Question

我有1个带有2个组合框的WinForm，第一个填充了员工姓名，第二个应该填充受第一个组合中列出的每个员工影响的任务。但无法获得以下代码来运行第二个组合：

            private void Form1_Load(object sender, EventArgs e)
        {
            using (LINQtoEntitiesEntities MyEntities = new LINQtoEntitiesEntities())
            {
                ObjectQuery<Employee> Emp = MyEntities.Employee;
                comboBox1.DataSource = (from u in Emp select new { u.ID, u.LastName }).ToList();
                comboBox1.ValueMember = "ID";
                comboBox1.DisplayMember = "LastName";
            }
        }

        private void comboBox1_TextChanged(object sender, EventArgs e)
        {
            if (comboBox1.SelectedIndex.ToString() == "0") return;
            using (LINQtoEntitiesEntities MyEntities = new LINQtoEntitiesEntities())
            {
                label1.Text = comboBox1.SelectedValue.ToString();
                ObjectQuery<Tasks> Tsk = MyEntities.Tasks;
comboBox2.DataSource = (from t in Tsk where t.EmloyeeID.ToString() == comboBox1.SelectedValue.ToString() select new { t.ID, t.TaskName }).ToList();
                comboBox2.ValueMember = "ID";
                comboBox2.DisplayMember = "TaskName";
            }
        }

可以正常填充ComboBox1，但不能填充ComboBox2，如果ComboBox1的第一行是空白的话会很棒。

Answer 1

您想要处理combobox1的SelectedIndexChanged事件，而不是TextChanged事件。

要插入空值，请尝试以下操作：

// replace the -1 with an appropriate value that matches the type of u.ID
(from u in Emp select new { u.ID, u.LastName }).ToList().Insert(0, new { -1, string.Empty });

ComboBox2上的ComboBox2更改更改 - 使用LINQ EF Winform C＃

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