遍历ObservableCollection<T> 值[重复]

Question

这个问题在这里已经有了答案:

什么是NullReferenceException，如何解决？ (28个回答)

封闭 上月.

我试图在WPF中创建一个库，用于从可观察的集合中创建报表，但我不知道如何循环使用。ObservableCollection 将数值写入 FlowDocument 表。我试着把通用集合投到一个 IEnumerable但是，我一直得到

抛出异常：'System.NullReferenceException'。

目标是写一个库，它将接受所有的 ObservableCollection 类型，所以我写了这个类（片段）。

public class Report_Definition<T> : INotifyPropertyChanged
{
        public Report_Definition(FlowDocument doc, ObservableCollection<T> data)
        {
            Fill_data(data, doc);
        }

        private void Fill_data(ObservableCollection<T> data, FlowDocument doc)
        {
            //I only take 25 records from ObservableCollection - to create more Tables
            for (int i = 0; i < data.Count; i += 25)
            {
                var list = (from c in data select c).Skip(i).Take(25);

                 if (i < 25) //Test for only first Table
                {
                    for (int row = 0; row < list.Count(); row++)
                    {
                        TableRow my_cell = new TableRow();

                        foreach (var item in list)
                        {
                            foreach (var w in item as IEnumerable<T>) //ERROR HERE !!!
                            {
                                my_cell.Cells.Add(new TableCell(new Paragraph(new Run(w.ToString()))) { Padding = new Thickness(2), BorderBrush = Brushes.Black, BorderThickness = new Thickness(0.7) });
                            }

                        }

                        TableRowGroup whole_row = new TableRowGroup();
                        whole_row.Rows.Add(my_cell);
                        My_table.RowGroups.Add(whole_row); //I get reference of this elsewhere...
                    }
                }
        }
}

这是我的 Employee 类。

public class Employee : INotifyPropertyChanged
{
        public string Name { get; set; }
        public string Surname { get; set; }
        public string Address { get; set; }
        public string Country { get; set; }

        #region INotifyPropertyChanged

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

        #endregion
}

所以我用大写的 ObservableCollection(Employee)而我想遍历每一个 Employee 在这个集合中写值到表格行中。

目前这段代码只将类型写入单元格中，例如：. My_Project.Model.Employee.

谁能告诉我如何正确地做到这一点？

P.S.: 正如你所看到的，我遵循的是MVVM方法。

Answer 1

假设这是一个类，你有

public class Employee
{
    public string Name { get; set; }
    public string Surname { get; set; }
    public string Address { get; set; }
    public string Country { get; set; }
}

以下代码将产生以下输出

    var props = typeof(Employee).GetProperties();

    var employee = new Employee { Name = "Athul", Surname = "Raj", Address = "Blah", Country = "India" };

    foreach (var prop in props)
    {
        Console.WriteLine($"{prop.Name} = {prop.GetValue(employee)}");
    }

    Console.ReadKey();

.

Name = Athul
Surname = Raj
Address = Blah
Country = India

你可以在方法中使用typeof(T).GetProperties()代替typeof(Employee).GetProperties()。

Answer 2

对于获取属性和为新单元格添加值，类似这样的东西可能会有用。

var props = item.GetType().GetProperties(BindingFlags.Public | BindingFlags.Instance);
foreach (var p in props) 
{
    my_cell.Cells.Add(new TableCell(new Paragraph(new Run(p.GetValue(this).ToString()))) { Padding = new Thickness(2), BorderBrush = Brushes.Black, BorderThickness = new Thickness(0.7) });
}