VB.NET中如何在PictureBox左键释放时清除_onPaint绘制的区域？

很简单，你只需要在鼠标左键释放的事件里重置绘制的矩形区域，然后刷新PictureBox就能让蓝色标记消失了。

修改步骤： #

• 找到pictureBox1_MouseUp方法，添加左键释放的处理逻辑：当检测到左键松开时，把Rect重置为一个空的Rectangle，然后调用Invalidate()触发重绘，这样Paint事件就不会再绘制这个矩形了。

修改后的完整代码： #

private Point RectStartPoint;
private Rectangle Rect = new Rectangle();
private Brush selectionBrush = new SolidBrush(Color.FromArgb(128, 72, 145, 220));

// Start Rectangle
private void pictureBox1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
{
    // Determine the initial rectangle coordinates...
    RectStartPoint = e.Location;
    Invalidate();
}

// Draw Rectangle
private void pictureBox1_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
{
    if (e.Button != MouseButtons.Left) return;
    Point tempEndPoint = e.Location;
    Rect.Location = new Point(
        Math.Min(RectStartPoint.X, tempEndPoint.X),
        Math.Min(RectStartPoint.Y, tempEndPoint.Y));
    Rect.Size = new Size(
        Math.Abs(RectStartPoint.X - tempEndPoint.X),
        Math.Abs(RectStartPoint.Y - tempEndPoint.Y));
    pictureBox1.Invalidate();
}

// Draw Area
private void pictureBox1_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{
    // Draw the rectangle...
    if (pictureBox1.Image != null)
    {
        if (Rect != null && Rect.Width > 0 && Rect.Height > 0)
        {
            e.Graphics.FillRectangle(selectionBrush, Rect);
        }
    }
}

private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        // 重置矩形为空，触发重绘后就不再显示标记
        Rect = new Rectangle();
        pictureBox1.Invalidate();
    }
    else if (e.Button == MouseButtons.Right)
    {
        if (Rect.Contains(e.Location))
        {
            Debug.WriteLine("Right click");
        }
    }
}

额外优化（可选）： #

如果你希望放入新图片时也自动清除矩形，可以在设置pictureBox1.Image的地方添加一行重置代码，比如：

// 假设你是这样设置新图片的
pictureBox1.Image = new Bitmap("新图片路径");
Rect = new Rectangle();
pictureBox1.Invalidate();

这样无论左键释放还是更换图片，蓝色标记都会消失啦！

内容的提问来源于stack exchange，提问作者Petr Klíč