DataGridView 绑定问题：“索引 -1 没有值。”

Question

我有一个绑定到绑定源的 datagridview 和表单上的几个按钮。一个按钮将项目添加到绑定源，另一个按钮删除当前选定的项目。还有一个事件处理程序，用于侦听 CurrentChanged 事件并更新“删除”按钮的“启用”状态。

一切都很顺利，直到我从 datagridview 中删除最后一项。然后我看到一个非常丑陋的异常：

   at System.Windows.Forms.CurrencyManager.get_Item(Int32 index)
   at System.Windows.Forms.CurrencyManager.get_Current()
   at System.Windows.Forms.DataGridView.DataGridViewDataConnection.OnRowEnter(DataGridViewCellEventArgs e)
   at System.Windows.Forms.DataGridView.OnRowEnter(DataGridViewCell& dataGridViewCell, Int32 columnIndex, Int32 rowIndex, Boolean canCreateNewRow, Boolean validationFailureOccurred)
   at System.Windows.Forms.DataGridView.SetCurrentCellAddressCore(Int32 columnIndex, Int32 rowIndex, Boolean setAnchorCellAddress, Boolean validateCurrentCell, Boolean throughMouseClick)
   at System.Windows.Forms.DataGridView.SetAndSelectCurrentCellAddress(Int32 columnIndex, Int32 rowIndex, Boolean setAnchorCellAddress, Boolean validateCurrentCell, Boolean throughMouseClick, Boolean clearSelection, Boolean forceCurrentCellSelection)\r\n   at System.Windows.Forms.DataGridView.MakeFirstDisplayedCellCurrentCell(Boolean includeNewRow)
   at System.Windows.Forms.DataGridView.OnEnter(EventArgs e)
   at System.Windows.Forms.Control.NotifyEnter()
   at System.Windows.Forms.ContainerControl.UpdateFocusedControl()
   at System.Windows.Forms.ContainerControl.AssignActiveControlInternal(Control value)
   at System.Windows.Forms.ContainerControl.ActivateControlInternal(Control control, Boolean originator)
   at System.Windows.Forms.ContainerControl.SetActiveControlInternal(Control value)
   at System.Windows.Forms.ContainerControl.SetActiveControl(Control ctl)
   at System.Windows.Forms.ContainerControl.set_ActiveControl(Control value)
   at System.Windows.Forms.Control.Select(Boolean directed, Boolean forward)
   at System.Windows.Forms.Control.SelectNextControl(Control ctl, Boolean forward, Boolean tabStopOnly, Boolean nested, Boolean wrap)
   at System.Windows.Forms.Control.SelectNextControlInternal(Control ctl, Boolean forward, Boolean tabStopOnly, Boolean nested, Boolean wrap)
   at System.Windows.Forms.Control.SelectNextIfFocused()
   at System.Windows.Forms.Control.set_Enabled(Boolean value)
   at Bug3324.Form1.HandleBindingSourceCurrentChanged(Object _sender, EventArgs _e) in D:\\Dev\\TempApps\\Bug3324\\Bug3324\\Form1.cs:line 41
   at System.Windows.Forms.BindingSource.OnCurrentChanged(EventArgs e)
   at System.Windows.Forms.BindingSource.CurrencyManager_CurrentChanged(Object sender, EventArgs e)
   at System.Windows.Forms.CurrencyManager.OnCurrentChanged(EventArgs e)

我在一个小场景中隔离了这个问题：

    private BindingSource m_bindingSource = new BindingSource();

    public Form1()
    {
        InitializeComponent();

        m_bindingSource.CurrentChanged += HandleBindingSourceCurrentChanged;
        m_bindingSource.DataSource = new BindingList<StringValue>();

        dataGridView1.DataSource = m_bindingSource;

        btnAdd.Click += HandleAddClick;
        btnRemove.Click += HandleRemoveClick;
    }

    private void HandleRemoveClick(object _sender, EventArgs _e)
    {
        m_bindingSource.RemoveCurrent();
    }

    private void HandleAddClick(object _sender, EventArgs _e)
    {
        m_bindingSource.Add(new StringValue("Some string"));
    }

    private void HandleBindingSourceCurrentChanged(object _sender, EventArgs _e)
    {
        // this line throws an exception when the last item is removed from
        // the datagridview
        btnRemove.Enabled = (m_bindingSource.Current != null);

    }
}

public class StringValue
{
    public string Value { get; set; }

    public StringValue(string value)
    {
        Value = value;
    }
}

通过纯粹的实验，我发现如果我不更改 CurrentChanged 事件处理程序中的按钮状态，那么一切都会正常工作。所以我怀疑存在某种操作顺序问题。但什么？为什么尝试进行与 datagridview 完全无关的更改会导致问题？

更有趣的是，如果程序在 VS 中启动并附加了调试器，则异常通常是无害的（或根本不显示）。但如果它单独执行，则会弹出一个消息框，其中包含异常详细信息。

我尝试处理 datagridview 上的 RowEnter 事件，发现在这种情况下，它仍然认为它有一行并尝试从绑定源检索当前项，但m_bindingSource.Current已经为空。为什么只有在处理 CurrentChanged 事件时才会出现这个问题？

任何和所有的帮助将不胜感激。谢谢。

Answer 1

我最终是这样解决的：

private void HandleRemoveClick(object _sender, EventArgs _e)
{
    btnRemove.Enabled = false;
    m_bindingSource.RemoveCurrent();
}

private void HandleBindingSourceCurrentChanged(object _sender, EventArgs _e)
{
    if(m_bindingSource.Current != null)
        btnRemove.Enabled = true;
}

这有点奇怪，但似乎工作正常。