ComboBox 不接受所选项目的 Null [关闭]

Question

我收到以下异常：

System.FormatException: 输入字符串格式不正确

我收到此异常消息是因为我有一个 Selection Change Event 填充 Comboboxes 和 TextBoxes 中的数据来自 DataGrid 中的选定行

我的ComboBox 显示从DataGrid 行中选择的项目，当单击下拉列表时，它会显示剩余的Selected Item List

如果从DataGrid 中选择的行是NULL，那么我会收到此异常消息，因为我的ComboBox 无法将Null 识别为其列表中的项目之一。

这是我的Selection Change Event 代码，我在cmb_DisputeClassification.SelectedValue = row_selected["FR_DSP_CLSF"].ToString(); 线上遇到了这个异常

        private void dtGrid_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {

        // When a respective row is selected
        // Populate the key dispute information in botton left panel. 
        DataGrid gd = (DataGrid)sender;
        DataRowView row_selected = gd.SelectedItem as DataRowView;

        if (row_selected != null)
        {
            // Customer Information Menu
            txt_acct.Text = row_selected["ACCOUNT"].ToString();
            txt_custname.Text = row_selected["CUST_NAME"].ToString();
            txt_address.Text = row_selected["PREM_ADDR"].ToString();
            txt_revclass.Text = row_selected["RateType"].ToString();
            txt_DisplayID.Text = row_selected["DSP_ID"].ToString();



            // Dispute Information Menu - Review Section

            // Review Notes Textbox
            txt_ReviewNotes.Text = row_selected["FR_CMMNT"].ToString();
            txt_ResolutionNotes.Text = row_selected["COMMENT"].ToString();
            DatePicker_ScheduledFor.Text = row_selected["FR_SO_DT_WNTD"].ToString();
            txt_WFMissuedBy.Text = row_selected["NM_USER"].ToString();


            // First Review Parse is needed for ShortDate format.
            if (row_selected["FR_DT_FIRSTREV"] != null)
            {
                DateTime dateTime;
                if (DateTime.TryParse(row_selected["FR_DT_FIRSTREV"].ToString(), out dateTime))
                {
                    txt_firstreview.Text = dateTime.ToShortDateString();
                }
                else
                {
                    txt_firstreview.Text = ""; //assign default value
                }
            }

            // First Review Parse is needed for ShortDate format.
            if (row_selected["FR_TS_LATESTUPD"] != null)
            {
                DateTime dateTime;
                if (DateTime.TryParse(row_selected["FR_TS_LATESTUPD"].ToString(), out dateTime))
                {
                    txt_Latestupdate.Text = dateTime.ToShortDateString();
                }
                else
                {
                    txt_Latestupdate.Text = ""; //assign default value
                }
            }

            // Comboboxes 

            SqlConnection connection = new SqlConnection("Data Source=WINDOWS-B1AT5HC\\SQLEXPRESS;Initial Catalog=CustomerRelations;Integrated Security=True;");

            try
            {
                // Dispute Classification ComboBox
                SqlDataAdapter Status_data0 = new SqlDataAdapter("SELECT * FROM [hb_DspClsf]", connection);
                DataSet ds0 = new DataSet();
                Status_data0.Fill(ds0, "t");

                cmb_DisputeClassification.ItemsSource = ds0.Tables["t"].DefaultView;
                cmb_DisputeClassification.DisplayMemberPath = "TXT_DSP_CLSF";
                cmb_DisputeClassification.SelectedValuePath = "KY_DSP_CLSF";
                cmb_DisputeClassification.SelectedValue = row_selected["FR_DSP_CLSF"].ToString();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }

        }
    }

Answer 1

错误不是由 Combobox 引起的，而是由同一行上的 ToString() 调用引起的，您不能在 NULL 引用上调用。

string myString = null
myString; //no error
myString.ToString(); //error

但是，使用Convert.ToString() 可以避免这个问题。

string myString = null
Convert.ToString(myString) //no error