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。
//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)));
}
}
}
<!--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>
//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
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。
//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。文章来源:https://www.toymoban.com/news/detail-661206.html
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。文章来源地址https://www.toymoban.com/news/detail-661206.html
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