vb.net 获取VB.Net中ListView特定列中所有值的总和
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Get the sum of all values in a specific column of a ListView in VB.Net
提问by Chip Datamaker
I am trying to get the sum of all the current values in column 2 of a "ListView". I keep getting a "null value" exception for :
我正在尝试获取“ListView”第 2 列中所有当前值的总和。我不断收到“空值”异常：
Me.ListView1.GetItemAt(ListView1.FocusedItem.Index, 2).Text)
and I also tried this which still threw the exception:
我也试过这个仍然抛出异常：
Dim X As Double = CDbl(Form1.ListView1.Items.Item(Index).SubItems(2).Text)
The Code block that is giving me the exception is:
给我例外的代码块是：
Public Sub getSubtotal()
Dim Index As Integer
Dim TotalValue As Double
For Index = 1 To Form1.ListView1.Items.Count - 1
Dim X As Double = CDbl(Form1.ListView1.Items.Item(Index).SubItems(2).Text)
TotalValue = TotalValue + X
Next
MsgBox(TotalValue)
采纳答案by ??ssa P?ngj?rdenlarp
A thing to keep in mind with the ListView, is that SubItem(0)refers to the ListViewItem, so SubItem(1)will reference the first actual subitem. So your index of 2 is actually referring to what appears in the third "column".
需要记住的ListView, 是SubItem(0)指ListViewItem，因此SubItem(1)将引用第一个实际子项。所以你的索引 2 实际上是指第三个“列”中出现的内容。
You define TotalValueinside a Sub which makes it a local variable - it only resides there. Assuming the Total is of some interest, the procedure should be a Function returning that value. Also, your loop skips the first item, is a little wordy, and the existence of Form1.indicates you are not using explicit form references (use Meto reference the current form instance):
您TotalValue在 Sub 内部定义，使其成为局部变量 - 它仅驻留在那里。假设对 Total 感兴趣，该过程应该是一个返回该值的函数。此外，您的循环跳过第一项，有点冗长，存在Form1.表明您没有使用显式表单引用（用于Me引用当前表单实例）：
' Optional ToDo: pass a int value indicating which "column" to add up
Public Function GetSubTotal() As Decimal
Dim TotalValue As Decimal
Dim tmp As Decimal
' arrays and collections start at index(0) not (1)
' OP code would skip the first item
For n as Integer = 0 To ListView1.Items.Count - 1
' ToDo: Not all items must have the same number of SubItems
' should also check SubItems Count >= 1 for each item
' try to get the value:
If Decimal.TryParse(ListView1.Items(n).SubItems(1).Text, tmp) Then
TotalValue += tmp
End If
Next
Return TotalValue
End Function
回答by Waruna Manjula
Dim Index As Integer
Dim TotalValue As Double
For Index = 1 To ListView1.ListItems.Count
TotalValue = TotalValue + ListView1.ListItems(Index).SubItems(2)
Next
MsgBox(TotalValue)
