如果不能新增重複項，如下

private void AddItem_Click(object sender, EventArgs e)

{

string addItem = textBox1.Text.Trim();

if (!string.IsNullOrEmpty(addItem) && !listBox1.Items.Contains(addItem))

{

listBox1.Items.Add(addItem);

}

}

private void RemoveItem_Click(object sender, EventArgs e)

{

string removeItem = textBox1.Text.Trim();

if (!string.IsNullOrEmpty(removeItem) && listBox1.Items.Contains(removeItem))

{

listBox1.Items.Remove(removeItem);

}

}

如果可以新增重複項，如下

新增：把AddItem_Click中!listBox1.Items.Contains(addItem)刪了

private void RemoveItem_Click(object sender, EventArgs e)

{

string removeItem = textBox1.Text.Trim();

if (!string.IsNullOrEmpty(removeItem))

{

while (listBox1.Items.Contains(removeItem))

{

listBox1.Items.Remove(removeItem);

}

}

}