List和ObservableCollection和ListBinding在MVVM模式下的对比

List

当对List进行增删操作后，并不会对View进行通知。

csharp 复制代码

//Employee
public class Employee : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler? PropertyChanged;
    public string Name { get; set; }
    private int salary;
    public int Salary
    {
        get { return salary; }
        set
        {
            salary = value;
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Salary)));
        }
    }
}

xml 复制代码

<!--View-->
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition />
        <RowDefinition Height="40" />
    </Grid.RowDefinitions>
    <DataGrid ItemsSource="{Binding Employees}" />
    <StackPanel
        Grid.Row="1"
        VerticalAlignment="Center"
        Orientation="Horizontal">
        <Button Command="{Binding addCommand}" Content="Add" />
        <TextBlock Text="工资总额" />
        <TextBox Text="{Binding TotalSalary, Mode=OneWay}" />
    </StackPanel>
</Grid>

csharp 复制代码

//MainViewModel
public partial class MainViewModel:INotifyPropertyChanged
{
    public List<Employee> Employees { get; }
    public int TotalSalary=>Employees.Sum(x => x.Salary);

    
    public MainViewModel()
    {
        Employees = new List<Employee>() { 
            new Employee(){Name="Tom",Salary=200},
            new Employee(){Name="Tim",Salary=450},
            new Employee(){Name="Jerry",Salary=780},
            new Employee(){Name="Jake",Salary=540},
            new Employee(){Name="Kit",Salary=670},
        };
        
    }
    [RelayCommand]
    private void add()
    {
        Employees.Add(new Employee() {  Name = "Lit", Salary = 260 });
        //通知TotalSalay
        PropertyChanged?.Invoke(this,new PropertyChangedEventArgs(nameof(TotalSalary)));
    }

    public event PropertyChangedEventHandler? PropertyChanged;
}

可以看到，点击Add后，上面列表中并没有更新，但是工资总额已经更新，这说明新的数据已经加到了List中，但是List并没有通知View。

ObservableCollection

ObservableCollection可以在增加和删除时，对View进行通知

修改MainViewModel

csharp 复制代码

public partial class MainViewModel:INotifyPropertyChanged
{
    public ObservableCollection<Employee> Employees { get; }
    public int TotalSalary=>Employees.Sum(x => x.Salary);

    
    public MainViewModel()
    {
        Employees = new ObservableCollection<Employee>() { 
            new Employee(){Name="Tom",Salary=200},
            new Employee(){Name="Tim",Salary=450},
            new Employee(){Name="Jerry",Salary=780},
            new Employee(){Name="Jake",Salary=540},
            new Employee(){Name="Kit",Salary=670},
        };
        
    }
    [RelayCommand]
    private void add()
    {
        Employees.Add(new Employee() {  Name = "Lit", Salary = 260 });
        PropertyChanged?.Invoke(this,new PropertyChangedEventArgs(nameof(TotalSalary)));
    }
    //增加一个Modify方法
    [RelayCommand]
    private void Modify()
    {
        Employees[2].Salary = 999;
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(TotalSalary)));
    }

    public event PropertyChangedEventHandler? PropertyChanged;
}

可以发现，点击Add，View中也相应地进行了更新，而且工资总额也相应改变。同时，无论是add还是Modify，都使用了PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(TotalSalary)));它的改进做法是使用CollectionChanged事件。

csharp 复制代码

//改进做法,增加CollectionChanged，可以删除add()和Modify()的PropertyChanged...了
Employees.CollectionChanged += (_, _) => { PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(TotalSalary))); };

BindingList

BindingList提供了更多的功能，提供了排序、搜索、过滤等功能。此外，BindingList 还提供了对数据源的更多控制，如 AllowNew、AllowEdit 和 AllowRemove 属性，用于控制是否允许添加、编辑和删除项。

BindingList提供了ListChanged事件，该事件参数中提供了详细的信息，但是ObservableCollection 是线程安全的，可以在多个线程中使用。而 BindingList 不是线程安全的，如果需要在多个线程中使用，需要进行额外的线程同步处理。