无法获得我按钮的IsEnabled状态更改

Question

我已经尝试了很多方法来使它正常工作，但是我显然很想念something，因为无论我做什么，我的“ Register”按钮都被启用了[[not 。

在我的XAML中：

<Button Text="Register" 
        Style="{StaticResource RegularButtonStyle}" 
        WidthRequest="280"
        x:Name="RegisterButton">
    <!-- I HAD the following, but it wasn't working so I finally decided to try DataTriggers -->
    <!-- bindings:Bi.nd="Clicked RegisterButtonClickedCommand;IsEnabled IsRegisterButtonEnabled"> -->
    <Button.Triggers>
        <DataTrigger TargetType="Button"
                     Binding="{Binding IsRegisterButtonEnabled}"
                     Value="False">
            <Setter Property="IsEnabled" Value="False"></Setter>
        </DataTrigger>
        <DataTrigger TargetType="Button"
                     Binding="{Binding IsRegisterButtonEnabled}"
                     Value="True">
            <Setter Property="IsEnabled" Value="True"></Setter>
        </DataTrigger>
    </Button.Triggers>
</Button>

在ViewModel中：
public class RegisterViewModel : MvxViewModel
{
    ...

    private bool _isRegisterButtonEnabled;
    public bool IsRegisterButtonEnabled
    {
        get => ShouldEnableRegisterButton();

        set
        {
            _isRegisterButtonEnabled = value;
            SetProperty(ref _isRegisterButtonEnabled, value);
        }
    }

    ...
    public IMvxCommand RegisterButtonClickedCommand { get; private set; }
    ...

    private void InitializeCommands()
    {
        ...
        RegisterButtonClickedCommand = new MvxCommand(RegisterUser);
    }

    ...

    private bool ShouldEnableRegisterButton()
    {
        var isValidUser = _userName.Validate();
        var isValidPass = _password.Validate();
        var isValidConfirmedPass = _confirmedPassword.Validate();

        var shouldEnable = isValidUser && isValidPass && isValidConfirmedPass;

        _mvxLogger.Log(MvxLogLevel.Trace, () => $"RegisterViewModel : ShouldEnableRegisterButton() called. Returning: {shouldEnable}");

        return shouldEnable;
    }

    ...
}

我已经阅读了MvvmCross“ Documentation”，但这全是对话式的，我找不到任何足够具体的绑定按钮的IsEnabled属性的特定示例，可以带我到那里。 
肯定会得到一些帮助。 ：）
客房部信息：我正在使用以下NuGet软件包（/库）

MvvmCross和MvvmCross.Forms v6.3.1
• Xamarin.Forms v4.0.0.497661
• Xamarin.Android。*库均为v28.0.0.1

然后以为我应该更新，因为有可用的更新，所以我更新到以下内容；

MvvmCross和MvvmCross.Forms v6.4.1

Xamarin.Forms v4.2.0.848062

Xamarin.Android。*库现在都是v28.0.0.3

还对共享的东西使用.Net Standard v2.0.3。

Answer 1

您可以尝试以下方法：

public class RegisterViewModel : INotifyPropertyChanged
{

    public event PropertyChangedEventHandler PropertyChanged;
    private bool _isRegisterButtonEnabled;

    public bool IsRegisterButtonEnabled
    {
        set { _isRegisterButtonEnabled = value; PropertyChanged?.Invoke(this, new 
        PropertyChangedEventArgs(nameof(IsRegisterButtonEnabled))); }
        get { return _isRegisterButtonEnabled; }
    }
}

然后在Xaml中
<Button Text="Register" 
        Style="{StaticResource RegularButtonStyle}" 
        IsEnabled = "{Binding IsRegisterButtonEnabled}"
        WidthRequest="280"
        x:Name="RegisterButton">
</Button>

Answer 2

最终答案原来是问题的组合，而其中一个大问题可能需要在SO上发表新的帖子/问题。

所以这就是最终的工作；

我将Xaml更新为以下内容；

<Button Text="Register" 
        Style="{StaticResource RegularButtonStyle}" 
        WidthRequest="280"
        x:Name="RegisterButton"
        Command="{Binding RegisterButtonClickedCommand}">
    <Button.Triggers>
        <DataTrigger TargetType="Button"
                     Binding="{Binding IsRegisterButtonEnabled}"
                     Value="False">
            <Setter Property="IsEnabled" Value="False"></Setter>
        </DataTrigger>
        <DataTrigger TargetType="Button"
                     Binding="{Binding IsRegisterButtonEnabled}"
                     Value="True">
            <Setter Property="IsEnabled" Value="True"></Setter>
        </DataTrigger>
    </Button.Triggers>
</Button>

还将RegisterViewModel.cs更新为以下内容；
public class RegisterViewModel : MvxViewModel, INotifyPropertyChanged
{
    ...

    // Added this (and the inheriting from INotify.. [per @Adlorem]
    public event PropertyChangedEventHandler PropertyChanged;

    private bool _isRegisterButtonEnabled;
    public bool IsRegisterButtonEnabled
    {
        get
        {
            _mvxLogger.Log(MvxLogLevel.Trace,
                () => $"RegisterViewModel : IsRegisterButtonEnabled property get called. Returning: {_isRegisterButtonEnabled}");

            return _isRegisterButtonEnabled;
        } 

        set
        {
            _isRegisterButtonEnabled = value;

            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(IsRegisterButtonEnabled)));

            _mvxLogger.Log(MvxLogLevel.Trace,
                () => $"RegisterViewModel : IsRegisterButtonEnabled property set called. value: {value}");

        }
    }

    ...

    private bool ShouldEnableRegisterButton()
    {
        var isValidUser = _userName.Validate();
        var isValidPass = _password.Validate();
        var isValidConfirmedPass = _confirmedPassword.Validate();

        var shouldEnable = isValidUser && isValidPass && isValidConfirmedPass;

        // Must set this or the PropertyChanged definitely won't fire!
        IsRegisterButtonEnabled = shouldEnable;

        _mvxLogger.Log(MvxLogLevel.Trace,
            () => $"RegisterViewModel : ShouldEnableRegisterButton() called. Returning: {shouldEnable}");

        return shouldEnable;
    }

    ...
}

显然，这不是最佳选择。 MvvmCross的SetProperty()应该触发PropertyChanged事件，由于某种原因，它不会触发。