Question

我有一个组合框，我在其中设置了DataSource Value，但是当我尝试设置SelectedValue时，ComboBox返回null。所以请帮忙。

BindingList<KeyValuePair<string, int>> m_items =
                     new BindingList<KeyValuePair<string, int>>();

for (int i = 2; i <= 12; i++)
    m_items.Add(new KeyValuePair<string, int>(i.ToString(), i));
ComboBox cboGridSize = new ComboBox();
cboGridSize.DisplayMember = "Key";
cboGridSize.ValueMember = "Value";
cboGridSize.DataSource = m_items;

cboGridSize.SelectedValue = 4;

当我将SelectedValue设置为4时，它返回NULL。

Answer 1

同意@Laazo更改为字符串。

cboGridSize.SelectedValue = "4";

或与此类似的东西

int selectedIndex = comboBox1.SelectedIndex;
Object selectedItem = comboBox1.SelectedItem;

MessageBox.Show("Selected Item Text: " + selectedItem.ToString() + "\n" +
"Index: " + selectedIndex.ToString());

并参考这看起来好像对你的问题有好处：

Answer 2

我在尝试解决此问题的同时遇到了这个问题。我通过创建以下扩展方法解决了该问题。

        public static void ChooseItem<T>(this ComboBox cb, int id) where T : IDatabaseTableClass
    {
        // In order for this to work, the item you are searching for must implement IDatabaseTableClass so that this method knows for sure
        // that there will be an ID for the comparison.

        /* Enumerating over the combo box items is the only way to set the selected item.
         * We loop over the items until we find the item that matches. If we find a match,
         * we use the matched item's index to select the same item from the combo box.*/
        foreach (T item in cb.Items)
        {
            if (item.ID == id)
            {
                cb.SelectedIndex = cb.Items.IndexOf(item);
            }
        }
    }

我还创建了一个名为IDatabaseTableClass的接口（可能不是最佳名称）。该接口具有一个属性，即int ID {get;组; }为了确保我们确实有一个ID可以与参数中的int id进行比较。

如何在Combobox中设置Selectedvalue c＃

2 个答案: