[英]How to deselect item of listbox?
I have a ListBox
that when an item is selected, it is shown in a label as well. 但是,當我想刪除所選項目時,程序會中斷並顯示NullReferenceException
。
我的代碼:
private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
{
label1.Text = "Your Selected: " + listBox1.SelectedItem.ToString();
}
private void button2_Click(object sender, EventArgs e)
{
label1.Text = "";
listBox1.Items.RemoveAt(listBox1.SelectedIndex);
}
可能會出現列表框中沒有選定項目,因此您必須檢查:
private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
{
label1.Text = null == listBox1.SelectedItem
? ""
: "Your Selected: " + listBox1.SelectedItem.ToString();
}
private void button2_Click(object sender, EventArgs e) {
// Looks redundant, listBox1_SelectedIndexChanged will do
//label1.Text = "";
// Deselect item, but not remove it
if (listBox1.SelectedIndex >= 0)
listBox1.SelectedIndex = -1;
// In case you want to remove the item (not deselect) - comment out the code below
// if (listBox1.SelectedIndex >= 0)
// listBox1.Items.RemoveAt(listBox1.SelectedIndex);
}
編輯:至於計算列表框項目,當前列表框實現中沒有此事件。 所以你必須手動完成:
if (listBox1.SelectedIndex >= 0) {
listBox1.Items.RemoveAt(listBox1.SelectedIndex);
lbItemsCount.Text = listBox1.Items.Count.ToString();
}
另一種方法是使用列表框的單擊事件,如果我們不想雙擊一個列表框項來取消選擇另一個列表項。 前任:
private void ListBox_Right_Click(strong textobject sender, EventArgs e)
{
Btn_Left.Enabled = ListBox_Right.SelectedIndex >= 0;
ListBox_Left.ClearSelected(); // to clear the list selection/highlight
Btn_Right.Enabled = false; // for my specification
}
}
private void ListBox_Left_Click(object sender, EventArgs e)
{
Btn_Right.Enabled = ListBox_Left.SelectedIndex >= 0;
ListBox_Right.ClearSelected(); //to clear the list selection/highlight
Btn_Left.Enabled = false;// for my specification
}
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.