C# 如何在web表单中将项目从一个列表框添加到另一个列表框

我有两个列表框和一个按钮。我需要添加选定的项目从一个列表框到另一个点击按钮

这是按钮的代码

protected void ASPxButton4_Click(object sender, EventArgs e)
    {
        if (listBoxSubeKiyaslama1.SelectedIndex > -1)
        {
            listBoxSubeKiyaslama2.Items.Add(listBoxSubeKiyaslama1.SelectedItem);
            listBoxSubeKiyaslama2.Items.RemoveAt(listBoxSubeKiyaslama1.SelectedIndex);
            listBoxSubeKiyaslama2.UnselectAll();
        }
    }

---

单击该按钮时，我看到listBoxSubeKiyaslama1.SelectedIndex始终为“-1”。因为我认为它会从第一个列表框中回发和清除项目。如何修复此问题？

能否尝试以下代码：

    if (listBoxSubeKiyaslama1.SelectedItem != null)
    {
        listBoxSubeKiyaslama2.Items.Add(listBoxSubeKiyaslama1.SelectedItem);
        listBoxSubeKiyaslama2.Items.RemoveAt(listBoxSubeKiyaslama1.SelectedIndex);
        listBoxSubeKiyaslama2.UnselectAll();
    }

如果

EnableViewState=false

，控件将不会保存回发上的值。默认情况下，这是真的。请确保未将其设置为

false

我还建议您将控件放在

UpdatePanel

中，以避免完全回发

比如：

---

请尝试以下代码：-

ASPX.CS

public string GetSelectedItems(ListBox control)
    {
        var items = new StringBuilder();
        foreach (ListItem item in control.Items)
        {
            if (item.Selected)
                items.Append(string.Format("{0},", item.Value));
        }
        return items.ToString().Trim().TrimEnd(',');
    }
    protected void btnMoveRight_Click(object sender, EventArgs e)
    {
        for (int i = lbCourses1.Items.Count - 1; i >= 0; i--)
        {
            if (lbCourses1.Items[i].Selected == true)
            {
                lbCourses2.Items.Add(lbCourses1.Items[i]);
                ListItem li = lbCourses1.Items[i];
                lbCourses1.Items.Remove(li);
            }
        }
    }
    protected void btnMoveLeft_Click(object sender, EventArgs e)
    {
        for (int i = lbCourses2.Items.Count - 1; i >= 0; i--)
        {
            if (lbCourses2.Items[i].Selected == true)
            {
                lbCourses1.Items.Add(lbCourses2.Items[i]);
                ListItem li = lbCourses2.Items[i];
                lbCourses2.Items.Remove(li);
            }
        }
    }

    var selectedValues =  GetSelectedItems(lb2);

ASPX

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<div>
            <asp:Label ID="lbl1" runat="server" Text="lbl1:"></asp:Label>
            <asp:ListBox ID="lb1" runat="server" SelectionMode="Multiple"></asp:ListBox>
            <asp:Button Runat="server" ID="btnMoveRight" Text=">>" 
            onclick="btnMoveRight_Click"></asp:Button>
            <asp:Button Runat="server" ID="btnMoveLeft" Text="<<" 
            onclick="btnMoveLeft_Click"></asp:Button>
            <asp:ListBox ID="lb2" runat="server" SelectionMode="Multiple"></asp:ListBox>
        </div>
</ContentTemplate>
</asp:UpdatePanel>

I make it EnableViewState=true的可能重复项，但仍然不起作用。这很奇怪，请遵循教程：

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<div>
            <asp:Label ID="lbl1" runat="server" Text="lbl1:"></asp:Label>
            <asp:ListBox ID="lb1" runat="server" SelectionMode="Multiple"></asp:ListBox>
            <asp:Button Runat="server" ID="btnMoveRight" Text=">>" 
            onclick="btnMoveRight_Click"></asp:Button>
            <asp:Button Runat="server" ID="btnMoveLeft" Text="<<" 
            onclick="btnMoveLeft_Click"></asp:Button>
            <asp:ListBox ID="lb2" runat="server" SelectionMode="Multiple"></asp:ListBox>
        </div>
</ContentTemplate>
</asp:UpdatePanel>