public event EventHandler ChartDataChanged; protected virtual void OnChartDataChanged() { if (ChartDataChanged != null) { ChartDataChanged(this, EventArgs.Empty); } }解释

这段代码是一个标准的 C# 事件实现。首先，代码定义了一个名为 ChartDataChanged 的事件，它的类型是 EventHandler。这意味着当事件被触发时，它会向所有已注册的处理程序发送一个 EventArgs 参数。然后，在方法 OnChartDataChanged() 中，代码检查 ChartDataChanged 是否为 null，如果不是，则调用 ChartDataChanged 事件，并传递 this 和 EventArgs.Empty 作为参数。这样，所有已注册的处理程序都会收到事件通知，并执行它们的逻辑以响应事件。

相关问题

请帮我写一份winform的自定义Silder控件用来进行视频进度条显示

好的，以下是一个简单的winform自定义Slider控件的代码示例：

using System;
using System.Drawing;
using System.Windows.Forms;

public class CustomSlider : Control
{
    private int _minimum = 0;
    private int _maximum = 100;
    private int _value = 0;

    public int Minimum
    {
        get { return _minimum; }
        set
        {
            _minimum = value;
            if (_minimum > _maximum)
                _maximum = _minimum;
            if (_value < _minimum)
                _value = _minimum;
            Invalidate();
        }
    }

    public int Maximum
    {
        get { return _maximum; }
        set
        {
            _maximum = value;
            if (_maximum < _minimum)
                _minimum = _maximum;
            if (_value > _maximum)
                _value = _maximum;
            Invalidate();
        }
    }

    public int Value
    {
        get { return _value; }
        set
        {
            if (_value != value)
            {
                if (value < _minimum)
                    _value = _minimum;
                else if (value > _maximum)
                    _value = _maximum;
                else
                    _value = value;
                Invalidate();
                OnValueChanged(EventArgs.Empty);
            }
        }
    }

    public event EventHandler ValueChanged;

    protected virtual void OnValueChanged(EventArgs e)
    {
        if (ValueChanged != null)
            ValueChanged(this, e);
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);

        // 绘制背景
        e.Graphics.Clear(BackColor);

        // 绘制进度条
        int barWidth = (int)((Width - 6) * ((double)(_value - _minimum) / (_maximum - _minimum)));
        Rectangle barRect = new Rectangle(3, (Height - 8) / 2, barWidth, 8);
        e.Graphics.FillRectangle(Brushes.Blue, barRect);

        // 绘制边框
        e.Graphics.DrawRectangle(Pens.Black, 0, 0, Width - 1, Height - 1);
    }

    protected override void OnMouseDown(MouseEventArgs e)
    {
        base.OnMouseDown(e);

        // 根据鼠标位置计算新的值
        int newValue = _minimum + (int)((double)(e.X - 3) / (Width - 6) * (_maximum - _minimum));
        Value = newValue;
    }
}

这个控件可以通过设置Minimum、Maximum和Value属性来控制进度条的显示，也可以通过订阅ValueChanged事件来响应值的变化。在OnPaint方法中，我们使用Graphics对象绘制了一个蓝色的进度条和一个黑色的边框。在OnMouseDown方法中，我们根据鼠标位置计算新的值，并调用Value属性来设置它。

WPF 使用MVVM的增删改查例子

以下是一个简单的使用MVVM实现增删改查的WPF例子：

Model类：

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
}

ViewModel类：

public class PersonViewModel : INotifyPropertyChanged
{
    private ObservableCollection<Person> _people;

    public ObservableCollection<Person> People
    {
        get { return _people; }
        set
        {
            if (_people != value)
            {
                _people = value;
                OnPropertyChanged("People");
            }
        }
    }

    private Person _selectedPerson;

    public Person SelectedPerson
    {
        get { return _selectedPerson; }
        set
        {
            if (_selectedPerson != value)
            {
                _selectedPerson = value;
                OnPropertyChanged("SelectedPerson");
            }
        }
    }

    public ICommand AddCommand { get; set; }
    public ICommand UpdateCommand { get; set; }
    public ICommand DeleteCommand { get; set; }

    public PersonViewModel()
    {
        // 初始化数据
        People = new ObservableCollection<Person>
        {
            new Person { Id=1, Name="Tom", Age=20 },
            new Person { Id=2, Name="Jerry", Age=30 },
        };

        // 添加命令
        AddCommand = new RelayCommand(AddPerson);
        // 修改命令
        UpdateCommand = new RelayCommand(UpdatePerson, CanUpdatePerson);
        // 删除命令
        DeleteCommand = new RelayCommand(DeletePerson, CanDeletePerson);
    }

    private void AddPerson()
    {
        // 创建新实例
        var person = new Person();
        // 将新实例添加到列表中
        People.Add(person);
        // 设置选中项为新实例
        SelectedPerson = person;
    }

    private void UpdatePerson()
    {
        // 更新选中项
        SelectedPerson.Name = "New Name";
        SelectedPerson.Age = 25;
    }

    private bool CanUpdatePerson()
    {
        // 如果没有选中项，则不能修改
        return SelectedPerson != null;
    }

    private void DeletePerson()
    {
        // 删除选中项
        People.Remove(SelectedPerson);
        // 清空选中项
        SelectedPerson = null;
    }

    private bool CanDeletePerson()
    {
        // 如果没有选中项，则不能删除
        return SelectedPerson != null;
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

View：

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525"
        DataContext="{StaticResource PersonViewModel}">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <StackPanel Grid.Row="0" Orientation="Horizontal">
            <Button Content="Add" Command="{Binding AddCommand}"/>
            <Button Content="Update" Command="{Binding UpdateCommand}"/>
            <Button Content="Delete" Command="{Binding DeleteCommand}"/>
        </StackPanel>
        <ListBox Grid.Row="1" ItemsSource="{Binding People}"
                 SelectedItem="{Binding SelectedPerson}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel>
                        <TextBlock Text="{Binding Name}"/>
                        <TextBlock Text="{Binding Age}"/>
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</Window>

在View中设置DataContext为ViewModel实例，并绑定AddCommand、UpdateCommand和DeleteCommand到Button的Command属性上，绑定People到ListBox的ItemsSource属性上，绑定SelectedPerson到ListBox的SelectedItem属性上。

使用RelayCommand类实现命令，该类可以在WPF中重复使用，代码如下：

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

    public RelayCommand(Action execute)
        : this(execute, null)
    {
    }

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

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

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

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