Question

我有一个在打开主窗体时调用的方法

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";                      
}

基本上根据SELECT语句填充两个组合框。一旦此方法命中cmbBox1.DataSource = breakfastDS.Tables["Recipe"]，它就会停止执行并转移到此方法：

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语句并将该信息放在richtextbox中，但由于某种原因cmbBox1未设置。根据我的理解，第一个combobox已经在前一个方法中设置了显示和值成员。但是，当我到达cmbBox1.SelectedItem.ToString()时，它会返回System.Data.DataRowView而不是combobox中的实际字符串。我不确定为什么它会给我System.Data.DataRowView而不是字符串。

Answer 1

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

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获取您指定为ValueMember的属性的值ComboBox。

Answer 2

cmbBox2.DisplayMember =“recipeName”;

cmbBox2.DataSource = lunchDS.Tables [“Recipe”];

cmbBox2.ValueMember =“recipeName”;

Combobox和System.Data.DataRowView

2 个答案: