Question

我正在调查如何在循环内部修改循环结束值。这是.NET2代码（我正在使用VB）。我明白这不太理想，但可以做到吗？

'inital value is 31
Dim currentNumberOfRowsInDataTable As Int32 = dataTable.Rows.Count - 1

For i As Integer = 0 To currentNumberOfRowsInDataTable
    Try
        If (dataTable.Rows(i)("DataItemSection") = "Platforms") Then
            Dim newRow As DataRow = rearrangedDataTable.NewRow()

            'do stuff

            dataTable.Rows.RemoveAt(i)
            'decrement to 30, however this has no influence on the loop
            currentNumberOfRowsInDataTable -= 1
        End If
    Catch
        'problem is that loop always goes to 31, whereas I want it to go to 30
        'so need to swallow the exception here
    End Try
Next

编辑 - 这里有C＃代码，但是因为它没有产生相同的行为而把它拿出来。

Answer 1

如果您在循环浏览时从列表中删除某些内容，则应该从最后开始。 C＃：

for (int i = currentNumberOfRowsInDataTable - 1; i >= 0; --i) {
  //the rest here
}

引用：

//decrement to 30, however this has no influence on the loop
currentNumberOfRowsInDataTable -= 1;

结束语

这将影响循环。但是，如果你从最后开始，整个问题就会消失。

Answer 2

我认为使用while loop符合您的要求

VB代码：

'inital value is 31
Dim currentNumberOfRowsInDataTable As Int32 = dataTable.Rows.Count - 1
Dim i As Integer = 0

While i <= currentNumberOfRowsInDataTable 
    Try
        If (dataTable.Rows(i)("DataItemSection") = "Platforms") Then
            Dim newRow As DataRow = rearrangedDataTable.NewRow()

            'do stuff

            dataTable.Rows.RemoveAt(i)
            'decrement to 30, however this has no influence on the loop
            currentNumberOfRowsInDataTable -= 1
        Else  
            i += 1
        End If
    Catch
        'problem is that loop always goes to 31, whereas I want it to go to 30
        'so need to swallow the exception here
    End Try
End While

修改我删除了C＃代码，因为你使用的是VB.NET，看起来你不需要进行C＃转换。正如@Damien_The_Unbeliever所说，如果我们删除i处的行，那么下一行将取代已删除的行，因此我前面的代码将导致在{{的当前行时缺少对下一行的检查1}}被删除。为了避免这种情况，请将i的增量放入i块，这样else只会在没有删除行的情况下增加。我更新了上面的代码

.NET更改内循环时循环的次数

2 个答案: