在 Foreach 循环 C# 中修改集合

Question

我在 foreach 循环期间更新 ObservableCollection 中的项目时遇到问题。基本上我有 ObservableCollection 名员工，他们的模型中有一个字段决定他们是否在建筑物中。

我经常查看数据库table 来检查每个员工的状态是否有任何变化。这就是我在 C#;

中的做法

public ObservableCollection<EmployeeModel> EmployeesInBuilding {get; set; }
public ObservableCollection<EmployeeModel> Employees {get; set; }

var _employeeDataService = new EmployeeDataService();
EmployeesInBuilding = _employeeDataService.GetEmployeesInBuilding();
foreach (EmployeeModel empBuild in EmployeesInBuilding)
{
    foreach (EmployeeModel emp in Employees)
    {
        if (empBuild.ID == emp.ID)
        {
            if (empBuild.InBuilding != emp.InBuilding)
            {
                emp.InBuilding = empBuild.InBuilding;
                int j = Employees.IndexOf(emp);
                Employees[j] = emp;
                employeesDataGrid.Items.Refresh();
            }
        }
    }
}

这正确地获取了两者之间的变化 ObseravbleCollections，但是当我去更新现有的 ObservableCollection 时，我得到一个异常：Collection was modified; enumeration operation may not execute.

如何防止这种情况发生并仍然修改原始集合？

Answer 1

Employees 集合中的元素只需设置属性元素就无需替换。

相反，您的 EmployeeModel class 应该实现 INotifyPropertyChanged 接口并在 InBuilding 属性更改时引发 PropertyChanged 事件：

public class EmployeeModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private bool inBuilding;
    public bool InBuilding
    {
        get { return inBuilding; }
        set
        {
            if (inBuilding != value)
            {
                inBuilding = value;
                OnPropertyChanged("InBuilding");
            }
        }
    }

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

    ...
}

现在更新代码的内部循环可以简化为：

foreach (var emp in Employees)
{
    if (empBuild.ID == emp.ID)
    {
        emp.InBuilding = empBuild.InBuilding;
    }
}

或者像这样编写整个更新循环：

foreach (var empBuild in EmployeesInBuilding)
{
    var emp = Employees.FirstOrDefault(e => e.ID == empBuild.ID);

    if (emp != null)
    {
        emp.InBuilding = empBuild.InBuilding;
    }
}

在 Foreach 循环 C# 中修改集合

Modifying a Collection in a Foreach Loop C#

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observablecollection