将列表框项目传递到另一个表单C#上的文本框 [英] pass listbox item to a textbox on another form c#

问题描述

我正在用c#在Visual Studio中制作这个简单的Windows窗体应用程序.我有两种形式.在form1上，我有一个文本框，列表框和两个按钮(一个用于从文本框插入到列表框，另一个用于打开form2).在form2上，我只有一个文本框.我只是想要，当在form1上单击一个按钮(用于打开form2)时，要打开form2，文本框要包含(在formLoad上)来自form1的列表框中的选定项.但是，当我单击按钮时，它说对象引用未设置为对象的实例".我究竟做错了什么?我很确定这很简单，但我做不到.

I am making this simple Windows forms app in Visual studio in c#. I have two forms. On form1 I have a textbox,listbox and two buttons (one to insert into listbox from textbox and another to open form2). On form2 I only have a textbox. I just simply want, when click on a button (for opening form2) on form1, form2 to open and textbox to contain (on formLoad) selected item from listbox from form1. But when I click on button it says "Object reference not set to an instance of an object". What am I doing wrong? I am pretty sure it's something simple but I just can't get it.

提前谢谢！

这是我的代码:

在form1上:

  public partial class Form1 : Form
  {
    public Form1()
    {
        InitializeComponent();
    }

    private void btnOpenForm2_Click(object sender, EventArgs e)
    {
        Form2 f2 = new Form2();
        f2.ShowDialog();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        listBox1.Items.Add(textBox1.Text);
    }
    public string Transfer
    {
        get { return listBox1.SelectedItem.ToString(); }
    }

以及在form2上:

 public partial class Form2 : Form
  {
    public Form2()
    {
        InitializeComponent();
    }

    private void Form2_Load(object sender, EventArgs e)
    {
        Form1 f1 = new Form1();
        textBox1.Text = f1.Transfer;
    }

推荐答案

因为在Form2_Load事件中，您总是创建Form1的新实例，然后访问Transfer属性，该属性访问的listBox1.SelectedItem并非为新创建的表单设置.

Because in the Form2_Load event you always create a new instance of Form1 and then access the Transfer property which accesses listBox1.SelectedItem which is not set for the newly created form.

您应该在按钮事件中将裁判移交给表格1:

You should rather pass a referece to form 1 in the button event:

在form1上:

private void btnOpenForm2_Click(object sender, EventArgs e)
{
    Form2 f2 = new Form2(this);
    f2.ShowDialog();
}

以及在form2上:

public partial class Form2 : Form
{
   Form1 f1;
   public Form2(Form1 f1)
   {
       this.f1 = f1;
       InitializeComponent();
   }

   private void Form2_Load(object sender, EventArgs e)
   {
       textBox1.Text = this.f1.Transfer;
   }
}

这篇关于将列表框项目传递到另一个表单C#上的文本框的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！