如何从DatePicker控件取值并作为参数传递给命令？

步骤1：完善ViewModel实现 #

首先需要实现ICommand的具体实现（比如RelayCommand，WPF无内置该类），同时给ViewModel添加日期属性并实现INotifyPropertyChanged接口以支持数据绑定通知：

1.1 实现RelayCommand #

public class RelayCommand : ICommand
{
    private readonly Action<object> _execute;
    private readonly Func<object, bool> _canExecute;

    public event EventHandler CanExecuteChanged;

    public RelayCommand(Action<object> execute, Func<object, bool> canExecute = null)
    {
        _execute = execute ?? throw new ArgumentNullException(nameof(execute));
        _canExecute = canExecute;
    }

    public bool CanExecute(object parameter)
    {
        return _canExecute == null || _canExecute(parameter);
    }

    public void Execute(object parameter)
    {
        _execute(parameter);
    }

    public void RaiseCanExecuteChanged()
    {
        CanExecuteChanged?.Invoke(this, EventArgs.Empty);
    }
}

1.2 修改MainWindowViewModel #

using System.ComponentModel;
using System.Windows.Input;

public class MainWindowViewModel : INotifyPropertyChanged
{
    private readonly JiraHandler jiraHandler;
    private DateTime date;

    // 绑定DatePicker的SelectedDate属性
    public DateTime Date
    {
        get => date;
        set
        {
            if (date != value)
            {
                date = value;
                OnPropertyChanged(nameof(Date));
            }
        }
    }

    public ICommand DateChosen { get; }
    public ObservableCollection<Issue> Issues { get; private set; } = new ObservableCollection<Issue>();

    public MainWindowViewModel(JiraHandler jiraHandler)
    {
        this.jiraHandler = jiraHandler;
        DateChosen = new RelayCommand(ExecuteDateChosen);
    }

    private void ExecuteDateChosen(object parameter)
    {
        // 可选择使用参数传递的日期，或ViewModel自身的Date属性
        DateTime targetDate = parameter != null ? (DateTime)parameter : Date;
        
        // 调用JiraHandler加载对应日期数据
        var loadedIssues = jiraHandler.LoadIssuesForDate(targetDate);
        
        // 更新UI绑定的集合
        Issues.Clear();
        foreach (var issue in loadedIssues)
        {
            Issues.Add(issue);
        }
    }

    // INotifyPropertyChanged接口实现
    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

步骤2：XAML绑定设置 #

有两种常见绑定方式可选：

方式一：绑定日期到ViewModel属性，命令直接调用属性值 #

适合需要在ViewModel中持久化该日期，或其他逻辑需复用的场景：

<DatePicker SelectedDate="{Binding Date, Mode=TwoWay}" />
<Button Content="加载数据" Command="{Binding DateChosen}" />

方式二：通过CommandParameter直接传递DatePicker选中值 #

无需在ViewModel中额外维护日期属性，更轻量化：

<DatePicker x:Name="TargetDatePicker" />
<Button Content="加载数据" 
        Command="{Binding DateChosen}" 
        CommandParameter="{Binding SelectedDate, ElementName=TargetDatePicker}" />

内容的提问来源于stack exchange，提问作者Atlass-