WPF MVVM 文本框绑定

Question

更新

我可以使用这个自定义实现 here。使用 prism 时存在弱引用问题。

我是 MVVM 和 Microsoft 的 Prism 的新手。我正在尝试让我的文本框绑定正常工作。如果文本框不为空，登录按钮应该可用。 setter 正在工作，但 CanOnLogin() 总是 returns false。

型号

class UserModel
{
    private string userName;
    private string passWord;
    public string UserName
    {
        get { return userName; }
        set { userName = value; }
    }


    public string PassWord
    {
        get { return passWord; }
        set { passWord = value; }
    }
}

ViewModel

class LoginViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private UserModel user;
    private DelegateCommand _loginCommand;
    public UserModel User 
    { 
        get { return user; }
        set { user = value; }
    } 

    public string UserName
    {
        get { return user.UserName; }
        set
        {
            user.UserName = value;
            OnPropertyChanged("UserName");
        }
    }

    public ICommand LoginCommand
    {
        get { return _loginCommand; }
    }

    public LoginViewModel() 
    {
        _loginCommand = new DelegateCommand(OnLogin, CanOnLogin);
        //implement CanOnLoginChanged here?
        user = new UserModel();
    }

    private bool CanOnLogin()
    {
        if (String.IsNullOrEmpty(user.UserName))
        {
            return false;
        }
        else 
        {
            return true; 
        }
    }

    private void OnLogin() 
    {
    // Do something here
        MessageBox.Show(user.UserName);
    }

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

    public event EventHandler CanOnLoginChanged
    {
        add
        {
            CommandManager.RequerySuggested += value;
        }
        remove
        {
            CommandManager.RequerySuggested -= value;
        }
    }
}

查看

<TextBox Name="username" Text="{Binding Path=UserName, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" HorizontalAlignment="Center" Margin="10" Width="175" Grid.Row="1" Grid.Column="0" Controls:TextBoxHelper.Watermark="Username" Controls:TextBoxHelper.ClearTextButton="True"/>
<Button HorizontalAlignment="Center" Margin="10" Width="87.5" Grid.Row="3" Grid.Column="0" Command="{Binding LoginCommand}">Login</Button>

代码隐藏

public partial class LoginView : MetroWindow
{
    public LoginView()
    {
        InitializeComponent();
        DataContext = new LoginViewModel();
    }
}

Answer 1

问题是您必须创建 canExecuteChanged：现在可以使用了。

 public event EventHandler CanExecuteChanged {
        add {
            CommandManager.RequerySuggested += value;
        }
        remove {
            CommandManager.RequerySuggested -= value;
        }
    }

can execute 将检查是否有任何相关事件可以更改状态，如果找到，会将状态从 false 更改为 true。

Answer 2

我相信您没有将对象参数作为参数传递给 OnLogin 和 CanOnLogin，这就是为什么它对我不起作用它确实如此并且在任何属性或方法而不是我所做的地方实现 canOnLogInChanged ，或者只是获取此代码并重试：

using System;
using System.Windows.Input;
class LoginViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private UserModel user;
    private DelegateCommand _loginCommand;
    public UserModel User
    {
        get { return user; }
        set { user = value; }
    }

    public string UserName
    {
        get { return user.UserName; }
        set
        {
            user.UserName = value;
            OnPropertyChanged("UserName");
        }
    }

    public ICommand LoginCommand
    {
        get { return _loginCommand; }
    }

    public LoginViewModel()
    {
        _loginCommand = new DelegateCommand(OnLogin, CanOnLogin);
        //implement CanOnLoginChanged here?
        user = new UserModel();
    }

    private bool CanOnLogin(object parameter)
    {
        if (String.IsNullOrEmpty(user.UserName))
        {
            return false;
        }
        else
        {
            return true;
        }
    }
    public event EventHandler CanOnLoginChanged
    {
        add
        {
            CommandManager.RequerySuggested += value;
        }
        remove
        {
            CommandManager.RequerySuggested -= value;
        }
    }
    private void OnLogin(object parameter)
    {
        // Do something here
        MessageBox.Show(user.UserName);
    }

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


}

Answer 3

在 CanOnLogin 中，您应该检查来自 ViewModel 的属性，属性Changed 可以工作：

String.IsNullOrEmpty(UserName)

如果这没有帮助，请尝试将您的命令设置为延迟加载，以确保首先正确初始化所有数据。像

public ICommand LoginCommand
{
    get { return _loginCommand ?? (_loginCommand = new DelegateCommand(OnLogin, CanOnLogin)); }
}

或更改 LoginViewModel() 中的初始化顺序：

user = new UserModel();
_loginCommand = new DelegateCommand(OnLogin, CanOnLogin);

你是对的：Prism 委托命令并不总是像我期望的那样工作。报道here。

检查此 Example 自定义实现。

希望对您有所帮助！

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