Question

当我在datagridview中使用selectionchanged事件时。如果我点击列标题，它会给我异常： NullReferenceException未被用户代码处理对象引用未设置为对象的实例。

这是我的代码

    private void dgvEvents_SelectionChanged(object sender, EventArgs e)
    {
        //
        //Select By EventID Operation.
        //
        eventID = int.Parse(dgvEvents.Rows[dgvEvents.CurrentRow.Index].Cells["EventID"].Value.ToString());
        EventEntity = EventsMethods.SelectByID(eventID);
        txtEventName.Text = EventEntity.Name;
        cboxEventsCategories.SelectedValue = EventEntity.EventCategoryID;
        dateTimePickerEvent.Text = EventEntity.Date.ToString();
        txtBenefNum.Text = EventEntity.BeneficiariesNumber.ToString();
        txtResultB.Text = EventEntity.ResultBefore.ToString();
        txtResultA.Text = EventEntity.ResultAfter.ToString();
        txtPercentage.Text = EventEntity.Percentage.ToString();
        //
        //Show EventsMembers.
        //
        FillEventsMembersDGV();
    }

Answer 1

您可能会收到此错误，因为当它不是有效选择（即-1）时会触发事件，从而抛出此异常。试试这个：

   if ((e.RowIndex >= 0) && (e.ColumnIndex >= 0))
    {
            //
            //Select By EventID Operation.
            //

            //Also, use Convert.ToString() rather than .ToString();
            eventID = int.Parse(Convert.ToString(dgvEvents.Rows[dgvEvents.CurrentRow.Index].Cells["EventID"].Value));
            EventEntity = EventsMethods.SelectByID(eventID);
            txtEventName.Text = EventEntity.Name;
            cboxEventsCategories.SelectedValue = EventEntity.EventCategoryID;
            dateTimePickerEvent.Text = EventEntity.Date.ToString();
            txtBenefNum.Text = EventEntity.BeneficiariesNumber.ToString();
            txtResultB.Text = EventEntity.ResultBefore.ToString();
            txtResultA.Text = EventEntity.ResultAfter.ToString();
            txtPercentage.Text = EventEntity.Percentage.ToString();
            //
            //Show EventsMembers.
            //
            FillEventsMembersDGV();
    }

Answer 2

其中一个是返回一个空对象......

dgvEvents.Rows[dgvEvents.CurrentRow.Index].Cells["EventID"].Value.ToSt‌ring()

可以是以下任何一种：

dgvEvents
dgvEvents.CurrentRow
dgvEvents.Rows[....]
dgvEvents.Rows[....].Cells
dgvEvents.Rows[....].Cells["EventID"]
dgvEvents.Rows[....].Cells["EventID"].Value

最好的方法是将其分解为步骤：

    var curRow= dvgEvents.CurrentRow;
    if ( curRow != null )
         var index = curRow.Index;

// etc

C＃datagridview selectionchanged事件错误

2 个答案: