Question

我是Stack Overflow的新手，所以请原谅任何不正确的表格/礼节。谢谢！

编辑：我想我的问题不是关于如何修复NullReference异常，而是如何正确处理它＆＃34;退出＆＃34;当我点击它之外的组合框。

我正在使用我正在使用的DataGridViewComboBoxCell设置。首先，我有一个包含3列的datagridview，在用户启用编辑后，使用DataGridViewComboBoxCell填充单元格。在每一行中，这3个单元格依赖于前一个单元格中的选定项目（第一个ComboBoxCell除外）。我遇到的问题是，如果我点击第一个ComboBox，我让它显示下拉列表，但我实际上没有选择任何东西，我移动到下一个ComboBoxCell并尝试单击它以查看其项目列表它会停止程序并为＆＃34生成错误; NullReference异常未处理＆＃34;。此异常出现在＆＃34; static void Main（）＆＃34;在Application.Run（new MainForm（））;

处理更改ComboBox所选索引的代码，该索引应自动填充其他ComboBox。

private void LoadRules_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
    {

        DataGridViewComboBoxEditingControl cbx = e.Control as DataGridViewComboBoxEditingControl;
        if (cbx != null)
        {

            if (this.LoadRulesDataGridView.Columns[LoadRulesDataGridView.CurrentCell.ColumnIndex].Name.Equals("OEM"))
            {
                ComboBox cmbprocess = e.Control as ComboBox;


                cmbprocess.SelectedIndexChanged += new EventHandler(OEMBox_SelectedIndexChanged);
                cmbprocess.SelectedIndexChanged += new EventHandler(ModelBox_SelectedIndexChanged);
            }
        }

    }

    private void OEMBox_SelectedIndexChanged(object sender, EventArgs e)
    {
        NetMonDB.DBManager dbConn = new NetMonDB.DBManager(ConnStr, this.LogWarning, this.LogError);
        ComboBox cmbprocess = (ComboBox)sender;

        int row = this.LoadRulesDataGridView.CurrentCell.RowIndex;
        string OEM = cmbprocess.SelectedItem.ToString();
        this.RulesGridModels(row, cmbprocess, dbConn, OEM);//this method gets the required info from the database and loads it into the ComboBox

        cmbprocess.SelectedIndexChanged -= new EventHandler(OEMBox_SelectedIndexChanged);
    }

    private void ModelBox_SelectedIndexChanged(object sender, EventArgs e)
    {
        NetMonDB.DBManager dbConn = new NetMonDB.DBManager(ConnStr, this.LogWarning, this.LogError);
        ComboBox cmbprocess = (ComboBox)sender;

        int row = this.LoadRulesDataGridView.CurrentCell.RowIndex;
        string Model = cmbprocess.SelectedItem.ToString();
        string OEM = cmbprocess.SelectedItem.ToString();
        this.RulesGridOSVersions(row, cmbprocess, dbConn, OEM, Model);//this method gets the required info from the database and loads it into the ComboBox

        cmbprocess.SelectedIndexChanged -= new EventHandler(ModelBox_SelectedIndexChanged);
    }

更新ComboBox的方法。

private void RulesGridModels(int r, ComboBox comboBox, NetMonDB.DBManager dbConn, string rowOEM)
    {
        //MessageBox.Show(this.LoadRulesDataGridView.Rows[0].Cells[4].Value.ToString());
        DataGridViewComboBoxCell cbo = new DataGridViewComboBoxCell();

        for (int i = 0; i < comboBox.Items.Count; i++)
        {
            cbo.Items.AddRange(comboBox.Items[i]);
        }
        try
        {
            cbo.Items.Clear();
            cbo.Items.AddRange("");
            if (this.LoadRulesDataGridView.Rows[r].Cells[4].Value == null)
                this.LoadRulesDataGridView.Rows[r].Cells[4].Value = "";

            NetMonDB.Phone OEMPhone = dbConn.getOEMId(rowOEM);
            foreach (NetMonDB.Phone phone in dbConn.getModel(OEMPhone))
            {
                cbo.Items.Add(phone.Model);
            }
            this.LoadRulesDataGridView.Rows[r].Cells[5] = cbo;
        }
        catch (Exception e)
        {
            LogError("RulesGridModels", e.ToString());
        }
    }

    private void RulesGridOSVersions(int r, ComboBox comboBox, NetMonDB.DBManager dbConn, string rowOEM, string rowModel)
    {
        DataGridViewComboBoxCell cbo = new DataGridViewComboBoxCell();

        for (int i = 0; i < comboBox.Items.Count; i++)
        {
            cbo.Items.AddRange(comboBox.Items[i]);
        }
        try
        {

            cbo.Items.Clear();
            cbo.Items.AddRange("");
            NetMonDB.Phone CurrentPhone = dbConn.getOEMId(rowOEM);
            CurrentPhone.Model = rowModel;
            foreach (NetMonDB.Phone phone in dbConn.getOSVersion(CurrentPhone))
            {
                cbo.Items.Add(phone.OSVersion);
            }
            this.LoadRulesDataGridView.Rows[r].Cells[6] = cbo;
        }
        catch (Exception e)
        {
            LogError("RulesGridOSVersions", e.ToString());
        }

    }

发现异常的地方。

static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new MainForm());//Crashes at this Point
    }

Answer 1

在这样的情况下我遇到了同样的问题，我发现作为此问题的解决方案的是使用 SelectionChangeCommitted代替SelectedIndexChanged事件进行组合。< / p>

DataGridViewComboBoxCell创建Null引用异常

1 个答案: