WPF 笔记 八 命令

好处：从不同 的UI实现同一个功能。

例子1：为按钮绑定系统预定义Command

    <Window.CommandBindings>
        <CommandBinding Command="ApplicationCommands.New" Executed="CommandBinding_Executed" CanExecute="CommandBinding_CanExecute"/>
    </Window.CommandBindings>
    <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
        <Button Command="ApplicationCommands.New">New</Button>
    </StackPanel>

注意：上面代码的等效代码，在WIndow初始化时，

private void CreateNewCommandBinding()
{
    //后台代码创建命令绑定：1)添加绑定到窗口
    //创建绑定
    CommandBinding binding = new CommandBinding(ApplicationCommands.New);
    //添加事件处理
    binding.Executed += CommandBinding_Executed;
    binding.CanExecute += CommandBinding_CanExecute;
    //注册
    this.CommandBindings.Add(binding);
}

后台‘cs

        private void CommandBinding_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            MessageBox.Show("The New Cmd was Invoked");
        }

        private void CommandBinding_CanExecute(object sender, CanExecuteRoutedEventArgs e)
        {
            e.CanExecute = true;
        }

e.CanExecute = false;按钮就无效了

 例子1.1  使用命令参数

在此处设置参数

    <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
        <Button Command="ApplicationCommands.New" CommandParameter="NewPara" >New</Button>
    </StackPanel>

在这里获取

        private void CommandBinding_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            
            MessageBox.Show("The New Cmd was Invoked+\r\n+With Parameter ："+e.Parameter.ToString());
        }

例子2：使用CanExecute，根据业务决定按钮是否可用

    <Window.CommandBindings>
        <CommandBinding Command="ApplicationCommands.Cut" CanExecute="CutCommand_CanExecute" Executed="CutCommand_Executed" />
        <CommandBinding Command="ApplicationCommands.Paste" CanExecute="PasteCommand_CanExecute" Executed="PasteCommand_Executed" />
    </Window.CommandBindings>
    <DockPanel>
        <WrapPanel DockPanel.Dock="Top" Margin="3">
            <Button Command="ApplicationCommands.Cut" Width="60">_Cut</Button>
            <Button Command="ApplicationCommands.Paste" Width="60" Margin="3,0">_Paste</Button>
        </WrapPanel>
        <TextBox AcceptsReturn="True" Name="txtEditor" />
    </DockPanel>

        private void CutCommand_CanExecute(object sender, CanExecuteRoutedEventArgs e)
        {
            e.CanExecute = (txtEditor != null) && (txtEditor.SelectionLength > 0);
        }

        private void CutCommand_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            txtEditor.Cut();
        }

        private void PasteCommand_CanExecute(object sender, CanExecuteRoutedEventArgs e)
        {
            e.CanExecute = Clipboard.ContainsText();
        }

        private void PasteCommand_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            txtEditor.Paste();
        }

 例子3：CommandTarget

实现和例子2 相同的功能

    <DockPanel>
        <WrapPanel DockPanel.Dock="Top" Margin="3">
            <Button Command="ApplicationCommands.Cut" CommandTarget="{Binding ElementName=txtEditor}" Width="60">_Cut</Button>
            <Button Command="ApplicationCommands.Paste" CommandTarget="{Binding ElementName=txtEditor}" Width="60" Margin="3,0">_Paste</Button>
        </WrapPanel>
        <TextBox AcceptsReturn="True" Name="txtEditor" />
    </DockPanel>

 例子4：自定义Command

         xmlns:self="clr-namespace:WpfApp2"
  

 <Window.CommandBindings>
        <CommandBinding Command="self:CustomCommands.Exit" CanExecute="ExitCommand_CanExecute" Executed="ExitCommand_Executed" />
    </Window.CommandBindings>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <Menu>
            <MenuItem Header="File">
                <MenuItem Command="self:CustomCommands.Exit" />
            </MenuItem>
        </Menu>
        <StackPanel Grid.Row="1" HorizontalAlignment="Center" VerticalAlignment="Center">
            <Button Command="self:CustomCommands.Exit">Exit</Button>
        </StackPanel>
    </Grid>

后台

namespace WpfApp2
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {

        public MainWindow()
        {
            InitializeComponent();

        }
        private void ExitCommand_CanExecute(object sender, CanExecuteRoutedEventArgs e)
        {
            e.CanExecute = true;
        }

        private void ExitCommand_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            Application.Current.Shutdown();
        }

    }
    public static class CustomCommands
    {
        public static readonly RoutedUICommand Exit = new RoutedUICommand
            (
                "Exit",
                "Exit",
                typeof(CustomCommands),
                new InputGestureCollection()
                {
                    new KeyGesture(Key.F3, ModifierKeys.Alt)
                }
            );

    }
}

点击菜单，或者按钮，或者alt + F3都会关闭窗口。

 例子5 ：使用接口ICommand

接口方法的参数都是命令的参数

void Execute(object parameter);

    internal class CommandBase : ICommand
    {
        public event EventHandler CanExecuteChanged;

        public bool CanExecute(object parameter)
        {
            return DoCanExecute?.Invoke(parameter) ==true;
        }

        public void Execute(object parameter)
        {
            DoAction?.Invoke(parameter);    
        }
        public Action<object> DoAction { get; set; }
        public Func<object,bool> DoCanExecute { get;set; }
        public void RaiseCanChanged()
        {
            CanExecuteChanged?.Invoke(this,new EventArgs());
        }

    }

    public class TestViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        private ICommand _command;
        public ICommand TestCommand
        {
            get
            {
                if( _command == null )
                {
                    _command = new CommandBase()
                    {
                        DoAction = (o) => 
                        {
                            MessageBox.Show(o.ToString());
                        },
                        DoCanExecute = (o) => { return true; }

                    };
                }
                return _command;
            }

            set
            {
                _command = value;
            }
        }
    }

在窗口后台文件中

        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = new TestViewModel();
        }

    <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
        <Button Command="{Binding TestCommand}" CommandParameter="hidaf" >New</Button>
    </StackPanel>

等待

TODO

https://blog.csdn.net/hetoby/article/details/77449762

https://www.cnblogs.com/fly-bird/p/8724915.html

https://www.cnblogs.com/gaixiaojie/archive/2010/09/01/1815015.html