[英]Unable to transfer Selected Items of a ListBox to another ListBox
I am unable to transfer the Selected Items from one ListBox to another ListBox: 我无法将选定的项目从一个列表框传输到另一个列表框:
protected void Button2_Click(object sender, EventArgs e)
{
foreach (ListItem li in ListBox2.Items)
{
if (li.Selected)
{
ListItem liNew = new ListItem(li.Text, li.Value);
ListBox1.Items.Add(liNew);
ListBox2.Items.Remove(liNew);
}
}
}
I am getting the exception: 我得到了例外:
System.InvalidOperationException: Collection was modified;
System.InvalidOperationException:集合已修改; enumeration operation may not execute.
枚举操作可能无法执行。
The problem is that you can't remove elements from a collection while you're iterating it. 问题在于,您无法在迭代集合时从集合中删除元素。 Instead, you can select the items that are selected :) and loop over them.
相反,您可以选择所选的项目:)并在它们上循环。
foreach(ListItem li in ListBox2.Items.Where(x => x.Selected)) {
ListItem liNew = new ListItem(li.Text, li.Value);
ListBox1.Items.Add(liNew);
ListBox2.Items.Remove(li);
}
(Also, I think you meant li
, not liNew
.) (另外,我认为您的意思是
li
,不是liNew
。)
Without LINQ, it might look like: 没有LINQ,它可能看起来像:
List<ListItem> toRemove = new List<ListItem>();
foreach(ListItem li in ListBox2.Items) {
if(li.Selected) {
ListItem liNew = new ListItem(li.Text, li.Value);
ListBox1.Items.Add(liNew);
toRemove.Add(li);
}
}
foreach(ListItem li in toRemove) {
ListBox2.Items.Remove(li);
}
Also, you can use a for
loop, as suggested by @Steve: 另外,可以使用@Steve建议的
for
循环:
for(int i = ListBox2.Items.Count; --i >= 0;) {
ListItem li = ListBox2.Items[i];
if(li.Selected) {
ListItem liNew = new ListItem(li.Text, li.Value);
ListBox1.Items.Add(liNew);
ListBox2.Items.RemoveAt(i);
}
}
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