将TextBlock的可见性绑定到TextBox

Question

我试图根据他们选择的用户名是否可用来绑定TextBlock的Visibility 。 这是TextBlock的XAML：

<TextBlock Grid.Row="5" Text="* Username already taken" Visibility="{Binding UsernameAvailable, Converter={StaticResource BoolToVis}}" Margin="5"/>

它绑定到的属性，并且激发的命令是：

public bool UsernameAvailable { get; set; }

#region RegisterCommand

private DelegateCommand _registerCommand;
public ICommand RegisterCommand
{
    get
    {
        _registerCommand = new DelegateCommand(param => Register());
        return _registerCommand;
    }
}

private void Register()
{
    if (IsPasswordValid())
    {
        var newUser = new User
        {
            FirstName = _firstName,
            LastName = _lastName,
            Username = _userName,
            Password = _password //TODO: Hashing of password
        };
        using (var context = new WorkstreamContext())
        {
            var users = context.Set<User>();
            users.Add(newUser);
            context.SaveChanges();
        }
    }
    else
    {
        UsernameAvailable = true; // TODO: Display TextBlock correctly
        MessageBox.Show("Failed"); // TODO: Correctly show messages displaying what is incorrect with details
    }
}

public bool IsPasswordValid()
{
    return FirstName != string.Empty &&
            LastName != string.Empty &&
            UserName != string.Empty &&
            Password.Any(char.IsUpper);
}

#endregion

将显示MessageBox，但不会出现TextBlock 。 当我检查Register方法中是否已经使用了用户名时，如何确保显示TextBlock ？

Answer 1

您必须阅读有关INotifyPropertyChanged的信息，实现此接口，然后将UsernameAvailable属性修改为：

private usernameAvailable

public bool UsernameAvailable 
{ 
    get
    {
        return usernameAvailable;
    }
    set
    {
        if (usernameAvailable != value)
        {
            usernameAvailable = value;
            OnPropertyChanged(nameof(UsernameAvailable));
        }
    }
}

在这里，您可以找到INotifyPropertyChanged实现示例。