How to move back in a list with removing the last cell in the list

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Hey guys

i created a paint project with the option of Undo and Redo
After i press on the undo button i have to jump one step higher in the list
in order to be able to show the last action

the problem starts when after first click on the Undo button and then on the Redo button
then when i want to press on the undo button again it's shows me the second cell from the end and not the last

because after every press on the Undo button i Remove the last cell in the list
is there any other way to move back in the list without removing the last cell ?

C#

private void BtnUndo_Click(object sender, EventArgs e)
        {
            PicInMemory = UndoList[UndoList.Count - 1];
            PaintOnPanel = panel1.CreateGraphics();
            PaintOnPanel.DrawImage(PicInMemory, 0, 0);
            UndoList.RemoveAt(UndoList.Count - 1);         ---> the problem is with this line
            undocounter++;
        }

        private void BtnRedo_Click(object sender, EventArgs e)
        {
            PicInMemory = RedoList[RedoList.Count - undocounter];
            PaintOnPanel = panel1.CreateGraphics();
            PaintOnPanel.DrawImage(PicInMemory, 0, 0);
            undocounter--;
        }

Thank's for the help ...

Posted 2-Jun-13 21:26pm

MikeJames1987

Updated 2-Jun-13 21:33pm

CHill60

v2

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OriginalGriff · Answer 1 · 2013-06-02T21:47:00

Solution 1

Why are you removing an action from your undo list, without adding it to your redo list? And why do you not remove items from the redo list and put them on the undo list?

I suspect that you need to do both of these things, and when you do, your problem may disappear...

Posted 2-Jun-13 21:47pm

OriginalGriff

lukeer · Answer 2 · 2013-06-02T23:13:00

Solution 2

Or use a slightly different approach:

Keep just one list of operations plus the current index of the last operation.
On Undo: decrement index.
On Redo: increment index.
On Operation: Throw away what's after index in the list, append operation, increment index.

Posted 2-Jun-13 23:13pm

lukeer

MikeJames1987 · Answer 3 · 2013-06-03T01:08:00

C#

private void BtnUndo_Click(object sender, EventArgs e)
{
    Counter++; 
    PicInMemory = UndoList[UndoList.Count - Counter]; 
    PaintOnPanel = panel1.CreateGraphics();
    PaintOnPanel.DrawImage(PicInMemory, 0, 0);
    UndoMade = true;
    BtnRedo.Enabled = true;
}

private void BtnRedo_Click(object sender, EventArgs e)
{
    PicInMemory = RedoList[RedoList.Count - Counter];
    PaintOnPanel = panel1.CreateGraphics();
    PaintOnPanel.DrawImage(PicInMemory, 0, 0);
    Counter--;
}