设计Windows应用程序：利用PictureBox控件设计一个图片查看器,观看图片及图片放大、缩小，还原比例的效果并显示代码

以下是一个简单的C#代码示例，可以通过PictureBox控件实现图片的查看、缩放、还原功能：

public partial class Form1 : Form
{
    private Image originalImage;
    private float zoomFactor = 1.0f;

    public Form1()
    {
        InitializeComponent();
    }

    private void openToolStripMenuItem_Click(object sender, EventArgs e)
    {
        OpenFileDialog openFileDialog = new OpenFileDialog();
        openFileDialog.Filter = "Image Files (*.bmp;*.jpg;*.jpeg,*.png)|*.BMP;*.JPG;*.JPEG;*.PNG";
        if (openFileDialog.ShowDialog() == DialogResult.OK)
        {
            originalImage = Image.FromFile(openFileDialog.FileName);
            pictureBox1.Image = originalImage;
            pictureBox1.SizeMode = PictureBoxSizeMode.Zoom;
            zoomFactor = 1.0f;
        }
    }

    private void zoomInToolStripMenuItem_Click(object sender, EventArgs e)
    {
        zoomFactor += 0.1f;
        pictureBox1.Width = (int)(originalImage.Width * zoomFactor);
        pictureBox1.Height = (int)(originalImage.Height * zoomFactor);
    }

    private void zoomOutToolStripMenuItem_Click(object sender, EventArgs e)
    {
        zoomFactor -= 0.1f;
        pictureBox1.Width = (int)(originalImage.Width * zoomFactor);
        pictureBox1.Height = (int)(originalImage.Height * zoomFactor);
    }

    private void actualSizeToolStripMenuItem_Click(object sender, EventArgs e)
    {
        zoomFactor = 1.0f;
        pictureBox1.Width = originalImage.Width;
        pictureBox1.Height = originalImage.Height;
    }
}

在这个示例中，我们使用了一个OpenFileDialog控件来打开图像文件，将打开的图像文件赋值给PictureBox控件的Image属性，通过设置SizeMode为Zoom来自适应显示图片，实现了缩放功能。同时，我们还为菜单栏的缩放功能提供了事件处理程序，以及还原功能。由于PictureBox控件的Width和Height属性的值为整型，因此我们需要将缩放比例转换为浮点型，并将缩放后的值进行取整。