System.InvalidCastException：'无法投射对象

Question

试图在组合框（下拉列表）中获取所选对象的值得到此错误：

System.InvalidCastException：'无法转换类型的对象
“ System.Collections.Generic.KeyValuePair`2 [System.String，schoolstuff.Employee]”键入“ schoolstuff.Employee”。

我试图为cboEmployees.SelectedItem找到一个“值”，但似乎没有任何值。

employees[employee.Name] = employee;

cboEmployees.DataSource = new BindingSource(employees, null);
cboEmployees.DisplayMember = "Key";
cboEmployees.ValueMember = "Value";

private void cboEmployees_SelectedIndexChanged(object sender, EventArgs e)
{
    if (cboEmployees.SelectedItem == null) return;

    var employee = (Employee)cboEmployees.SelectedItem;

    if(employee != null)
        txtName.Text = employee.Name;
}

Answer 1

cboEmployees.SelectedItem是一个KeyvaluePair<K,V> 。

因此，您不能像这样进行转换： (Employee)cboEmployees.SelectedItem

这应该起作用：

var employee = ((KeyValuePair<string,Employee>)cboEmployees.SelectedItem).Value;

或者，您可以改用SelectedValue：

    if (cboEmployees.SelectedValue == null) return;
    var employee = (Employee)cboEmployees.SelectedValue;

Answer 2

您的SelectedItem不是Employee 。

要么使用SelectedValue

var employee = (Employee)cboEmployees.SelectedValue;

或强制转换为KeyValuePair<string, Employee>

var kvp = (KeyValuePair<string, Employee>)cboEmployees.SelectedItem;
var employee = kvp.Value;