Question

我正在尝试从组合框中获取当前选择的选项，我尝试通过

获取文本

ComboBox.Text

Combobox.SelectedItem()

但是.Text返回一个空字符串，SelectedItem()返回null

以下是关于我如何填充组合框的代码。组合框值取决于另一个组合框的值。

private void cboSite_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
        BackgroundWorker bw = new BackgroundWorker();
        cboPlan.Items.Clear();
        bw.DoWork += new DoWorkEventHandler(bw_cboPlan);
        bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_cboPlanComplete);
        site = cboSite.SelectedItem.ToString();
       Busy.IsBusy = true;
        Busy.BusyContent = "Loading Products";
        bw.RunWorkerAsync();
    }

    void bw_cboPlan(object sender, DoWorkEventArgs e)
    {
        SqlConnection con = new SqlConnection(Class.GetConnectionString());
        SqlCommand scProduct = new SqlCommand("spSelectProduct", con);
        scProduct.Parameters.Add(new SqlParameter("@Site",site));
        scProduct.CommandType = CommandType.StoredProcedure;

        SqlDataReader readerPortal;
        con.Open();

        readerPortal = scProduct.ExecuteReader();

        while (readerPortal.Read())
        {
            this.Dispatcher.Invoke((Action)delegate(){cboPlan.Items.Add(readerPortal[0]);});
        }
        con.Close();
    }

    void bw_cboPlanComplete(object sender, RunWorkerCompletedEventArgs e)
    {
        cboPlan.SelectedIndex = 0;
        Busy.IsBusy = false;
    }

虽然我可以在组合框中看到.Text值，但我无法在代码中使用它们。

编辑：Null值由cboPlan Combobox返回。

以下是SelectedItem()时返回空值，.Text时返回空字符串

if (IsValid())
        {
            BackgroundWorker bw = new BackgroundWorker();
            cboPlan.Items.Clear();
            bw.DoWork += new DoWorkEventHandler(bw_Add);
            bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_AddComplete);
            plan = cboPlan.Text;
            Busy.IsBusy = true;
            Busy.BusyContent = "Sending Request.";
            bw.RunWorkerAsync();
        }

The Comboboxes的XAML。

<ComboBox x:Name="cboSite" HorizontalAlignment="Left" Margin="461,52,0,0" VerticalAlignment="Top" Width="174" SelectionChanged="cboSite_SelectionChanged"/>
<ComboBox x:Name="cboPlan" HorizontalAlignment="Left" Margin="395,106,0,0" VerticalAlignment="Top" Width="240" />

Answer 1

修改

嗯，你的代码中有这个：

BackgroundWorker bw = new BackgroundWorker(); // You will delete all items here! cboPlan.Items.Clear(); bw.DoWork += new DoWorkEventHandler(bw_Add); bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_AddComplete); // plan is String.Empty because there are no items in the combobox! plan = cboPlan.Text; Busy.IsBusy = true; Busy.BusyContent = "Sending Request."; // You will start populating combobox asynchronously here bw.RunWorkerAsync();

我不确定您要做什么，但如果您想保存控件的价值，请在调用Items.Clear()函数之前执行此操作。

原始回答

我建议您在bw_cboPlan中填写数据库中的List，并在RunWorkerCompletedEventHandler回调函数中填充ComboBox：

List<String> combovalues = new List<String>(); void bw_cboPlan(object sender, DoWorkEventArgs e) { SqlConnection con = new SqlConnection(Class.GetConnectionString()); SqlCommand scProduct = new SqlCommand("spSelectProduct", con); scProduct.Parameters.Add(new SqlParameter("@Site",site)); scProduct.CommandType = CommandType.StoredProcedure; SqlDataReader readerPortal; con.Open(); readerPortal = scProduct.ExecuteReader(); combovalues.Clear(); while (readerPortal.Read()) { combovalues.Add(readerPortal[0]); // untested //this.Dispatcher.Invoke((Action)delegate(){cboPlan.Items.Add(readerPortal[0]);}); } con.Close(); } void bw_cboPlanComplete(object sender, RunWorkerCompletedEventArgs e) { foreach(var item in combovalues) cboPlan.Items.Add(item); cboPlan.SelectedIndex = 0; Busy.IsBusy = false; }

Combobox.Text总是返回Null

1 个答案: