WPF 命令绑定的各种方式

WPF 命令绑定的各种方式

引言

在WPF开发过程中，不得不学习的就是MVVM模式。但是在MVVM中又绕不开命令（Command）的使用。下面通过几种方式介绍我了解的WPF命令绑定方式。

如何使用

控件继承ICommand接口，直接使用Command

首先通过这里简单介绍Command在MVVM中的使用。

ViewModel类

// using System.ComponentModel;
// using System.Runtime.CompilerServices;

MainViewModel

	/// 

    /// Interactive logic for MainWindow
    /// 
    public class MainViewModel : INotifyPropertyChanged
    {
        public MainViewModel()
        {
            SignInCommand = new RelayCommand(() =>
            {
                MessageBox.Show($"Hello {Username},welcome to Melphily's world");
            });
        }
        private string username;

        /// 

        /// User name
        /// 
        public string Username
        {
            get { return username; }
            set
            {
                username = value;
                RaisePropertyChanged();
            }
        }

        /// 

        /// Sign in command
        /// 
        public ICommand SignInCommand { get; private set; }

        #region Notify Handler

        public event PropertyChangedEventHandler PropertyChanged = (sender, e) => { };

        public void RaisePropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }

        #endregion
    }

Command类

// using System.Windows.Input;

RelayCommand

    /// 

    /// the command without input parameter
    /// 
    public class RelayCommand : ICommand
    {
        public event EventHandler CanExecuteChanged = (sender, e) => { };

        private Action mAction;

        public RelayCommand(Action action)
        {
            this.mAction = action;
        }

        public bool CanExecute(object parameter)
        {
            // Always allow the action can execute.
            return true;
        }

        public void Execute(object parameter)
        {
            // Take action
            mAction.Invoke();
        }
    }

View类

MainWindow.xaml

MainWindow.xaml.cs

	/// 

    /// Interactive logic for MainWindow.xaml
    /// 
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            // Bind the Binding source to the DataContext
            DataContext = new MainViewModel();
        }
    }
    

至此，MVVM的简单应用就完成了。这里面简单实现了输入用户名登陆，在登陆（Sign In）操作时，使用了命令绑定的形式****，在ViewModel类（MainViewModel）接收命令，并做相应的处理。

运行效果：

扩展使用

上面通过较为完整的实例展示了MVVM模式中的Command绑定使用。但是一些WPF控件（例如ListBox）并不支持Command命令绑定。下面我们通过几种方式讨论如何解决，以ListBox举例。

使用InputBinding

Model

MusicItemModel.cs

public class MusicItemModel
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Singer { get; set; }

        public MusicItemModel()
        {
            SelectedCommand = new RelayCommandWithParameter(p =>
            {
                MessageBox.Show($"Selected music is {Name} Singed by {Singer},the Id is {p}");
            });
        }

        /// 

        /// Select command
        /// 
        public ICommand SelectedCommand { get; private set; }

    }

Command

RelayCommandWithParameter.cs

	/// 

    /// the command without input parameter
    /// 
    public class RelayCommandWithParameter : ICommand
    {
        public event EventHandler CanExecuteChanged = (sender, e) => { };


        private Action