Question

当用户尝试在列表框中向下移动最后一项时，我需要一个消息框来显示该项目已在底部。该应用程序允许用户输入更多项目到列表，所以当达到一个数字时显示消息，如顶部，将无法工作，这是我目前的代码：

    private void MoveUpButton()
    {
        if (selectedPlayersListBox.SelectedItem == null || selectedPlayersListBox.SelectedIndex < 0)
            MessageBox.Show("A player under \"Selected Players\" must be selected");

        if (selectedPlayersListBox.SelectedIndex == 0)
            MessageBox.Show("Player is already at the top of the list.");

        else
        {
            MoveItem(-1);
        }
    }

    private void MoveDownButton()
    {
        if (selectedPlayersListBox.SelectedItem == null || selectedPlayersListBox.SelectedIndex < 0)
            MessageBox.Show("A player under \"Selected Players\" must be selected");

        else
        {
            MoveItem(1);
        }
    }

    private void MoveItem(int direction)
    {
        int newIndex = selectedPlayersListBox.SelectedIndex + direction;

        if (newIndex < 0 || newIndex >= selectedPlayersListBox.Items.Count)
            return;

        object selected = selectedPlayersListBox.SelectedItem;

        selectedPlayersListBox.Items.Remove(selected);
        selectedPlayersListBox.Items.Insert(newIndex, selected);
        selectedPlayersListBox.SetSelected(newIndex, true);
    }

正如我上面提到的，MoveUpButton运行正常，但MoveDownButton给我带来了麻烦。

感谢您提供的任何帮助。

Answer 1

它看起来就像MoveUpButton，除了你要检查SelectedIndex是否等于Count - 1：

    private void MoveDownButton()
    {
        if (selectedPlayersListBox.SelectedItem == null || selectedPlayersListBox.SelectedIndex < 0)
            MessageBox.Show("A player under \"Selected Players\" must be selected");
        else if (selectedPlayersListBox.SelectedIndex == selectedPlayersListBox.Items.Count - 1)
            MessageBox.Show("Player is already at the bottom of the list.");
        else
        {
            MoveItem(1);
        }
    }

Answer 2

向上/向下移动的另一种方式

public partial class Form1：Form {

public Form1() {
    InitializeComponent();
    btnMoveUp.Enabled = false;
    btnMoveDown.Enabled = false;
}

private void lstPlayers_SelectedIndexChanged(object sender, EventArgs e) {          
    btnMoveUp.Enabled = (lstPlayers.SelectedIndex != 0);
    btnMoveDown.Enabled = (lstPlayers.SelectedIndex != lstPlayers.Items.Count - 1);
}

    private void btnMoveUp_Click(object sender, EventArgs e) {
        var index = lstPlayers.SelectedIndex;
        var item = lstPlayers.SelectedItem;
        lstPlayers.Items.Insert(index - 1, item);
        lstPlayers.Items.RemoveAt(index + 1);
        lstPlayers.SetSelected(index - 1, true);
    }

    private void btnMoveDown_Click(object sender, EventArgs e) {
        var index = lstPlayers.SelectedIndex;
        var item = lstPlayers.SelectedItem;
        lstPlayers.Items.Insert(index + 2, item);
        lstPlayers.Items.RemoveAt(index);
        lstPlayers.SetSelected(index + 1, true);
    }       
}

当列表框中的最后一项向下移动时，如何显示消息框？

2 个答案: