Question

我有一些代码，单击一下按钮即可创建几个组合框。像这样的东西。

for (int i =0; i< noCol;i++){
tableLayoutPanel2.RowCount = tableLayoutPanel2.RowCount + 1;
tableLayoutPanel2.Controls.Add(new Label() { Text = "العمود " + (i+1) }, 0, (i));
var com = new ComboBox();
com.Name = "reportColumn" + (i + 1).ToString();
g = tableLayoutPanel2.Controls[com.Name] as ComboBox;
c.Add(g);
g.SelectedIndexChanged += new EventHandler(ReportWizardStep1ComboboxSelectedIndexchanged);
tableLayoutPanel2.Controls.Add(com,1,i);}

private void ReportWizardStep1ComboboxSelectedIndexchanged(object sender, EventArgs e){ComboBox combo = sender as ComboBox;
MainForm.exportReport.getDataGridView1().ColumnCount++;
MainForm.exportReport.getDataGridView1().Columns
            [MainForm.exportReport.getDataGridView1().ColumnCount - 1].HeaderText = g.Text;
comboValues.Add(g.Text);}

但是，当我运行代码时，此行抛出异常：

g.SelectedIndexChanged += new EventHandler(ReportWizardStep1ComboboxSelectedIndexchanged);
tableLayoutPanel2.Controls.Add(com,1,i);

例外是：

发生类型'System.NullReferenceException'的异常。我该如何解决这个问题

Answer 1

Sub ColorSheetFive()
    Dim i As Integer
    Dim m As Integer
    Dim n As Integer
    Dim allGreen As Boolean

    For m = 2 To 26
        For n = 2 To 62
            allGreen = True
            For i = 1 To 4
                If Sheets(i).Cells(m, n).Interior.Color <> RGB(0, 255, 0) Then
                    allGreen = False
                End If
            Next i
            If allGreen Then
                Sheets(5).Cells(m, n).Interior.Color = RGB(0, 255, 0)
            End If
        Next n
    Next m

    MsgBox "Color checking complete!"

End Sub

您正在创建一个新的组合框，设置一个名称，然后在tableLayoutPanel2.Controls中搜索此新创建的控件。该控件可能会返回null ...您应该在查找它之前先添加它。

如何引用动态创建的组合框？

1 个答案: