分配给 ComboBox 的 ItemsSource 属性，因此 SelectedItem 是一个 State 对象：

private void cmbState_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    var state = (State)((ComboBox)sender).SelectedItem;
    ...
}

DataGrid 中的 WPF Combobox - SelectionChanged 事件将选定的 ComboBoxItem 返回为 null

WPF Combox in DataGrid - SelectionChanged event returning selected ComboBoxItem as null

c#

wpf

datagrid

combobox

datagridcomboboxcolumn