picturebox控件共有兩種載入圖片方式，分別為：

pictureBox1.BackgroundImage = Image，pictureBox1.load(url)

為使加載的圖片自使用控件尺寸，可以分別對pictureBox控件設置BackGroundImageLayout=Stretch，SizeMode=StretchImagewinform中picturebox自適應圖片大小

做了一個示例，代碼如下，后面附完整項目源碼下載：

using System; using System.Windows.Forms; namespace HoverTreePictureBox { public partial class Form1 : Form { public Form1() { InitializeComponent(); WindowState = FormWindowState.Maximized; } private void button_getPicture_Click(object sender, EventArgs e) { pictureBox_HoverTree.SizeMode = PictureBoxSizeMode.StretchImage; pictureBox_HoverTree.BackgroundImageLayout = ImageLayout.Stretch; try { pictureBox_HoverTree.Load(""); } catch (Exception ex){ MessageBox.Show("何問起",ex.Message); } } private void button_hovertreeZoom_Click(object sender, EventArgs e) { //圖像大小按其原有的大小比例被增加或減少 by 何問起 pictureBox_HoverTree.SizeMode = PictureBoxSizeMode.Zoom; } private void button_HovertreeStretch_Click(object sender, EventArgs e) { //PictureBox 中的圖像被拉伸或收縮，以適應PictureBox的大小。 by 何問起 pictureBox_HoverTree.SizeMode = PictureBoxSizeMode.StretchImage; } private void s_Click(object sender, EventArgs e) { //調整PictureBox的大小，使其等于所包含圖像的大小 by 何問起 pictureBox_HoverTree.SizeMode = PictureBoxSizeMode.AutoSize; } } }