使用 DropDownOpened 刷新 ComboBox 导致丢失选中

Posted 2023-04-01

【中文标题】使用 DropDownOpened 刷新 ComboBox 导致丢失选中

【英文标题】：Refresh ComboBox with DropDownOpened result in loosing selected

【发布时间】：2021-09-18 18:25:48

【问题描述】：

我有一个包含活动网络接口条目的组合框。我喜欢在用户每次打开下拉菜单时刷新条目。

遗憾的是，如果 ComboBox 打开然后关闭（右侧有箭头），则不再显示所选条目。 ComboBox 显示为空。 My ComboBox before and after

如果我删除 DropDownOpened 事件，则在打开关闭 DropDown 后，所选项目将显示在 ComboBox 中。

感谢您的帮助。

这是我的看法：

                    <ComboBox ItemsSource="Binding HostInterfaces"
                              SelectedItem="Binding HostInterfaceSelected, Mode=TwoWay"
                              DisplayMemberPath="Indicator">
                        <i:Interaction.Triggers>
                            <i:EventTrigger EventName="DropDownOpened">
                                <i:InvokeCommandAction Command="Binding Path=DropDownOpenedCommand, Mode=OneWay" />
                            </i:EventTrigger>
                        </i:Interaction.Triggers>
                    </ComboBox>

这是我的视图模型：

    private RelayCommand _dropDownOpenedCommand;
    public ICommand DropDownOpenedCommand => _dropDownOpenedCommand ??
                                             (_dropDownOpenedCommand =
                                                 new RelayCommand(ExecuteDropDownOpenedCommand));

    private void ExecuteDropDownOpenedCommand(object obj)
    
        HostInterfaces.Clear();

        // add several entries
        _hostInterfaces.Add( ... );
    

    private readonly ObservableCollection<HostNetworkInterfaceEntry> _hostInterfaces = new ObservableCollection<HostNetworkInterfaceEntry>();
    public ObservableCollection<HostNetworkInterfaceEntry> HostInterfaces => _hostInterfaces;
    private HostNetworkInterfaceEntry _hostInterfaceSelected;
    public HostNetworkInterfaceEntry HostInterfaceSelected
    
        get => _hostInterfaceSelected;
        set
        
            if (value == null) return;
            if (value == _hostInterfaceSelected) return;
            _hostInterfaceSelected = value;
            OnPropertyChanged(nameof(HostInterfaceSelected));
        
    

我的 HostNetWorkInterfaceEntry 类：

public class HostNetworkInterfaceEntry

    public HostNetworkInterfaceEntry(string name, IPAddress address)
    
        Name = name;
        Address = address;
    

    public string Name  get; private set; 
    public IPAddress Address  get; private set; 
    public string Indicator => (Address != null ? $"Address   Name" : $"Name");

【问题讨论】：

value == _hostInterfaceSelected do reference equals ...明显的解决方案是提供自己的实现（覆盖object.Equals和相关）...也有可能SelectedItem在没有项目时无效...所以您需要在清除本地之前存储并在添加元素后恢复它

您正在清除HostInterfaces.Clear();，跟踪选择的值并在填充时再次选择正确的项目。

【参考方案1】：

感谢@Senir 和@Jeroen van Langen。您的提示引导我找到解决方案。

我必须修改属性 HostInterfaceSelected 以及 ExecuteDropDownOpenedCommand 方法。

public HostNetworkInterfaceEntry HostInterfaceSelected

    get => _hostInterfaceSelected;
    set
    
        // removed that -> if (value == null) return;
        if (value == _hostInterfaceSelected) return;
        _hostInterfaceSelected = value;
        OnPropertyChanged(nameof(HostInterfaceSelected));
    


private void ExecuteDropDownOpenedCommand(object obj)

    var saveSelected = HostInterfaceSelected; // added this
    HostInterfaces.Clear();

    // add several entries
    _hostInterfaces.Add( ... );

    // restore saved to HostInterfaceSelected 
    if (saveSelected != null)
        HostInterfaceSelected = _hostInterfaces.FirstOrDefault(s => s.Name == saveSelected.Name && s.Address != null && s.Address.Equals(saveSelected.Address));