VB.NET 中未处理 InvalidCastException

Question

参考这个问题：StackOverflowException was unhandled in VB.NET 我决定创建一个新问题，因为我有一个新错误。

无法将“System.Windows.Forms.BindingSource”类型的对象转换为“System.Data.DataTable”类型。

代码（在按钮点击事件中）：

' Copy rows from the first datagridview to the second datagridview that is data bound
    ' First copy the second datagridviews datasource into a new data table

    Dim dt As DataTable = CType(frmEncodeDatabase.EncodingDataGridView.DataSource, DataTable).Copy
    Dim dr As DataRow

    ' Loop through all rows of the first datagridview and copy them into the data table

    For r As Int32 = 0 To Me.DataGridViewX1.Rows.Count - 1
        If Me.DataGridViewX1.Rows(r).IsNewRow = False Then   ' Do not copy the new row
            dr = dt.NewRow

            ' Loop through all cells of the first datagridview and populate the data row

            For c As Int32 = 0 To Me.DataGridViewX1.ColumnCount - 1
                dr(c) = Me.DataGridViewX1.Rows(r).Cells(c).Value
            Next

            dt.Rows.Add(dr) ' Add the data row to the data table
        End If
    Next

    Me.DataGridView2.DataSource = dt    ' Rebind the second datagridview with the new table which has all the rows from both datagridviews
    frmEncodeDatabase.show()

图像中的错误在dt As DataTable = CType(frmEncodeDatabase.EncodingDataGridView.DataSource, DataTable).Copy 中，错误现在就在其中。我将如何修改代码？

Answer 1

错误消息是不言自明的。

“无法将 'BindingSource' 类型的对象转换为 'DataTable' 类型。”

你的datagridview的数据源是BindingSource，所以你需要转换成这个类型。

Dim bs As BindingSource = CType(frmEncodeDatabase.EncodingDataGridView.DataSource, BindingSource)

假设bindingsource的数据源是一个数据表：

Dim dt As DataTable = CType(bs.DataSource, DataTable)

如果没有，你会得到另一个强制转换异常，但现在你如何解决它。