C＃PictureBox的可见属性导致false时PictureBox为null

Question

我是C＃的新手，正在尝试编写小型存储卡游戏。我有一个内部有16个图片框的TableLayouPanel，每当我使图片框不可见时（设置游戏图像时），我的事件方法都显示单击图片框时我的图片框为空。

如果我在设置游戏时保持图像可见，则事件方法将图片框视为非空。

在下面查看我的代码段：

private void AssignIconsToSquare()
{
        foreach (Control control in gameIconTable.Controls)
        {
            PictureBox picture = control as PictureBox;
            if (picture != null)
            {
                int randomNumber = random.Next(symbols.Count);
                picture.Image = symbols[randomNumber];

                symbols.RemoveAt(randomNumber);
                picture.Visible = false;

                Console.WriteLine(picture == null); // this is false here
            }


        }
}


private void pictureClick(object sender, EventArgs e)
{
        PictureBox clickedImage = sender as PictureBox;
        Console.WriteLine(clickedImage == null); // this is true here

        if (clickedImage != null)  // does not get past this line
        {
        if (clickedImage.Visible == true)
        {
              return;
        }

        if (firstSymbolClicked.Visible == false)
        { 
           firstSymbolClicked.Visible = true;
            return;
        }

       .............................