Question

我有一个持有图片盒的课程。我创建了一个类的对象数组，但是当我尝试创建一个新的图片框时，我收到一个错误说明，对象引用未设置为对象的实例。

以下是我创建图片框的方法

 GreyHound[] dog;

    public Form1()
    {
       InitializeComponent();
       dog[1].MyPictureBox = new PictureBox();
       dog[1].MyPictureBox = pictureBox1;

       dog[2].MyPictureBox = new PictureBox();
       dog[2].MyPictureBox = pictureBox2;

       dog[3].MyPictureBox = new PictureBox();
       dog[3].MyPictureBox = pictureBox3;

       dog[4].MyPictureBox = new PictureBox();
       dog[4].MyPictureBox = pictureBox4;

编辑代码：

GreyHound []狗;

    public Form1()
    {

       InitializeComponent();
       dog = new GreyHound[4];
       dog[0].MyPictureBox = new PictureBox();
       dog[0].MyPictureBox = pictureBox1;

       dog[1].MyPictureBox = new PictureBox();
       dog[1].MyPictureBox = pictureBox2;

       dog[2].MyPictureBox = new PictureBox();
       dog[2].MyPictureBox = pictureBox3;

       dog[3].MyPictureBox = new PictureBox();
       dog[3].MyPictureBox = pictureBox4;



    }

Answer 1

您拥有的代码有几个严重的问题：

NullReferenceException的原因有两个：
1. 您声明了一个GreyHound数组，但您从未初始化它。这意味着，dog为null并尝试访问dog[1]会导致NullReferenceException。
2. 如果你想解决这个问题，你还会遇到另一个问题：
  假设GreyHound是一个引用类型，这意味着您必须为数组中的每个项创建一个实例。使用当前代码，数组中的所有项都为null，当尝试访问数组中任何项目的属性NullReferenceException时会导致MyPictureBox，因为dog[1]会是null。
对于数组中的每个项目，您首先将PictureBox的新实例分配给属性MyPictureBox，但是使用pictureBoxX覆盖下一行中的该值。
由于我们在C＃中，数组是零索引的，因此第一项的索引为0而不是1。

修复你的代码：

GreyHound[] dog = new GreyHound[4]; // solves problem 1.1

dog[0] = new GreyHound(); // solves problem 1.2
dog[0].MyPictureBox = pictureBox1;

dog[1] = new GreyHound(); // solves problem 1.2
dog[1].MyPictureBox = pictureBox2;

dog[2] = new GreyHound(); // solves problem 1.2
dog[2].MyPictureBox = pictureBox3;

dog[3] = new GreyHound(); // solves problem 1.2
dog[3].MyPictureBox = pictureBox4;

Answer 2

您不会在任何地方初始化数组：

dog = new GreyHound[4];

数组索引也从0开始，所以：

dog[0].MyPictureBox = new PictureBox();
dog[0].MyPictureBox = pictureBox1;

dog[1].MyPictureBox = new PictureBox();
dog[1].MyPictureBox = pictureBox2;

dog[2].MyPictureBox = new PictureBox();
dog[2].MyPictureBox = pictureBox3;

dog[3].MyPictureBox = new PictureBox();
dog[3].MyPictureBox = pictureBox4;

图片框始终抛出未设置为对象错误实例的对象引用

2 个答案: