如何防止SelectedIndexChanged事件在从ListBox中删除项后在其中激发

本文关键字：删除 在其中 ListBox SelectedIndexChanged 何防止 事件 | 更新日期: 2023-09-27 18:20:00

我正在选择一个项目，这将导致删除所选项目。问题是，当我删除一个项目时，我选择了导致另一个删除的附加项目。。。

删除所选项目后，如何取消选择/取消选择？

这导致了我的问题：

    void lbMessage_SelectedIndexChanged(object sender, EventArgs e)
    {
        DialogResult result = new DialogResult();
        result = MessageBox.Show("Are you sure you want to remove this item?", "Removal Confirmation", MessageBoxButtons.YesNo, MessageBoxIcon.Information);
        if (result == DialogResult.Yes)
        {
            lbMessage.Items.Remove(lbMessage.SelectedItem); 
            lbMessage.SelectedIndex = -1;
        }
        else
        {
        }
    }
    private void btnAddMessage_Click(object sender, EventArgs e)
    {
        lbMessage.Items.Add(txtMessage.Text);
        txtMessage.Text = string.Empty;
    }

如何防止SelectedIndexChanged事件在从ListBox中删除项后在其中激发

在删除项目之前尝试删除SelectedIndexChanged事件，然后将其添加回：

private void lbMessage_SelectedIndexChanged(object sender, EventArgs e) {
  if (MessageBox.Show("Are you sure you want to remove this item?", 
                      "Remove Confirmation", 
                      MessageBoxButtons.YesNo,
                      MessageBoxIcon.Question) == DialogResult.Yes) {
    lbMessage.SelectedIndexChanged -= lbMessage_SelectedIndexChanged;
    lbMessage.Items.Remove(lbMessage.SelectedItem);
    lbMessage.SelectedIndexChanged += lbMessage_SelectedIndexChanged;
  }
}

设置SelectedIndex = -1会引发SelectedIndexChanged事件。检查事件开始时是否未选择任何内容。

void lbMessage_SelectedIndexChanged(object sender, EventArgs e) 
{
    if (lbMessage.SelectedIndex == -1) return;
    ...
}

如果你喜欢不带删除按钮的方式，那么就这样做：

bool isAfterDelete = false;
void lbMessage_SelectedIndexChanged(object sender, EventArgs e)
{
    if (isAfterDelete)
    {
        isAfterDelete = false;
        return;
    }
    DialogResult result = new DialogResult();
    result = MessageBox.Show("Are you sure you want to remove this item?", 
                             "Removal Confirmation", 
                             MessageBoxButtons.YesNo, 
                             MessageBoxIcon.Information);
    if (result == DialogResult.Yes)
    {
        lbMessage.Items.Remove(lbMessage.SelectedItem); 
        isAfterDelete = true;
        lbMessage.SelectedIndex = -1;
    }
    else
    {
    }
}

如果你只是在if（）中包装你的代码，检查lbMessage.SelectedIndex==-1，或者在开头写一个检查，如果它是真的，返回：

void lbMessage_SelectedIndexChanged(object sender, EventArgs e)
{
  if(lbMessage.SelectedIndex == -1)
    return;
    DialogResult result = new DialogResult();
    result = MessageBox.Show("Are you sure you want to remove this item?", "Removal Confirmation", MessageBoxButtons.YesNo, MessageBoxIcon.Information);
    if (result == DialogResult.Yes)
    {
        lbMessage.Items.Remove(lbMessage.SelectedItem); 
        lbMessage.SelectedIndex = -1;
    }
}

从Items集合中删除项目的剪切行为会导致项目更改其索引。因此，这会在列表框上再次调用"SelectedIndexChanged"事件。为了防止这种情况，您需要在remove函数之前设置一个标志，以指示在删除并防止事件发生。你可以通过以下方式来做到这一点。

    private bool afterRemove = false;
    void lbMessage_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (afterRemove)
        {
            afterRemove = false;
            return;
        }
        DialogResult result = new DialogResult();
        result = MessageBox.Show("Are you sure you want to remove this item?", "Removal Confirmation", MessageBoxButtons.YesNo, MessageBoxIcon.Information);
        if (result == DialogResult.Yes)
        {
            afterRemove = true;
            lbMessage.Items.Remove(lbMessage.SelectedItem); 
            // Another call to "lbMessage_SelectedIndexChanged" is made right here.
       }
    }
    private void btnAddMessage_Click(object sender, EventArgs e)
    {
        lbMessage.Items.Add(txtMessage.Text);
        txtMessage.Text = string.Empty;
    }

一个可能更容易理解的替代方案可以是以下内容。

    private bool afterRemove = false;
    void lbMessage_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (afterRemove)
            return;
        DialogResult result = new DialogResult();
        result = MessageBox.Show("Are you sure you want to remove this item?", "Removal Confirmation", MessageBoxButtons.YesNo, MessageBoxIcon.Information);
        if (result == DialogResult.Yes)
        {
            afterRemove = true;
            lbMessage.Items.Remove(lbMessage.SelectedItem); 
            // Another call to "lbMessage_SelectedIndexChanged" is made right here.
            afterRemove = false;
       }
    }
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