WinForms:图片框初始化问题

Question

如果我将PictureBox初始化放入表单的构造函数或form.Load/form.Shown处理程序中，则PictureBox上不会绘制任何内容。如果在绘制之前进行初始化，则会显示图形。

为什么此代码在 PictureBox 上绘制一个数组：

public partial class Form1 : Form
{
    Bitmap drawArea;
    public Form1()
    {
        InitializeComponent();
    }
    private void drawArray(int[] arr, PictureBox box)
    {
        //=========== Attention to this code ================
        drawArea = new Bitmap(pictureBox1.Size.Width, pictureBox1.Size.Height);
        pictureBox1.Image = drawArea;
        //===================================================
        using (Graphics g = Graphics.FromImage(drawArea))
        {
            Pen mypen = new Pen(Brushes.Black);
            g.Clear(Color.White);
            for (int i = 0; i < arr.Length; i++)
                g.DrawLine(mypen, i*2, drawArea.Height,
                   i*2, drawArea.Height - arr[i]);
        }
    }
    private void button1_Click(object sender, EventArgs e)
    {
        int[] ar1 = randomArray(20, 1, 20);
        drawArray(ar1, pictureBox1);
    }
}

但是这段代码没有？

public partial class Form1 : Form
{
    Bitmap drawArea;
    public Form1()
    {
        InitializeComponent();
        //=========== Attention to this code ================
        //Breakpoint here: pictureBox1.Size.Width==409, pictureBox1.Size.Height==205
        drawArea = new Bitmap(pictureBox1.Size.Width, pictureBox1.Size.Height);
        pictureBox1.Image = drawArea;
        //===================================================
    }
    private void drawArray(int[] arr, PictureBox box)
    {
        using (Graphics g = Graphics.FromImage(drawArea))
        {
            Pen mypen = new Pen(Brushes.Black);
            g.Clear(Color.White);
            for (int i = 0; i < arr.Length; i++)
                g.DrawLine(mypen, i*2, drawArea.Height,
                  i*2, drawArea.Height - arr[i]);
        }
    }
    private void button1_Click(object sender, EventArgs e)
    {
        int[] ar1 = randomArray(20, 1, 20);
        drawArray(ar1, pictureBox1);
    }
}

如果我制作第二个按钮并将初始化代码放入其处理程序中（当然，在单击第一个按钮之前单击第二个按钮），它甚至不起作用。

不会引发任何异常。

Answer 1

不确定...只是 Invalidate（） drawArray（） 中的 PictureBox，所以它会自行刷新：

    private void drawArray(int[] arr, PictureBox box)
    {
        using (Graphics g = Graphics.FromImage(drawArea))
        {
            Pen mypen = new Pen(Brushes.Black);
            g.Clear(Color.White);
            for (int i = 0; i < arr.Length; i++)
                g.DrawLine(mypen, i * 2, drawArea.Height,
                  i * 2, drawArea.Height - arr[i]);
        }
        box.Invalidate();
    }

*如果你不使用它，你为什么要通过图片框？