Thread: Issues with undo functions

I'm trying to make a redo feature for my app, but I can't figure out what is wrong :/ The idea is to be able to undo up to 10 times, and each time you make a new modification to the image (when you pick you finger up to stop drawing) it shifts all previous images one index to make room for the newest edit and then it saves the edit in the last index of an array of bitmaps. for now I'm just drawing the 3 most recent bitmaps to see if it is working, but all the saved bitmaps are the same. Could I get some advice? Thanks!

float lastPosX;
float lastPosY;
Bitmap[] previousEdits = new Bitmap[10]
 public MyView(Context c) {
            super(c);
            mBitmap = Bitmap.createBitmap(screenWidth, screenHeight, Bitmap.Config.ARGB_8888);
            mCanvas = new Canvas(mBitmap);
            currentPath = new Path();
            mBitmapPaint = new Paint(Paint.DITHER_FLAG);
            for(int i=0;i<previousEdits.length;i++){  //initialize all 10 steps previous edits to be blank bitmaps instead of null
    	        previousEdits[i]=Bitmap.createBitmap(screenWidth, screenHeight, Bitmap.Config.ARGB_8888);
        	}
        }
 
protected void onDraw(Canvas canvas) {
                canvas.drawColor(Color.WHITE);
            	canvas.drawBitmap(previousEdits[previousEdits.length-1], 0, 0, mBitmapPaint);  //draw the most current image
            	canvas.drawBitmap(previousEdits[previousEdits.length-2], 500, 0, mBitmapPaint); //draw second most current 
            	canvas.drawBitmap(previousEdits[previousEdits.length-3], 500, 0, mBitmapPaint); //draw third most current
        }
 public boolean onTouchEvent(MotionEvent event) {
                  float x = event.getX();
                  float y = event.getY();
                 switch (event.getAction()) {
                   case MotionEvent.ACTION_DOWN:
                           touch_start(x, y);
                            invalidate();
                            break;
                    case MotionEvent.ACTION_MOVE:
                            touch_move(x, y);
                           invalidate();
                            break;
                     case MotionEvent.ACTION_UP:
                            touch_up();
                           invalidate();
                            break;
             }
               return true;
        }
 private void touch_start(float x, float y) {
            currentPath.moveTo(x, y);
            lastPosX = x;
            lastPosY = y;
        }
private void touch_move(float x, float y) {
            float dx = Math.abs(x - lastPosX);
            float dy = Math.abs(y - lastPosY);
                currentPath.quadTo(lastPosX, lastPosY, (x + lastPosX)/2, (y + lastPosY)/2);
            	lastPosX = x;
                lastPosY = y;        
        }
private void touch_up() {
        	 // commit the path to our offscreen
        	if(canvasInUse) {
        		mCanvas.drawPath(currentPath, drawingPaint);
        	}
            // kill this so we don't double draw
            currentPath.reset();
           //update the previous bitmaps
            updateLatestEdits(mBitmap);
        }
 
void updateLatestEdits(Bitmap latestEdit){    	
    		for(int i =0;i<previousEdits.length-1;i++){ //shift bitmaps to make room for new edit
    			previousEdits[i]=previousEdits[i+1];
    		}
    		previousEdits[previousEdits.length-1]=latestEdit; //put in new edit at the end
    	}

From the look of it the only Bitmap instance you add to the array is mBitmap so it ends up occupying every slot in the array. (Or, to speak more correctly, a reference to that bitmap occupies every slot.)

that makes sense... man I'm slipping. So if I wanted to put an actual unique bitmap in each slot in the array rather than only the reference, what should I do? something like
previousEdits[previousEdits.length-1]=Bitmap.createBitmap(mBitmap); //?
Like this?

--- Update ---

Solved it!!
Instead of having the last line of the updateLatestEdits method be
previousEdits[previousEdits.length-1]=latestEdit;
I changed it to
previousEdits[previousEdits.length-1]=latestEdit.copy(Bitmap.Config.ARGB_8888, true);
So now each slot in the array has it's own unique bitmap, instead of all having the references to one. Thanks!!

Try it and see. But from the sound of the name createBitmap() is good: you are still dealing with a reference but now it's a reference to a newly created bitmap.

If mBitmap is not being used as an instance variable you could remove it.

---

[edit] Just saw the update. Copy also sounds good. I'm glad you've got it sorted out.