c# - View 模型的可见性不起作用

Question

我有一个带有登录 View 模型的登录 View ，遇到了一个让我抓狂的问题。请注意，我使用的是 MVVM Light。

在 View 模型中，我有三个可见性属性，它们应该根据 View 模型的状态隐藏 View 中的元素。

我的属性如下所示，所有属性都触发 PropertyChangedEvent:

public Visibility ErrorPanelVisibility
public Visibility LoginPanelVisibility
public Visibility LoadingPanelVisibility

绑定(bind)看起来像这样(省略边距等):

<Border Visibility="{Binding ErrorPanelVisibility}">
<StackPanel Visibility="{Binding LoginPanelVisibility}">
<StackPanel Visibility="{Binding LoadingPanelVisibility}">

当用户按下登录按钮时，在 View 模型中执行此方法的命令会更改可见性:

private void ExecuteLogin()
{
    ErrorPanelVisibility = Visibility.Collapsed;
    LoginPanelVisibility = Visibility.Collapsed;
    LoadingPanelVisibility = Visibility.Visible;

    // This method takes a few seconds to complete.
    Login(errorMessage =>
            {
                if (!String.IsNullOrEmpty(errorMessage))
                {
                    ErrorMessage = errorMessage;

                    ErrorPanelVisibility = Visibility.Visible;
                    LoginPanelVisibility = Visibility.Visible;
                    LoadingPanelVisibility = Visibility.Collapsed;
                }
                else
                {
                    DialogResult = true;
                }
            });
}

问题是面板没有被折叠或更改为在 View 中可见，更改没有反射(reflect)在 View 中。当我将可见性设置为可见但未折叠时，PropertyChangedEvent 被触发并且 ErrorPanel 正在工作。

编辑:登录方法:

private void Login(Action<string> callback)
{           
    string errorMessage = string.Empty;

    if (SelectedServer == null)
    {
        errorMessage = "Select server."; //TODO: Translate
    }
    else if (String.IsNullOrEmpty(Username) || String.IsNullOrEmpty(Password))
    {
        errorMessage = Resources.WrongUsernameOrPassword;
    }
    else
    {
        try
        {
            // Changed name due to customer information
            IWCFClient wcfClient = WCFClient.GetInstance(); 

            LoginObj loginObj = wcfClient.Login(Username, Password);

            // Removed some cases to simplify, they all set the errorMessage.
            switch (loginObj.LoginStatus)
            {
                case LoginObj.LoginState.AlreadyLogedin:
                    errorMessage = Resources.UserAlreadyLoggedOn;
                    break;
                default:
                    errorMessage = Resources.ErrorOccurred;
                    break;    
            }                
        }
        catch (Exception e)
        {
            errorMessage = e.Message;
        }
    }
    callback(errorMessage);
}

但是，如果我将我的代码更改为这样，面板可以工作:

bool login = false;
private void ExecuteLogin()
{
    if (login)
    {
        ErrorPanelVisibility = Visibility.Collapsed;
        LoginPanelVisibility = Visibility.Collapsed;
        LoadingPanelVisibility = Visibility.Visible;
    }
    else
    {
        ErrorPanelVisibility = Visibility.Visible;
        LoginPanelVisibility = Visibility.Visible;
        LoadingPanelVisibility = Visibility.Collapsed;
    }

    login = !login;
}

这里有没有明显的错误，或者有人能找出我做错了什么吗？

Answer 1

还有。我建议您避免在 ViewModel 中使用 UI 类型。尝试使用 bool 值并使用 BoolToVisibilityConverter。

附言确保为控件设置 DataContext。