如何将数据绑定对象的组合框字段绑定到数据源,同时仍然允许空值?

post and in comments

Databinding and Nullable types in WinForms.NET

也许这段绑定可为null的DateTimePicker的代码可以帮助您找到解决此问题或其他可为null问题的其他解决方案。

Dan Hannan 关于我提出扩展方法的来源。

/// <summary>
    /// From BReusable
    /// </summary>
    /// <param name="dtp"></param>
    /// <param name="dataSource"></param>
    /// <param name="valueMember"></param>
    /// <remarks>With help from Dan Hanan at http://blogs.interknowlogy.com/danhanan/archive/2007/01/21/10847.aspx</remarks>
    public static void BindNullableValue(this DateTimePicker dateTimePicker, BindingSource dataSource, String valueMember,bool showCheckBox)
    {
        var binding = new Binding("Value", dataSource, valueMember, true);

        //OBJECT PROPERTY --> CONTROL VALUE
        binding.Format += new ConvertEventHandler((sender, e) =>
        {
            Binding b = sender as Binding;

            if (b != null)
            {
                DateTimePicker dtp = (binding.Control as DateTimePicker);
                if (dtp != null)
                {
                    if (e.Value == null)
                    {

                        dtp.ShowCheckBox = showCheckBox;
                        dtp.Checked = false;

                        // have to set e.Value to SOMETHING, since it's coming in as NULL
                        // if i set to DateTime.Today, and that's DIFFERENT than the control's current
                        // value, then it triggers a CHANGE to the value, which CHECKS the box (not ok)
                        // the trick - set e.Value to whatever value the control currently has. 
                        // This does NOT cause a CHANGE, and the checkbox stays OFF.

                        e.Value = dtp.Value;

                    }
                    else
                    {
                        dtp.ShowCheckBox = showCheckBox;
                        dtp.Checked = true;
                        // leave e.Value unchanged - it's not null, so the DTP is fine with it.
                    }

                }

            }
        });
        // CONTROL VALUE --> OBJECT PROPERTY
        binding.Parse += new ConvertEventHandler((sender, e) =>
        {
            // e.value is the formatted value coming from the control. 
            // we change it to be the value we want to stuff in the object.
            Binding b = sender as Binding;

            if (b != null)
            {
                DateTimePicker dtp = (b.Control as DateTimePicker);
                if (dtp != null)
                {
                    if (dtp.Checked == false)
                    {
                        dtp.ShowCheckBox = showCheckBox;
                        dtp.Checked = false;
                        e.Value = (Nullable<DateTime>)null;
                    }
                    else
                    {
                        DateTime val = Convert.ToDateTime(e.Value);
                        e.Value = val;
                    }
                }
            }
        });
        dateTimePicker.DataBindings.Add(binding);

    }

如果您的主要目标是将组合还原为空,将值还原为null,只需在编辑行时按Ctrl+0即可。

我花了两天疯狂的研究和心脏病发作的风险,才发现这个隐藏在某个地方的小帖子里。

用于绑定到Type组合的数据源可以再有一个NULL值的条目。

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
TypeID   Name
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1        Business
2        Government
-1       NULL