Question

我有两个相关的组合框，combobox1填充了combobox2的项目。在combobox1 selectIndexChanged事件中，我有这段代码，但我有错误Unknown column 'System.Data.DataRowView' in 'where clause'。

我尝试在第一次选择时将此代码放入SelectionChangeCommitted，它会填充正确的项目，但我的第二次选择我在comboBox2.Items.Clear();州Items collection cannot be modified when the DataSource property is set.中出错:(怎么办）？

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    string sql;
    if (comboBox1.SelectedIndex >= 0)
    {
        comboBox2.Items.Clear();
        MySqlConnection conn = new MySqlConnection(sqlString);
        MySqlDataAdapter adapter = new MySqlDataAdapter();
        sql = "SELECT brgyname,idbrgy from barangay where idmun=" + comboBox1.SelectedValue;
        adapter.SelectCommand = new MySqlCommand(sql, conn);
        DataTable cbBrgy = new DataTable();
        adapter.Fill(cbBrgy);
        comboBox2.DataSource = cbBrgy;
        comboBox2.DisplayMember = "brgyname";
        comboBox2.ValueMember = "idbrgy";
    }
}

以下是我如何填充combobox1

   private void cbMun()
    {
        MySqlConnection conn = new MySqlConnection(sqlString);
        MySqlDataAdapter adapter = new MySqlDataAdapter();
        adapter.SelectCommand = new MySqlCommand("SELECT munname,idmun from municipality", conn);
        DataTable cbMun = new DataTable();
        adapter.Fill(cbMun);
        comboBox1.DataSource = cbMun;
        comboBox1.DisplayMember = "munname";
        comboBox1.ValueMember = "idmun";
    }

Answer 1

当cbMun函数填充组合框时，它将直接调用组合框选择的索引更改事件，因此要解决此定义bool值comboisloading = true并修改您的代码，如下所示：

    private void cbMun()
    {
        MySqlConnection conn = new MySqlConnection(sqlString);
        MySqlDataAdapter adapter = new MySqlDataAdapter();
        adapter.SelectCommand = new MySqlCommand("SELECT munname,idmun from municipality", conn);
        DataTable cbMun = new DataTable();
        adapter.Fill(cbMun);
        comboBox1.DataSource = cbMun;
        comboBox1.DisplayMember = "munname";
        comboBox1.ValueMember = "idmun";
        comboisloading = false;
    }

    private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (comboisloading)
            return;

        string sql;
        if (comboBox1.SelectedIndex >= 0)
        {
            comboBox2.Items.Clear();
            MySqlConnection conn = new MySqlConnection(sqlString);
            MySqlDataAdapter adapter = new MySqlDataAdapter();
            sql = "SELECT brgyname,idbrgy from barangay where idmun=" + comboBox1.SelectedValue;
            adapter.SelectCommand = new MySqlCommand(sql, conn);
            DataTable cbBrgy = new DataTable();
            adapter.Fill(cbBrgy);
            comboBox2.DataSource = cbBrgy;
            comboBox2.DisplayMember = "brgyname";
            comboBox2.ValueMember = "idbrgy";
        }
    }

Answer 2

我只是将我的代码放在comboBox1_SelectionChangeCommitted而不是comboBox1_SelectedIndexChanged事件中，因为除非用户将更改提交给项目，否则仍然不生成comboBox1.SelectedValue。同样来自Items collection cannot be modified when the DataSource property is set的{{1}}错误我刚刚删除了这行代码。我仍然清理并正确更换我的combobox2物品。嗯..因为我曾经在vb中清除组合框。我想知道。

comboBox2.Items.Clear();

Visual c＃相对动态的组合框

2 个答案: