c# - 使用 ComboBox.SelectedItem = -1 时 ComboBox 不加载空白值

Question

我有一个组合框，可以正确加载我从数据库查询的数据列表，我唯一的问题是我似乎无法让它加载空白并强制用户从列表中选择(然后推送 SelectedIndexChanged() 方法下的操作)。通过我的搜索，我发现我可以在哪里简单地将 SelectedItem 值更改为 -1，这应该会在空选项上加载组合框，但是当我使用这段代码时，我看不出有什么不同。 comboBox 仍会正确加载列表，但仍会显示列表中的第一个条目。

private void loadPatientList()
    {
        comboBox_PatientSelect.DataSource = patientList.Distinct().ToList();
        comboBox_PatientSelect.DisplayMember = "displayFullName";
        comboBox_PatientSelect.ValueMember = "patientID";
        comboBox_PatientSelect.SelectedItem = -1;
    }

我很感激任何帮助 - 如果需要，我很乐意提供更多信息。提前致谢!

Answer 1

您要查找的属性是 SelectedIndex。所以让它 comboBox_PatientSelect.SelectedIndex = -1;

来自 MSDN:

This property indicates the zero-based index of the currently selected item in the combo box list. Setting new index raises the SelectedIndexChanged event.

SelectedIndex, SelectedValue, and FormattingEnabled are related as follows:

• If FormattingEnabled is false, SelectedIndex will not be set to -1 when SelectedValue is blank.
• If FormattingEnabled is true, SelectedIndex will be set to -1 when SelectedValue is blank.

NOTE:

To deselect the currently selected item, set the SelectedIndex to -1. You cannot set the SelectedIndex of a ComboBox item to -1 if the item is a data-bound item.