WPF MVVM：如何将按钮文本绑定到LINQ表达式并动态更新？

我尝试将按钮文本绑定到LINQ表达式，初始代码如下：

public string CloseButtonText => Roles.Any(r => r.IsChanged) ? "Save and close" : "Close";

程序启动时文本显示正常，但当RoleViewModel对象的属性发生变化时，按钮文本无法动态更新。

现有架构代码 #

RoleSelectionViewModel类 #

public class RoleSelectionViewModel : ViewModelBase
{
    public RoleSelectionViewModel()
    {
        LoadRoles();
    }
    
    private readonly ObservableCollection<RoleViewModel> _roles = [];
    public IList<RoleViewModel> Roles => _roles;

    public string CloseButtonText => Roles.Any(r => r.IsChanged) ? "Save and close" : "Close";

    private void LoadRoles()
    {
        // 避免设计时读取XML角色导致崩溃
        if (DesignerProperties.GetIsInDesignMode(new System.Windows.DependencyObject()))
        {
            return;
        }

        var roles = [ .. RolesManagement.ReadRolesXml().OrderBy(r => r.RoleName), ];
        roles.ForEach(r => Roles.Add(new RoleViewModel(r)));
    }
    // 类的其他部分...
}

RoleViewModel类 #

public class RoleViewModel : ViewModelBase
{
    public RoleViewModel() { }

    public RoleViewModel(Role role) => Role = role;

    public Role Role { get; protected set; }

    public int RoleId => Role.RoleId;

    public string RoleName => Role.RoleName;

    public string Name
    {
        get { return Role.IssuedBy; }
        set
        {
            Role.IssuedBy = value;
            OnPropertyChanged();
        }
    }

    public string Department
    {
        get { return Role.Department; }
        set
        {
            Role.Department = value;
            OnPropertyChanged();
        }
    }

    public string Email
    {
        get { return Role.Email; }
        set
        {
            Role.Email = value;
            OnPropertyChanged();
        }
    }
    // 其他属性...
}

ViewModelBase类 #

public class ViewModelBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private bool _isChanged = false;
    public bool IsChanged
    {
        get { return _isChanged; }
        set
        {
            _isChanged = value;
            OnPropertyChanged();
        }
    }

    protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        if (propertyName != nameof(IsChanged))
        {
            IsChanged = true;
        }
    }
}

XAML按钮绑定代码 #

<Button
    x:Name="Close_Button"
    Width="96"
    Height="30"
    Padding="10,0,10,0"
    Background="#FF838383"
    Foreground="White"
    Command="{Binding CloseCommand}"
    >
    <TextBlock
        x:Name="Close_Button_Text"
        Text="{Binding CloseButtonText}"
        />
</Button>

尝试的解决方法及问题 #

1. 手动订阅RoleViewModel.PropertyChanged事件

foreach (var role in Roles)
{
    role.PropertyChanged += Role_PropertyChanged;
}

private void Role_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    if (e.PropertyName == nameof(RoleViewModel.IsChanged))
    {
        this.OnPropertyChanged(nameof(CloseButtonText));
    }
}

问题：Role_PropertyChanged方法仅在点击关闭按钮时触发，而非角色属性变化时。

2. 订阅ObservableCollection的CollectionChanged事件

public string CloseButtonText { get; set; } = "Close";

private void LoadRoles()
{
    _roles.CollectionChanged += Roles_CollectionChanged;
    // 方法其余代码不变
}

private void Roles_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
{
    if (e.OldItems != null)
    {
        foreach (RoleViewModel item in e.OldItems)
        {
            item.PropertyChanged -= Role_PropertyChanged;
        }
    }
    if (e.NewItems != null)
    {
        foreach (RoleViewModel item in e.NewItems)
        {
            item.PropertyChanged += Role_PropertyChanged;
        }
    }
}

private void Role_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    if (sender is RoleViewModel role 
        && role.IsChanged 
        && e.PropertyName == nameof(RoleViewModel.IsChanged))
    {
        CloseButtonText = "Save and close";
        this.OnPropertyChanged(nameof(CloseButtonText));
    }
}

问题：仍然无效，Role_PropertyChanged还是仅在点击关闭按钮时触发。

最终解决方案 #

无法直接通过绑定LINQ表达式实现动态更新，需通过以下两步修复：

• 在每个绑定Role属性的TextBox中添加UpdateSourceTrigger=PropertyChanged（默认触发时机为TextBox失去焦点，导致属性变更事件延迟触发）
• 保留对ObservableCollection的CollectionChanged事件订阅，以及每个RoleViewModel的PropertyChanged事件订阅，确保角色集合变化或单个角色属性变化时，都能通知CloseButtonText更新。

内容的提问来源于stack exchange，提问作者kglundgren