Question

在dropdownlist1上选择第1项时，在dropdownlist2上以星号“ 02”和“ 03”标记的项应被禁用，而在dropdownlist1上选择dropdownlist2的项2则以“ 01”开头的项和“ 03”应该被禁用

protected void Page_Load(object sender, EventArgs e)
{
    if (DropDownList1.SelectedItem.Value == "01")
    {
        DropDownList2.Items.Cast<ListItem>()
        .Where(x => (x.Value.Substring(0, 2) == "02") || (x.Value.Substring(0, 2) == "03"))
        .ToList()
        .ForEach(x => x.Enabled = false);
    }
    else
    {
        DropDownList2.Items.Cast<ListItem>()
        .Where(x => (x.Value.Substring(0, 2) == "02") || (x.Value.Substring(0, 2) == "03"))
        .ToList()
        .ForEach(x => x.Enabled = true);

        if (DropDownList1.SelectedItem.Value == "02")
        {
            DropDownList2.Items.Cast<ListItem>()
            .Where(x => (x.Value.Substring(0, 2) == "01") || (x.Value.Substring(0, 2) == "03"))
            .ToList()
            .ForEach(x => x.Enabled = false);
        }
        else
        {
            DropDownList2.Items.Cast<ListItem>()
            .Where(x => (x.Value.Substring(0, 2) == "01") || (x.Value.Substring(0, 2) == "03"))
            .ToList()
            .ForEach(x => x.Enabled = true);
        }
    }
}

protected void DropDownList1_ItemChanged(object sender, EventArgs e)
{
    if (DropDownList1.SelectedItem.Value == "01")
    {
        DropDownList2.Items.Cast<ListItem>()
        .Where(x => (x.Value.Substring(0, 2) == "02") || (x.Value.Substring(0, 2) == "03"))
        .ToList()
        .ForEach(x => x.Enabled = false);
    }
    else
    {
        DropDownList2.Items.Cast<ListItem>()
        .Where(x => (x.Value.Substring(0, 2) == "02") || (x.Value.Substring(0, 2) == "03"))
        .ToList()
        .ForEach(x => x.Enabled = true);

        if (DropDownList1.SelectedItem.Value == "02")
        {
            DropDownList2.Items.Cast<ListItem>()
            .Where(x => (x.Value.Substring(0, 2) == "01") || (x.Value.Substring(0, 2) == "03"))
            .ToList()
            .ForEach(x => x.Enabled = false);
        }
        else
        {
            DropDownList2.Items.Cast<ListItem>()
            .Where(x => (x.Value.Substring(0, 2) == "01") || (x.Value.Substring(0, 2) == "03"))
            .ToList()
            .ForEach(x => x.Enabled = true);
        }
    }
}

页面加载按预期工作，正确显示了dropdownlist2上的项目，但是一旦我将dropdownlist1上的项目更改为item2并再次更改为item1，dropdownlist2根本不显示任何内容，但是dropdownlist1上的item2正常运行一般。

Answer 1

就像格雷格所说，您应该学习调试。

这就是你在做什么。

您在第二个列表框中获得了一个项目列表：

01, 02, 03

步骤1-在列表框1中选择01：停用02和03

ListBox2.Items = { 01 }

步骤2-在列表框1中选择03：激活02和03，停用01和03

ListBox2.Items = { 02 }

步骤3-在列表框1中选择01：停用02和03

ListBox2.Items = { }

结果：您忘了在一开始就激活所有内容。

更简单的解决方案

每次为每个元素设置Enabled。这样一来，您无需在更改状态之前就可以担心状态。而且它更短。.

protected void DropDownList1_ItemChanged(object sender, EventArgs e)
{
    DropDownList2.Items.Cast<ListItem>()
        .ToList()
        .ForEach(x => x.Enabled = (DropDownList1.SelectedItem.Value == x.Value.Substring(0, 2)));
}

如果语句未执行部分代码

1 个答案:

这就是你在做什么。

更简单的解决方案