wpf - WPF-Prism CanExecute方法未调用

我正在用两个TextBox(用户名和密码)和一个Login按钮编写一个简单的登录UserControl。我希望仅在填写用户名和密码字段时才启用“登录”按钮。我正在使用Prism和MVVM。 LoginViewModel包含一个名为LoginCommand的属性，该属性绑定(bind)到Login按钮。我的ViewModel中有一个CanLoginExecute()方法，但仅在应用程序启动时才会触发，然后再也不会触发。因此，永远不会启用“登录”按钮。我想念什么？

这是我的xaml:

<TextBox x:Name="username"
    Text="{Binding Path=Username, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
<TextBox x:Name="password"
    Text="{Binding Path=Password, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}" />
<Button Content="Login"
    cmnd:Click.Command="{Binding LoginCommand}" />

这是我的ViewModel

class LoginViewModel : IDataErrorInfo, INotifyPropertyChanged
{
    public LoginViewModel()
    {
        this.LoginCommand =
            new DelegateCommand<object>(
                this.LoginExecute, this.CanLoginExecute);
    }

    private Boolean CanLoginExecute(object dummyObject)
    {
        return (string.IsNullOrEmpty(Username) ||
                string.IsNullOrEmpty(Password)) ? false : true;
    }

    private void LoginExecute(object dummyObject)
    {
        if (CheckCredentials(Username, Password))
        {
            ....
        }
    }

    #region IDataErrorInfo Members

    public string Error
    {
        get { throw new NotImplementedException(); }
    }

    public string this[string columnName]
    {
        get
        {
            string result = null;
            if (columnName == "Username")
            {
                if (string.IsNullOrEmpty(Username))
                    result = "Please enter a username";
            }
            else if (columnName == "Password")
            {
                if (string.IsNullOrEmpty(Password))
                    result = "Please enter a password";
            }
            return result;
        }
    }

    #endregion // IDataErrorInfo Members

    #region INotifyPropertyChanged Members

    public event PropertyChangedEventHandler PropertyChanged;

    void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

    #endregion // INotifyPropertyChanged Members

    #region Properties

    private String _username;
    public String Username
    {
        get { return _username; }
        set
        {
            if (value == _username)
                return;
            _username = value;
            this.OnPropertyChanged("Username");
        }
    }

    private String _password;
    public String Password
    {
        get { return _password; }
        set
        {
            if (value == _password)
                return;
            _password = value;
            this.OnPropertyChanged("Password");
        }
    }

    public ICommand LoginCommand { get; private set; }

    #endregion // Properties
}

最佳答案

绑定(bind)控件很可能永远不会再询问CanExecute状态。每当您检测到更改命令的CanExecute状态的条件时，就需要在DelegateCommand上调用 RaiseCanExecuteChanged 方法。这向绑定(bind)的控件发出信号以更新CanExecute状态。

关于wpf - WPF-Prism CanExecute方法未调用，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/2444927/