即使datagridview选择的单元格值返回一个字符串，combocox文本值也设置为null

Question

我正在使用async和await函数开发一个Windows窗体应用程序。我有多个依赖的组合框控件，其中c2取决于c1值，datagridview基于输入加载。当用户点击datagridview单元格时，c1文本根据选定的单元格值设置，但即使选择的单元格值返回字符串，c2文本也设置为null。请在下面找到代码片段

private void dgvAsset_SelectionChanged(object sender, EventArgs e)
    {

        DataGridViewCell cell = null; // set cell initial value to null
        foreach (DataGridViewCell selectedcell in dgvAsset.SelectedCells)
             {
                 cell = selectedcell; // load selected cell value
                 break;
             }
        if (cell != null)
        {
            DataGridViewRow sr = cell.OwningRow;
            assetID = Convert.ToInt32(sr.Cells["AssetID"].Value.ToString());
            txtAssId.Text = sr.Cells["Asset_ID"].Value.ToString();
            cbAssType.Text = sr.Cells["Asset_Type"].Value.ToString();
            txtAsSerNo.Text = sr.Cells["AssetSerialNo"].Value.ToString();
            txtAssDesc.Text = sr.Cells["Asset_Description"].Value.ToString();
            dtAFrom.Text = sr.Cells["AllocatedFrom"].Value.ToString();
            dtATo.Text = sr.Cells["AllocatedTo"].Value.ToString();
            cbProjCode.Text = sr.Cells["Project_Code"].Value.ToString();
           // this.cbProjCode.SelectionChangeCommitted -= new EventHandler(cbProjCode_SelectionChangeCommitted);
           // string port = sr.Cells["Portfolio"].Value.ToString();
           /* the below 3 combobox are set to null*/
            cbPortfolio.Text = Convert.ToString(sr.Cells["Portfolio"].FormattedValue.ToString())
            cbPOwner.Text = sr.Cells["Primary_Owner"].Value.ToString();
            cbSOwner.Text = sr.Cells["Seconday_Owner"].Value.ToString();
        }
    }

public async Task LoadProjectCode() 
{ 
    List<string> projectCode = new List<string>(); 
    projectCode = await func.LoadProjectCode(); 
// this.cbProjCode.SelectedIndexChanged -= new EventHandler(cbProjCode_SelectedIndexChanged); 
    cbProjCode.DataSource = projectCode; 
    cbProjCode.SelectedIndex = -1; 
} 




private async void cbProjCode_SelectionChangeCommitted(object sender, EventArgs e) 
{ 
    cbProjCode.Enabled = false; 
    cbAssType.Enabled = true; 
    cbPortfolio.Enabled = true; 
    cbPOwner.Enabled = true; 
    cbSOwner.Enabled = true; 
    txtAssDesc.Enabled = true; 
    txtAsSerNo.Enabled = true; 
    txtAssId.Enabled = true; ProjectCodeId = await func.GetProjectCodeID(cbProjCode.Text); 
    await LoadPortfolio(); 
} 

当我没有使用异步并且等待加载组合框并且使用了combobox selectedindexchange事件而不是之前提交的selection。时，相同的代码工作正常。