Question

好的，所以在Stackoverflow上有很棒的人帮助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);

使用此代码，我想在列表框中显示数组的填充值。但是我收到以下错误：

值不能为null。

非常感谢帮助。

Answer 1

我很确定这段代码甚至无法编译....

   int brandNo;} <- "}" ???

   var Merk = Brands <- ";" missing and (var Merk) not needed

锁定此代码我猜问题是在检查

if (listBoxMotoren != null && listBoxMotoren.Items.Any()) 
       listBoxMotoren.Items.Clear();

和cource

if (listBoxMotoren != null && Brands  != null)
   listBoxMotoren.Items.AddRange(Brands);

如果listboxMotoren为null，则表单尚未初始化，因为listBoxMotoren是表单控件

Answer 2

  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;
        listBoxMotoren.DataSource=Brands;//asssiign the current list to //listbox
    }

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

   Brands[brandNo++] = textBoxMerk.Text;

   listBoxMotoren.DataSource = null; //make the list empty
   listBoxMotoren.DataSource = Brands;// assgin it new list
    }

Answer 3

首先，请注意放置花括号的位置，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，既然您开始将数组作为DataSource（并且不使用Items.Add或Items.AddRange添加到listBoxMotoren，那么如果您这样做则可能是一致的在listBoxMotoren。

中添加或删除您的商品

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，如果您想要随意删除品牌商品，则可能需要在Control中另外Form1作为输入，以便您可以选择删除品牌中的哪个商品。但请注意，这可能会“破坏”您的物品序列，因此您可能需要对物品进行“重新排序”。

现在，假设你使用NumericUpDown删除并使用buttonDeletebrand触发删除，那么你应该做这样的事情

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，你需要将它们全部合并起来：

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;
    }
}

将填充的数组值显示在列表框中，并可选择删除它们

3 个答案: