分页DataGrid中的CheckBox验证

[日期：2003-10-05]

来源：DotNetJunkies 作者：

[字体：大中小]

Advanced Checkbox Validation Across n-Pages for the DataGrid Control

By Oliver Degnan, Microsoft CSD, Macromedia PD

Published Date:
9/17/2002

Tested With:
ASP.NET v1

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Some time ago, the company I work for was quoting on a rewrite project from Java to .NET. One of their requirements was the ability to select up to two records from a datagrid that can then be compared to generate a PDF document on the fly.
Well, even though we did not get the job, I did come up with a nice way to do exactly what they asked for. The finished grid looks something like the one below:

This datagrid has a bunch of some very advanced features such as "Reversible Sorting", "Customized Pager", "Customized Footer", and the almighty "Checkbox Validation". This article will focus on the Checkbox Validation only.

The Setup

Private Sub DataGrid1_ItemDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.DataGridItemEventArgs) Handles DataGrid1.ItemDataBound
  '///////// Add CheckBoxes ////////////
  If (e.Item.ItemType = ListItemType.Item) Or _
      (e.Item.ItemType = ListItemType.AlternatingItem) Then
    AddCheckBox(e)
  End If
End Sub

Private Sub AddCheckBox(ByVal e As DataGridItemEventArgs)
  Dim cb As New CheckBox()
  Dim cell As TableCell = e.Item.Cells(0)
  cb.EnableViewState = True
  cb.AutoPostBack = True
  cb.ID = e.Item.ItemIndex
  cell.HorizontalAlign = HorizontalAlign.Right
  cell.Controls.Add(cb)
  'add event handler that will fire the validation
  AddHandler cb.CheckedChanged, AddressOf OnCheckedChangedEvent
End Sub

First we need to add a checkbox for every item (row) in the datagrid. This is done within the ItemDataBound event that fires for every item created. Also, make sure to add an event handler, in this case called OnCheckedChangedEvent. This event will be responsible for running the required validation subroutines. Make sure to check for the ListItemType when adding the checkbox as shown above.

Storing Selections in the View State

Private Sub OnCheckedChangedEvent(ByVal sender As Object, ByVal e As EventArgs)
  'CheckBox Event Handler
  'first delete IDs
  'then if counter WAS less than 2, add ID, else remove ID
  'then validate again to produce listbox & checkboxes

  RemoveIDFromListBox()

  If CheckBoxCount < 2 Then
    AddIDToListBox()
  Else
    RemoveIDFromListBox()
  End If
  'now check the once that have been checked previously
  ValidateCheckBoxes()

End Sub

Private Sub AddIDToListBox()

  Dim dgi As DataGridItem
  Dim chkText As String
  Dim chkValue As String
  Dim cb As CheckBox

  For Each dgi In DataGrid1.Items

    chkText = DataGrid1.Items(dgi.ItemIndex).Cells(1).Text.ToString
    chkValue = DataGrid1.Items(dgi.ItemIndex).Cells(1).Text.ToString
    cb = CType(dgi.Cells(0).Controls(0), CheckBox)

    If cb.Checked Then

      Dim litem As New ListItem()
      litem.Text = chkText.ToString
      litem.Value = chkValue.ToString

      If Not ListBox1.Items.Contains(litem) Then
        ListBox1.Items.Add(litem)
        CheckBoxCount = CheckBoxCount + 1
        If CheckBoxCount >= 2 Then
          HideRemainingCheckBoxes = True
        End If
      End If
    End If
  Next

End Sub

Private Sub RemoveIDFromListBox()

  Dim dgi As DataGridItem
  Dim chkValue As String
  Dim chkText As String
  Dim cb As CheckBox

  For Each dgi In DataGrid1.Items

    chkText = DataGrid1.Items(dgi.ItemIndex).Cells(1).Text.ToString
    chkValue = DataGrid1.Items(dgi.ItemIndex).Cells(1).Text.ToString
    cb = CType(dgi.Cells(0).Controls(0), CheckBox)

    If Not cb.Checked Then

      Dim litem As New ListItem()
      litem.Text = chkText.ToString
      litem.Value = chkValue.ToString

      If ListBox1.Items.Contains(litem) Then
        ListBox1.Items.Remove(litem)
        CheckBoxCount = CheckBoxCount - 1
        HideRemainingCheckBoxes = False
      End If
    End If
  Next

End Sub

Okay! Wow! Lot's of code. But no worries. It's half-as-much as it looks like.
The OnCheckedChangedEvent will handle the following routines:

AddIDToListBox [this is the one adding the checkbox values to the ListBox (I'll explain later)]

RemoveIDFromListBox [this one removes ALL check-marks from the checkboxes]

ValidateCheckBoxes [this is the big one and we'll get to that one later]

The AddIDToListBox routine is needed to iterate through every data grid item of the data grid for one page ONLY and retrieving the values of the checkboxes IF they are checked. If the loop finds a checked checkbox, it will create a new list item and add the item (the checkbox value) to the ListBox.

The RemoveIDFromListBox routine is needed to uncheck ALL checkboxes on the current data grid page. This is necessary for the checkbox validation to work properly, otherwise it would not be possible to de-select the last remaining checkbox since the datagrid's ItemCreated event would always re-paint the checked checkbox according to its view state.

So, what exactly is happening at the OnCheckedChangedEvent? It first un-checks all checkboxes, then, in my example, it looks at the checked checkbox count (my example only two at one time are allowed to be checked), and then determines whether we have to add the last checked checkbox, or delete the last checkbox touched (checkbox event) from the ListBox.

The ListBox is crucial to all of this. It acts as out checkbox memory. You could easily use an array, session, cache, or application object to do this. You could also change the visibility attribute for the ListBox to false and it would therefore be invisible to the end-user (IE-only). This is completely up to your preference.

Validating Checkboxes

Private Sub ValidateCheckBoxes()

  If HideRemainingCheckBoxes Then

    Dim dgi As DataGridItem
    Dim cb As CheckBox
    Dim counter As Integer
    Dim counter2 As Integer
    Dim chkValue As String

    Button1.BackColor = Color.FromName("DarkRed")
    Button1.ForeColor = Color.White
    Button1.Enabled = True

    For counter = 0 To DataGrid1.Items.Count - 1
      cb = CType(DataGrid1.Items(counter).Cells(0).Controls(0), CheckBox)
      chkValue = DataGrid1.Items(counter).Cells(1).Text.ToString
      'find match
      For counter2 = 0 To ListBox1.Items.Count
        Dim litem As New ListItem()
        litem.Text = chkValue.ToString
        litem.Value = chkValue.ToString

        If ListBox1.Items.Contains(litem) Then
          cb.Enabled = True
          cb.Checked = True
        Else
          cb.Enabled = False
          cb.Checked = False
        End If
      Next
    Next

  Else

    Dim dgi As DataGridItem
    Dim cb As CheckBox
    Dim counter As Integer
    Dim counter2 As Integer
    Dim chkValue As String

    Button1.BackColor = Color.FromName("LightGrey")
    Button1.ForeColor = Color.Black
    Button1.Enabled = False

    For counter = 0 To DataGrid1.Items.Count - 1
      cb = CType(DataGrid1.Items(counter).Cells(0).Controls(0), CheckBox)
      chkValue = DataGrid1.Items(counter).Cells(1).Text.ToString
      'find match
      For counter2 = 0 To ListBox1.Items.Count
        Dim litem As New ListItem()
        litem.Text = chkValue.ToString
        litem.Value = chkValue.ToString

        If ListBox1.Items.Contains(litem) Then
          cb.Checked = True
        Else
          cb.Enabled = True
          cb.Checked = False
        End If
      Next
    Next
  End If
  ValidateListBox()
End Sub

This is the Biggy! Basically what is happening here is that I first determine whether two checkboxes have already been checked or not. If not, I loop through every item of the data grid, get the check box value and compare it with the values stored in the listbox. If I find it in the listbox, I'll go ahead and check that one. If I didn't find a match, I'll keep it unchecked.

There is however, in my example a slight modification in case the checkbox counter value is greater or equal to two (two checkboxes have been checked already). In this case, I'll go through the same routine as described above. However, since I want only two checkboxes to be checked, I have to enable all other checkboxes EXCEPT the once matching with the values of the listbox.

And that's it. This is how you validate and remember checkboxes across the data grid.

The working example can be seen here: http://devspot.devspot.com/wise/Specs_Display_Grid

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