如何滚动在Windows窗体C＃中增加图片框大小？

Question

I have a PictureBox control in windows form with a movable rectangle drawing in it, my PictureBox size will increase according to the position of the rectangle, when the PictureBox size is greater than a particular size scrollbar will appear.

public void PicBox_MouseDown(object sender, MouseEventArgs e)
{

       if (rect.Contains(new Point(e.X, e.Y)))
       {
           mMove = true;
       }

       oldX = e.X;
       oldY = e.Y;
}

 public void Picbox_MouseUp(object sender , MouseEventArgs e)
 {
      mMove = false;
 }

 public void Picbox_MouseMove(object sender,MouseEventArgs e)
 {
      if (mMove)
      {
            picBox.Cursor = Cursors.Cross;
            rect.X = rect.X + e.X - oldX;
            rect.Y = rect.Y + e.Y - oldY;
      }
      oldX = e.X;
      oldY = e.Y;
      picBox.Invalidate();
 }

public void Picbox_MousePaint(object sender, PaintEventArgs e)
{
        picBox.Invalidate();
        picBox.Size = new Size((rect.Width + rect.X) + 10, (rect.Height + rect.Y) + 10);
        Draw(e.Graphics);  
}

On first display of form with pictureBox

After dragging the rectangle the size of the pictureBox increases and scroll bar appears

everything works fine here but my problems is no matter how much the size of the pictureBox is the scroll bar works fine when i drag it down,but when the rectangle is dragged up and if the edges of the pictureBox meets the form the whole scroll bar is reset to normal, by looking at the pictures below you will be able to understand what i want to say

How to solve this, is there another way to increase scroll according to the width of pictureBox ? i am new at this.

the rectangle is acting as if the the X and Y co-ordinates are tracked with respect to winform but not pictureBox.

Can i make pictureBox as a parent for my Drawing?

Answer 1

I'm afraid this isn't possible.

In Winforms Scrollbars will only bring things back into view that have overflown their container. If they 'underflow', ie if their Top and/or Left values get negative no ScrollBars show and even if they do (because of additional overflow) they won't bring them back.

The minimum scroll position is zero .

So you will have to make sure not to move things into the negative!

You can enforce ScrollBars by adding dummy controls but that will only allow you to completely scroll the PictureBox up or left out of sight, not back!

If you really really really really really really want to you can detect the situation and manually add ScrollBar controls and code them to move the PictureBox back down/right..

Since you were asking, here is an example to play with. Note though that working with coded ScrollBars has numerous pitfalls..

• One of them would be how to handle the situation when the real ScrollBar shows up as well? In the example I solve it by not adding the ScrollBar to the Panel but by overlaying it; thus the real ScrollBar is hidden while the coded one is showing.
• Another problem are the numbers: How many pixels should the content be moved? I don't let the uses scroll anywhere but up and when that happens I move the PictureBox all the way back and the coded ScrollBar disappears..
• As a last point of warning it should be noted, that a coded ScrollBar lets you do things to the controls you have; but it won't allow you to actually scroll into the negative realm! which I guess is what you would actually like. But I think this is impossible!

So, I suggest you don't use the code below, unless you are OK with simply bringing the PictureBox.Top back to zero!

// a variable at class level:
VScrollBar vScroll = null;

// move into negative for testing:
pictureBox1.Top = -15;
// now check to see if we need a VScrollBar
scrollCheck();

void scrollCheck()
{
    if (pictureBox1.Top < 0)
    {
        if (vScroll == null )
        { vScroll = new VScrollBar(); vScroll.Parent = panel1.Parent;
        vScroll.Scroll += vScroll_Scroll; vScroll.BringToFront();
        }
        vScroll.Location = new Point(panel1.Right - vScroll.Width - 2, panel1.Top + 1);
        vScroll.Height = panel1.ClientSize.Height - 2;
        vScroll.Value = vScroll.Maximum;
        vScroll.Show();
        }
    else
    { vScroll.Hide(); }
}

void vScroll_Scroll(object sender, ScrollEventArgs e)
{
    int delta = e.NewValue - e.OldValue;
    if (delta < 0)
    {
        pictureBox1.Top = 0;
        scrollCheck();
    }
}

All in all I really believe that avoiding the situation will be best..