c# listview 取消选择项目

Question

我正在开发一个 Windows 应用程序，它有一个包含大量项目的 ListView。 当用户单击某个项目时，应用程序会显示该项目的详细信息。这 然后用户有机会编辑这些详细信息。用户应该点击 每次更改后的保存按钮，当然这并不总是发生。

如果用户进行更改但未单击“保存”，应用会显示一条消息 询问他们是否要保存更改的框。此框包含取消 按钮，如果他们单击取消，我想短路选择 另一项并让用户停留在他们正在编辑的项上。

我找不到执行此操作的方法，如果项目更改但未保存，我会显示 itemselecedchanged 事件的对话框，如果用户单击取消，我会从事件中删除我的功能并手动更改所选项目，然后我将函数返回给事件，但在此之后事件调用和我手动选择的项目未被选中。

    private bool EnsureSelected()
    {
        bool continue_ = true;
        if (_objectChange)
        {
            var res = MessageBox.Show("Do you want to save changes?", "Warning", MessageBoxButtons.YesNoCancel, MessageBoxIcon.Warning);
            switch (res)
            {
                case DialogResult.Cancel:
                    if (!string.IsNullOrEmpty(_selectedKey))
                    {
                        listView_Keys.ItemSelectionChanged -= listView_Keys_ItemSelectionChanged;
                        listView_Keys.Focus();
                        listView_Keys.Items[_selectedKey].Selected = true;
                        listView_Keys.ItemSelectionChanged += listView_Keys_ItemSelectionChanged;
                    }
                    continue_ = false;
                    break;
                case DialogResult.Yes:
                    button_Save.PerformClick();
                    _objectChange = false;
                    break;
                case DialogResult.No:
                    _objectChange = false;
                    break;
                default:
                    throw new ArgumentOutOfRangeException();
            }              
        }
        return continue_;
    }

更新::

我试过这个解决方案:

        public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }
    private ListViewItem currentSelection = null;
    private bool pending_changes = false;
    private void listView1_ItemSelectionChanged(object sender, ListViewItemSelectionChangedEventArgs e)
    {
        if (e.Item == currentSelection)
        {
            // if the current Item gets unselected but there are pending changes
            if (!e.IsSelected && pending_changes)
            {
                var res = MessageBox.Show("Do you want to save changes?", "Warning", MessageBoxButtons.YesNoCancel, MessageBoxIcon.Warning);
                switch (res)
                {
                    case DialogResult.Cancel:
                        // we dont want to change the selected item, so keep it selected
                        e.Item.Selected = true;
                        break;
                    case DialogResult.Yes:
                        //button_Save.PerformClick();
                        pending_changes = false;
                        break;
                    case DialogResult.No:
                        pending_changes = false;
                        break;
                    default:
                        throw new ArgumentOutOfRangeException();
                }
            }

        }
        else // not the selected button
        {
            if (!pending_changes && e.IsSelected)
            {
                // Item may be selected and we save it as the new current selection
                currentSelection = e.Item;
            }
            else if (pending_changes && e.IsSelected)
            {
                // Item may not be enabled, because there are pending changes
                e.Item.Selected = false;
            }
        }
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        listView1.Items[0].Selected = true;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        pending_changes = true;
    }
}

但这没有用，第一次挂起的更改为真时，消息框调用了两次，第二次什么也没发生。

Answer 1

首先，每当您选择另一个项目时，该事件应该触发两次。

首先针对取消选择的项目(其中 e.IsSelected 为 false)

第二个用于选择的项目(其中 e.IsSelected 为 true)

假设您设置了一个标记 pending_changes，只要有未保存的更改，下面的代码应该取消项目选择。

不幸的是，无论何时显示 MessageBox，listView 都会再次失去焦点。当您单击离开 MessageBox 时，焦点将返回到 listView 上，这会导致控件再次触发其事件。这就是为什么需要一个肮脏的解决方法，需要记住我们在消息框上单击了“取消”并再次对下一个事件执行操作。

这是包含解决方法的代码:

private ListViewItem currentSelection = null;
private bool pending_changes = false;
private bool cancel_flag = false;
private void listView1_ItemSelectionChanged(object sender, ListViewItemSelectionChangedEventArgs e)
{
    Console.WriteLine("Item " + e.ItemIndex + " is now " + e.IsSelected);
    if (e.Item != currentSelection)
    {
        // if another item gets selected but there are pending changes
        if (e.IsSelected && pending_changes)
        {
            if (cancel_flag)
            {
                // this handles the second mysterious event
                cancel_flag = false;
                currentSelection.Selected = true;
                e.Item.Selected = false;
                return;
            }
            Console.WriteLine("uh oh. pending changes.");
            var res = MessageBox.Show("Do you want to save changes?", "Warning", MessageBoxButtons.YesNoCancel, MessageBoxIcon.Warning);
            switch (res)
            {
                case DialogResult.Cancel:
                    // we dont want to change the selected item, so keep it selected
                    currentSelection.Selected = true;
                    e.Item.Selected = false;
                    // for some reason, we will get the same event with the same argments again, 
                    // after we click the cancel button, so remember our decision
                    cancel_flag = true;
                    break;
                case DialogResult.Yes:
                    // saving here. if possible without clicking the button, but by calling the method that is called to save
                    pending_changes = false;
                    currentSelection = e.Item;
                    break;
                case DialogResult.No:
                    pending_changes = false;
                    currentSelection = e.Item;
                    break;
                default:
                    throw new ArgumentOutOfRangeException();
            }
        }
        else if (e.IsSelected && !pending_changes)
        {
            currentSelection = e.Item;
        }
    }
}