错误是因为您的演员表无法正常工作:

The error is because your cast isn''t working:

(dataGridView1.Columns[4] as DataGridViewComboBoxColumn).DataSource

http://msdn.microsoft.com/en-us/library/cscsdfbt％28v = vs.71％29.aspx [ ^ ]

如果这种类型的转换不起作用，它只会返回null，因此您试图在一个null对象上设置.DataSource属性.

我不能说为什么强制转换不起作用，但是在强制转换之前，您需要检查dataGridView1.Columns[4]不为空，并且dataGridView1.Columns[4]是DataGridViewComboBoxColumn类型.

http://msdn.microsoft.com/en-us/library/cscsdfbt%28v=vs.71%29.aspx[^]

If this type of cast doesn''t work, it simply returns null, so you''re trying to set the .DataSource property on an object that is null.

I can''t say why the cast isn''t working but you need to check that dataGridView1.Columns[4] is not null and that dataGridView1.Columns[4] is of type DataGridViewComboBoxColumn before you cast.