[英]Paggeable Datagrid ItemSource throws null exception
I want to create a generic Datagrid
that can paginate. 我想创建一个可以分页的通用Datagrid
。 When I call the constructor of my DataGrid_UC
and pass 20 Employees
it does stores all 20 Employees in AllObject Observable Collection
. 当我调用DataGrid_UC
的构造函数并传递20 Employees
它确实将所有20名Employees存储在AllObject Observable Collection
。 And filter out the CurrentPageItems
to be 5. But upon setting datagrid.ItemsSource = CurrentPageItems
it throws null exception
but CurrentPageItems does contain 5 items. 并将CurrentPageItems
过滤为5。但是在设置datagrid.ItemsSource = CurrentPageItems
它将throws null exception
但CurrentPageItems确实包含5个项目。
DataGrid_UC.xaml DataGrid_UC.xaml
public partial class DataGrid_UC : UserControl
{
private ObservableCollection<object> _currentPageItems;
public ObservableCollection<object> CurrentPageItems
{
get
{
return _currentPageItems;
}
private set
{
if (_currentPageItems != value)
{
_currentPageItems = value;
}
}
}
// Default Entries per page Number
private int _pageSize = 5;
public int PageSize
{
get
{
return _pageSize;
}
set
{
if (_pageSize != value)
{
_pageSize = value;
Reset();
}
}
}
public int TotalPagesNumber
{
get
{
if (AllObjects != null && PageSize > 0)
{
return (AllObjects.Count - 1) / PageSize + 1;
}
return 0;
}
}
private int _currentPageNumber = 1;
public int CurrentPageNumber
{
get
{
return _currentPageNumber;
}
protected set
{
if (_currentPageNumber != value)
{
_currentPageNumber = value;
}
}
}
protected ObservableCollection<object> AllObjects { get; set; }
public DataGrid_UC()
{
InitializeComponent();
dataGrid.ItemsSource = CurrentPageItems;
}
public DataGrid_UC(IEnumerable<object> allObjects, int? entriesPerPage = null)
{
AllObjects = new ObservableCollection<object>(allObjects);
if (entriesPerPage != null)
PageSize = (int)entriesPerPage;
SetCurrentPageItems();
}
#region Public Methods
public void GoToNextPage()
{
if (CurrentPageNumber != TotalPagesNumber)
{
CurrentPageNumber++;
SetCurrentPageItems();
}
}
public void GoToPreviousPage()
{
if (CurrentPageNumber > 1)
{
CurrentPageNumber--;
SetCurrentPageItems();
}
}
#endregion
#region Private Methods
public void SetCurrentPageItems()
{
int upperLimit = CurrentPageNumber * PageSize;
CurrentPageItems =
new ObservableCollection<object>(
AllObjects.Where(x => AllObjects.IndexOf(x) > upperLimit - (PageSize + 1) && AllObjects.IndexOf(x) < upperLimit));
dataGrid.ItemsSource = CurrentPageItems;
}
private void Reset()
{
CurrentPageNumber = 1;
SetCurrentPageItems();
}
#endregion
private void next_Click(object sender, RoutedEventArgs e)
{
if (CurrentPageNumber != TotalPagesNumber)
{
CurrentPageNumber++;
SetCurrentPageItems();
}
}
private void previous_Click(object sender, RoutedEventArgs e)
{
if (CurrentPageNumber > 1)
{
CurrentPageNumber--;
SetCurrentPageItems();
}
}
}
Main Window.xaml 主窗口.xaml
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
List<Employee> emp = new List<Employee>();
for (int i = 0; i < 20; i++)
{
Employee e = new Employee();
e.ID = i;
e.Name = "Test " + i;
emp.Add(e);
}
DataGrid_UC d = new DataGrid_UC(emp, 5);
newContentControl.Content = d;
}
}
The dataGrid
member is null because your second constructor is missing the InitializeComponent
call, which (among other things) initializes the class members defined in XAML by x:Name
. dataGrid
成员为null,因为您的第二个构造函数缺少InitializeComponent
调用,该调用(除其他外)初始化xAML中通过x:Name
定义的类成员。
So change the constructor like this: 因此,像这样更改构造函数:
public DataGrid_UC(IEnumerable<object> allObjects, int? entriesPerPage = null)
{
InitializeComponent();
AllObjects = new ObservableCollection<object>(allObjects);
...
}
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