InputBox NullReferenceException

Question

我创建了一个用作InputBox的表单

    public partial class InputBox : Form
    {
       public string sample
       {
          get
          { return TextBox1.Text; }
          set
          { TextBox1.Text = value; }
       }

       public InputBox(string title, string question)
       {
          this.Text = title;
          Label1.Text = question;
          InitializeComponent();
       }
    }

在我的另一种形式中，我称之为这个表格：

    private void Button1_Click(object sender, EventArgs e)
    {
        InputBox dlg = new InputBox("TITLE", "Sample Question ?");
        dlg.ShowDialog();

        if (dlg.DialogResult == DialogResult.OK)
        {
            TextBox1.Text = dlg.sample;
        }
    }

为什么我有NullReferenceException？Object reference not set to an instance of an object.

Answer 1

如下所示

public InputBox(string title, string question)
{
    InitializeComponent();
    this.Text = title;
    Label1.Text = question;
}

首先初始化组件，然后可以设置属性