c# - 将我填充的数组值显示到列表框中并可选择删除它们

Question

好的，在 Stackoverflow 上很棒的人的帮助下，我创建了这样的数组。

public partial class Form1 : Form    
{
    string[] Brands = new string[10];
    int brandNo;}

    public Form1()
    {
       InitializeComponent();
       Brands[0] = "Yamaha"; //ok
       Brands[1] = "Suzuki"; //ok
       Brands[2] = "Harley"; //ok
       Brands[3] = "Kawasaki"; //ok
       brandNo = 4;
    }

    private void buttonAddbrand_Click(object sender, EventArgs e)
    {
       if (brandNo >= 10)
          return; //cannot add more brand

       Brands[brandNo++] = textBoxMerk.Text;
       var Merk = Brands
       listBoxMotoren.Items.Clear();

       listBoxMotoren.Items.AddRange(Merk);

使用这段代码，我想在我的列表框中显示数组的填充值。但是我收到以下错误:

value can not be null.

非常感谢您的帮助。

Answer 1

首先，请注意大括号的放置位置，以确保可以编译代码。

public partial class Form1 : Form    
{
    string[] Brands = new string[10];
    int brandNo;} //<- off-placed

其次，由于您首先将数组作为您的 DataSource(而不是使用 Items.Add 或 Items.AddRange 到您的 listBoxMotoren，如果你在 listBoxMotoren 中添加或删除你的项目，它可能是一致的。

private void buttonAddbrand_Click(object sender, EventArgs e) {
    if (brandNo >= 10)
        return; //cannot add more brand

    Brands[brandNo++] = textBoxMerk.Text;
    listBoxMotoren.DataSource = null; //the cheapest and dirtiest trick to do this
    listBoxMotoren.DataSource = Brands; //Maintaining the style, use `DataSource` to accommodate new data
}

最后，如果您想随意删除品牌项目，您可能需要在 Form1 中添加另一个 Control 作为您要删除的品牌项目的输入有选择地删除。但请注意，这可能会“破坏”您的项目序列，因此您可能需要“重新排序”您的项目。

现在，假设您使用 NumericUpDown 删除并使用 buttonDeletebrand 触发删除，那么您应该这样做

private void buttonDeletebrand_Click(object sender, EventArgs e) {
    int indexToDelete = (int)numericUpDownMotorenNumberDeleted.Value; //note the casting to (int)
    if (indexToDelete < 0 || indexToDelete >= brandNo || brandNo <= 0) //can only delete index no [0] to [brandNo-1], and if the brand no > 0
        return; //invalid index
    for (int i = indexToDelete; i < brandNo - 1; ++i)
        Brands[indexToDelete] = Brands[indexToDelete + 1]; //resequencing
    Brands[brandNo - 1] = string.Empty; //removes the last element after resequencing
    listBoxMotoren.DataSource = null; //remember the cheapest and dirtiest trick?
    listBoxMotoren.DataSource = Brands;
    --brandNo; //reduce the brandNo by 1
}

总的来说，您需要将所有这些结合起来:

public partial class Form1 : Form {
    string[] Brands = new string[10];
    int brandNo;
    public Form1() {
        InitializeComponent();
        Brands[0] = "Yamaha";
        Brands[1] = "Suzuki";
        Brands[2] = "Harley";
        Brands[3] = "Kawasaki";
        brandNo = 4;
        listBoxMotoren.DataSource = Brands;
    }

    private void buttonAddbrand_Click(object sender, EventArgs e) {
        if (brandNo >= 10)
            return;

        Brands[brandNo++] = textBoxMerk.Text;
        listBoxMotoren.DataSource = null;
        listBoxMotoren.DataSource = Brands;
    }

    private void buttonDeletebrand_Click(object sender, EventArgs e) {
        int indexToDelete = (int)numericUpDownMotorenNumberDeleted.Value;
        if (indexToDelete < 0 || indexToDelete >= brandNo || brandNo <= 0)
            return;
        for (int i = indexToDelete; i < brandNo - 1; ++i)
            Brands[indexToDelete] = Brands[indexToDelete + 1];
        Brands[brandNo - 1] = string.Empty;
        listBoxMotoren.DataSource = null;
        listBoxMotoren.DataSource = Brands;
        --brandNo;
    }
}