c# listview取消选择项目
本文关键字：项目 选择 取消 listview | 更新日期: 2023-09-27 17:50:17
我在一个Windows应用程序，有一个ListView包含一堆项目。当用户点击一件商品时，应用程序会显示该商品的详细信息。的然后用户就有机会编辑这些详细信息。用户应该点击保存按钮，但当然这并不总是发生。
如果用户做了更改而没有点击保存，应用程序会显示一条消息框询问是否要保存更改。此框包含"取消"选项按钮，如果他们点击取消，我想缩短选择另一个条目，并保持用户在他们正在编辑的条目。
我找不到这样做的方法，如果项目更改而不保存，我显示itemselecedchanged事件的对话框，如果用户单击取消，我从事件中删除我的函数并手动更改所选项目，之后我将函数返回到事件，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::
我尝试了这个解决方案:
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;
}
}
但是这不起作用，第一次pending changes为true时消息框调用了两次，第二次什么也没发生
首先，当您选择另一个项目时，该事件应该触发两次。
首先表示被取消选中的项目(其中e.IsSelected为false)
第二个被选中的项目(其中e.IsSelected为true)
假设您设置了一个标志pending_changes，每当有未保存的更改时，下面的代码应该取消项选择。
不幸的是，无论何时显示MessageBox, listView都会再次失去焦点。当您将MessageBox移开时，焦点会回到listView上，这将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案，需要记住我们在消息框上单击"取消"并再次对下一个事件执行操作。
下面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;
}
}
}
您可以重新选择项目并保持布尔标志中的当前状态，以避免导致不必要的代码运行(如重新加载所选项目的值，如果它实际上没有改变)。
另一种方法是处理LVN_ITEMCHANGING事件，不幸的是，在WinForms中没有实现。您可以在MSDN论坛的ListView项目更改事件线程中找到支持此事件并允许阻止更改选择的扩展列表视图类。
using System;
using System.ComponentModel;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Windows.Forms;
public partial class Form1 : Form
{
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
public Form1()
{
ListViewEx listView;
Controls.Add(listView = new ListViewEx { Dock = DockStyle.Fill, Items = { "One", "Two", "Three" } });
listView.ItemSelectionChanging += (s, e) =>
{
if (e.Index == 1)
e.Cancel = true;
Debug.WriteLine(e);
};
}
}
public class ItemSelectionChangingEventArgs : CancelEventArgs
{
public int Index { get; private set; }
public bool NewValue { get; private set; }
public bool CurrentValue { get; private set; }
public ItemSelectionChangingEventArgs(int index, bool newValue, bool currentValue)
{
Index = index;
NewValue = newValue;
CurrentValue = currentValue;
}
public override string ToString()
{
return String.Format("Index={0}, NewValue={1}, CurrentValue={2}", Index, NewValue, CurrentValue);
}
}
public class ListViewEx : ListView
{
private static readonly Object ItemSelectionChangingEvent = new Object();
public event EventHandler<ItemSelectionChangingEventArgs> ItemSelectionChanging
{
add { Events.AddHandler(ItemSelectionChangingEvent, value); }
remove { Events.RemoveHandler(ItemSelectionChangingEvent, value); }
}
protected virtual void OnItemSelectionChanging(ItemSelectionChangingEventArgs e)
{
EventHandler<ItemSelectionChangingEventArgs> handler =
(EventHandler<ItemSelectionChangingEventArgs>)Events[ItemSelectionChangingEvent];
if (handler != null)
handler(this, e);
}
protected override void WndProc(ref Message m)
{
if (m.Msg == 0x2000 + 0x004E) // [reflected] WM_NOTIFY
{
uint nmhdrCode = (uint)Marshal.ReadInt32(m.LParam, NmHdrCodeOffset);
if (nmhdrCode == LVN_ITEMCHANGING)
{
NMLISTVIEW nmlv = (NMLISTVIEW)Marshal.PtrToStructure(m.LParam, typeof(NMLISTVIEW));
if ((nmlv.uChanged & LVIF_STATE) != 0)
{
bool currentSel = (nmlv.uOldState & LVIS_SELECTED) == LVIS_SELECTED;
bool newSel = (nmlv.uNewState & LVIS_SELECTED) == LVIS_SELECTED;
if (newSel != currentSel)
{
ItemSelectionChangingEventArgs e = new ItemSelectionChangingEventArgs(nmlv.iItem, newSel, currentSel);
OnItemSelectionChanging(e);
m.Result = e.Cancel ? (IntPtr)1 : IntPtr.Zero;
return;
}
}
}
}
base.WndProc(ref m);
}
const int LVIF_STATE = 8;
const int LVIS_FOCUSED = 1;
const int LVIS_SELECTED = 2;
const uint LVN_FIRST = unchecked(0U - 100U);
const uint LVN_ITEMCHANGING = unchecked(LVN_FIRST - 0);
const uint LVN_ITEMCHANGED = unchecked(LVN_FIRST - 1);
static readonly int NmHdrCodeOffset = IntPtr.Size * 2;
[StructLayout(LayoutKind.Sequential)]
struct NMHDR
{
public IntPtr hwndFrom;
public IntPtr idFrom;
public uint code;
}
[StructLayout(LayoutKind.Sequential)]
struct NMLISTVIEW
{
public NMHDR hdr;
public int iItem;
public int iSubItem;
public int uNewState;
public int uOldState;
public int uChanged;
public IntPtr lParam;
}
}