Return to viewmodel 禁用可执行命令 (Caliburn Micro - Windows Phone 8.1)

Posted 2023-04-12

【中文标题】Return to viewmodel 禁用可执行命令 (Caliburn Micro - Windows Phone 8.1)

【英文标题】：Return to viewmodel disables canexcute of commands (Caliburn Micro - Windows Phone 8.1)

【发布时间】：2017-08-02 02:24:02

【问题描述】：

我第一次使用适用于 Windows Phone 8.1 的 Caliburn Micro。

我正在使用带有命令的按钮按约定进行绑定，该命令在我的视图模型中执行一个方法，其中它有一个“CanExecute”。到目前为止一切顺利，但是当我登录（此按钮的方法）并返回（注销）到我的登录视图时，我的登录屏幕上所有按钮的命令都停止工作（我相信问题出在 CanExecute ），然后无需退出应用程序并返回即可登录。

以下是用于登录和注销的方法及其“可执行”。

登录（在 LoginViewModel.cs 中）：

public async void LoginCommand()

     var retorno = await _loginService.LoginAsync(Usuario, Senha);
     if (retorno.User != null)
     
         Ambiente.Instance.Configuracao.Configurar(retorno.User);
         Ambiente.Instance.Carregar();

         DefinirEstadoInicial();
         navigationService.NavigateToViewModel(typeof(HomeViewModel));
     
     ...


public bool CanLoginCommand

     get  return !string.IsNullOrEmpty(Usuario) && !string.IsNullOrEmpty(Senha); 



private string _usuario;

public string Usuario

     get  return _usuario; 
         set
     
         _usuario = value;
         NotifyOfPropertyChange();
         NotifyOfPropertyChange(() => CanLoginCommand);
     


private string _senha;

public string Senha

     get  return _senha; 

     set
     
          _senha = value;
          NotifyOfPropertyChange();
          NotifyOfPropertyChange(() => CanLoginCommand);
     

注销（在 HomeViewModel.cs 中）

public async void SairCommand()

     await MessageBox("Deseja fazer logout do aplicativo?", "Logout", textoBotaoEsquerda: "Não", codeBotaoDireita: new System.Action(() =>
     
          Ambiente.Instance.Recarregar();
          navigationService.NavigateToViewModel(typeof(LoginViewModel));
     ), textoBotaoDireita: "Sim");

LoginView.xaml

<StackPanel Margin="0,30,0,0" Name="StackLogin">
            <Image Source="ms-appx:///Assets/Images/[e-mail]" MaxWidth="240" Stretch="UniformToFill" />
            <TextBlock Text="Login" Margin="0,50,0,0" Style="StaticResource PageTitle"/>
            <TextBlock Text="Use sua conta Muambator/Pacotes para continuar rastreando suas encomendas"
                       Margin="0,20,0,0"
                       TextWrapping="Wrap" Style="StaticResource PageDescription" HorizontalAlignment="Center" />
            <Border Background="White" Margin="0,30,0,0" CornerRadius="3" MaxWidth="320">
                <Grid VerticalAlignment="Center">
                    <Grid.RowDefinitions>
                        <RowDefinition Height="Auto"/>
                        <RowDefinition Height="Auto"/>
                    </Grid.RowDefinitions>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="Auto"/>
                        <ColumnDefinition Width="*"/>
                    </Grid.ColumnDefinitions>
                    <Image Source="ms-appx:///Assets/Images/[e-mail]" Margin="10,0,0,0" Width="20" />
                    <TextBox Grid.Column="1" Text="Binding Path=Usuario, Mode=TwoWay" PlaceholderText="LOGIN" Style="StaticResource LoginTextBox"/>
                    <Border Grid.ColumnSpan="2" BorderBrush="LightGray" BorderThickness="0,0,0,1" />
                    <Image Grid.Row="1" Source="ms-appx:///Assets/Images/[e-mail]" Margin="10,0,0,0" Width="20" />
                    <PasswordBox Grid.Row="1" Grid.Column="1" x:Name="Senha" PlaceholderText="SENHA" Style="StaticResource LoginPasswordBox" VerticalAlignment="Center" />
                    <Button Click="MostrarEsqueciMinhaSenhaCommand_Click"
                            x:Name="MostrarEsqueciMinhaSenhaCommand"
                            Grid.Row="1"
                            Grid.Column="1"
                            Width="50" 
                            Style="StaticResource EsqueciMinhaSenhaButtonStyle"
                            HorizontalAlignment="Right"/>                    
                </Grid>
            </Border>

            <Button x:Name="LoginCommand" Width="322" Height="40" Margin="0,20,0,0" HorizontalAlignment="Stretch" Background="#6EAF2D" BorderThickness="0" Style="StaticResource ButtonStyle" >
                <Grid>
                    <TextBlock Style="StaticResource ButtonText">ENTRAR</TextBlock>
                    <Image Margin="20,0,-75,0" Height="15" Source="ms-appx:///Assets/Images/[e-mail]" />
                </Grid>
            </Button>
        </StackPanel>

更新 1：

视图模型从“Screen”和“INotifyPropertyChangedEx”继承和实现

【参考方案1】：

LoginView.xaml 的代码隐藏中有一行导致问题，只需删除该行，一切正常。

This.NavigationCacheMode = NavigationCacheMode.Required;