c# - 组合框和 System.Data.DataRowView

Question

我有一个在主窗体打开时调用的方法

private void populateComboBoxes()
{
    SqlCeDataAdapter breakfastAdapter = new SqlCeDataAdapter("SELECT DISTINCT recipeName FROM Recipe WHERE Category = 'breakfast' ", databaseConnection);
    SqlCeDataAdapter lunchAdapter = new SqlCeDataAdapter("SELECT DISTINCT recipeName FROM Recipe WHERE Category = 'lunch' ", databaseConnection);
    breakfastAdapter.Fill(breakfastDS, "Recipe");
    lunchAdapter.Fill(lunchDS, "Recipe");
    cmbBox1.DisplayMember = "recipeName";
    cmbBox1.ValueMember = "recipeName";
    cmbBox1.DataSource = breakfastDS.Tables["Recipe"];
    cmbBox2.DataSource = lunchDS.Tables["Recipe"];            
    cmbBox2.DisplayMember = "recipeName";
    cmbBox2.ValueMember = "recipeName";                      
}

这实际上是根据 SELECT 语句填充两个组合框。一旦此方法命中 cmbBox1.DataSource = breakfastDS.Tables["Recipe"]，它就会停止执行并移至此方法:

private void cmbBox1_SelectedIndexChanged(object sender, EventArgs e)
{         
    rtbPicture.Visible = false;
    string qry = "";
    qry = "SELECT DISTINCT ingredientName FROM Recipe WHERE recipeName = " + cmbBox1.SelectedItem.ToString();

    SqlCeCommand com = new SqlCeCommand(qry, databaseConnection);
    com.CommandText = qry;
    rtbRecipe.Text = com.ExecuteScalar().ToString();
}

此方法应该执行 select 语句并将该信息放入 richtextbox，但由于某些原因未设置 cmbBox1。根据我的理解，第一个 combobox 已经在前面的方法中设置了显示和值成员。但是，当我到达 cmbBox1.SelectedItem.ToString() 时，它返回 System.Data.DataRowView 而不是 combobox 中的实际字符串.我不确定为什么它给我 System.Data.DataRowView 而不是字符串。

Answer 1

您正在使用 cmbBox1.SelectedItem.ToString()。您可能应该改用 SelectedValue:

qry = "SELECT DISTINCT ingredientName FROM Recipe WHERE recipeName = " + cmbBox1.SelectedValue.ToString();

SelectedItem 获取实际的 ComboBox 项(在本例中为 DataRowView)，而 SelectedValue 获取值您指定为 ComboBox 的 ValueMember 的属性。