I'm trying to implement a personal way of undo/redo in a finger paint-like app.

I have in synthesis three objects: the Main class (named ScorePadActivity), the relative Main Layout (with buttons, menus, etc, as well as a View object where I create my drawings), and a third object named ArrayList where i'm writing the undo/redo code.

The problem is, when I press the undo button nothing happens, but if I draw anything again "one-time" and press undo, the screen is updated. If I draw many times, to see any changes happen on screen I have to press the undo button the same number of times I have drawn.

Seems like (as in title) when I add a bitmap to the array list the last element is duplicated in previous indexes, and for some strange reason, everytime I press the Undo Button, the system is ok for one time, but starts to duplicate until the next undo. The index increase is verified with a series of System.out.println inserted in code.

Now when I draw something on screen, the array list is updated with the code inserted after the invocation of touchup(); method in motionEvent

touch_up(); }
      this.arrayClass.incrementArray(mBitmap);
    mPath.rewind();
      invalidate();

and in ArrayList activity;

public void incrementArray(Bitmap mBitmap) {
this._mBitmap=mBitmap;
_size=undoArray.size();
    undoArray.add(_size, _mBitmap);
    }

(All Logs removed for clear reading)

The undo button in ScorePadActivity calls the undo method in View activity:

Button undobtn= (Button)findViewById(R.id.undo);
undobtn.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                mView.undo();
                }
        });

in View activity:

public void undo() {
this.mBitmap= arrayClass.undo();
 mCanvas = new Canvas(mBitmap); 
  mPath.rewind();
    invalidate();
}

that calls the relative undo method in ArrayList activity:

public Bitmap undo() {
    // TODO Auto-generated method stub
    _size=undoArray.size();
                    if (_size>1) {
    undoArray.remove(_size-1);
_size=undoArray.size();
          _mBitmap = ((Bitmap) undoArray.get(_size-1)).copy(Bitmap.Config.ARGB_8888,true);
}
return _mBitmap;
    }

return mBitmap and invalidate:

Due to my bad English I have made a scheme to make the problem more clear:

I have tried with HashMap, with a simple array, I have tried to change mPath.rewind(); with reset();, new Path(); etc but nothing. Why?

Sorry for the complex answer, i want give you a great thanks in advance. Best regards