Question

我是xaml，WPF，C＃和MVVM范例的新手。我已经开始使用基于this example project的应用程序，在选定的摘录中我想在单击身份验证按钮后从LoginPageViewModel中禁用身份验证按钮（如果您通过身份验证，则没有点击按钮）。我有命令绑定工作，以及视图和ViewModel之间的文本控制绑定。我的LoginPageViewModel基于一个继承自INotifyPropertyChanged的抽象类

setter AuthenticateButtonEnabled正在运行，但它没有绑定到表单上的isEnabled proprerty。我的问题是，我可以错过什么，以及如何跟踪View和ViewModel之间的绑定？

LoginPageView.xaml按钮：

        <Button x:Name="authenticateButton" Content="{x:Static res:Strings.LoginPage_authenticateButton_content}" 
            Grid.Column="2" Margin="53,4,0,10" 
            Grid.Row="2" FontSize="16" 
            IsEnabled="{Binding Path=AuthenticateButtonEnabled}"
            Command="{Binding Path=AuthenticateCommand}" HorizontalAlignment="Left" Width="87"/>

viewModel

    private String _username;
    private String _responseTextBlock;
    private String _linkTextBlockURI;
    private String _linkTextBlockText;
    private bool _authenticateButtonEnabled;
    ...
    private async void Authenticate()
    {
        ResponseTextBlock = Strings.LoginPage_responseBlock_content_checking;#this works!
        AuthenticateButtonEnabled = false;
        return;

    }
    ....

    public bool AuthenticateButtonEnabled 
    {
        get { return _authenticateButtonEnabled; }
        set { _authenticateButtonEnabled = value;  OnPropertyChanged("AuthenticateButtonEnabled"); }
    }
    // this is in the abstract class.
    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = this.PropertyChanged;
        if (handler != null)
            handler(this, new PropertyChangedEventArgs(propertyName));
    }

Answer 1

如果将Button的命令属性绑定到Viewmodel中的ICommand属性，则不需要处理Button的IsEnabled属性，因为它由ICommand实现的CanExecute方法处理。

google for RelayCommand或DelegateCommand

Answer 2

如果你想同时拥有：command和AuthenticateButtonEnabled，那么只需在CanExecute委托中检查此属性，然后在属性setter update命令中检查。

以下是DelegateCommand的实施以及您可能会觉得有用的一些改进：

bool _isAuthenticateButtonEnabled;
public bool IsAuthenticateButtonEnabled 
{
    get { return _isAuthenticateButtonEnabled; }
    set
    {
        _isAuthenticateButtonEnabled = value;
        OnPropertyChanged();
        AuthenticateCommand.Update();
    }
}

// the base could class could actually implement this
void OnPropertyChanged([CallerMemberName] string property) => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(property));

public DelegateCommand AuthenticateCommand { get; }

// view model constructor
public ViewModel()
{
    AuthenticateCommand = new DelegateCommand(o =>
    {
       ... // some actions when command is executed
    }, o =>
    {
       bool somecondition = ...; // some condition to disable button, e.q. when executing command
       return somecondition && IsAuthenticateButtonEnabled;
    });
}

这将让你拥有：property to enable / disable按钮，可以用于绑定（到另一个控件，例如CheckBox.IsChecked）和命令，当命令不应该时，可以有独立条件来禁用按钮执行一个长时间运行的命令时，执行（通常在async命令委托中执行;但为此，您可能需要检查this回答。）。

Answer 3

感谢海报的帮助，我想与他人分享工作解决方案。我使用了DelegateCommand，但是必须更改loginPageViewModel中的一些部分才能使它工作：我还更新了xaml，以便在成功验证后控件都处于非活动状态。

loginPage xaml：

    <Label x:Name="usernameLabel"  Content="{x:Static res:Strings.LoginPage_usernameLabel_content}" HorizontalAlignment="Left" Margin="10,4,0,0" Grid.Row="0" VerticalAlignment="Top" Width="130" FontSize="16"  Height="36" Grid.Column="1"/>
    <TextBox x:Name="usernameTextBox" Grid.Column="2" Grid.Row="0" TextWrapping="Wrap" 
             Text="{Binding Username, UpdateSourceTrigger=PropertyChanged}" 
             IsEnabled="{Binding AuthenticateButtonEnabled}"
             Margin="10,5,0,6" FontSize="16" HorizontalAlignment="Left" Width="130" TextChanged="usernameTextBox_TextChanged"/>
    <Label x:Name="passwordLabel" Content="{x:Static res:Strings.LoginPage_passwordLabel_content}" Margin="10,5,0,0" Grid.Row="1" VerticalAlignment="Top" FontSize="16" Height="36" Grid.RowSpan="2" HorizontalAlignment="Left" Width="130" Grid.Column="1"/>
    <PasswordBox x:Name="passwordBox" Grid.Column="2" Margin="10,0,0,9" 
        PasswordChanged="PasswordBox_PasswordChanged"
        IsEnabled="{Binding AuthenticateButtonEnabled}"
        Grid.Row="1" FontSize="16" HorizontalAlignment="Left" Width="130"/>
    <Button x:Name="authenticateButton" Content="{x:Static res:Strings.LoginPage_authenticateButton_content}" 
            Grid.Column="2" Margin="53,4,0,10" 
            Grid.Row="2" FontSize="16" 
            IsEnabled="{Binding AuthenticateButtonEnabled}"
            Command="{Binding Path=AuthenticateCommand}" HorizontalAlignment="Left" Width="87"/>

loginPageViewModel：

    ....
    private bool _authenticateButtonEnabled;
    private DelegateCommand _authenticateCommand;
    public bool AuthenticateButtonEnabled {
        get { return _authenticateButtonEnabled; }
        set
        {
            _authenticateButtonEnabled = value;
            DynamicOnPropertyChanged(); // this is so named to not content with onPropertyChanged defined elsewhere.
            AuthenticateCommand.Update();
        }
    }
    ...

    public DelegateCommand AuthenticateCommand
    { 
        get {
            if (_authenticateCommand == null)
            {
                _authenticateCommand = new DelegateCommand(Authenticate, AuthenticateEnded);
            }
            return _authenticateCommand;
        }
    }
    private bool AuthenticateEnded(object obj) {
        return _authenticateButtonEnabled;
    }
    private async void Authenticate(object obj)
    {
        AuthenticateButtonEnabled = false;

        ResponseTextBlock = Strings.LoginPage_responseBlock_content_checking;
        i3SoftHttpClient _httpClient = new i3SoftHttpClient();
        i3SoftUser _i3SoftUser;
        AuthenticateCommand.CanExecute(false);
        ....
      // if authentication does not succeed - turn the buttons back on.
        AuthenticateCommand.CanExecute(true);
     }

和我添加的Delegate command class：

    public void Update()
    {
        if (CanExecuteChanged != null)
            CanExecuteChanged(this, EventArgs.Empty);
    }

错误绑定isEnabled到xaml中的按钮

3 个答案: