Android Bitmap Undo Redo Effect

Question

Create Canvas with multiple tools like Pencil,eraser,Line,oval,triangle,square ,undo,redo etc.

Undo,Redo not working.

  @Override
        protected void onSizeChanged(int w, int h, int oldw, int oldh) {
            super.onSizeChanged(w, h, oldw, oldh);

            mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
            mCanvas = new Canvas(mBitmap);

}

score 1 · Accepted Answer · answered May 10 '16 at 06:03

1

I disagree with the first answer, store a bitmap is very expensive.

what you should store is action itself.you can create a new class call Action, and store the drawing path, Paint style,etc.and when user click the redo button, perform the action on the bitmap.

I wrote a demo about paintboard, it currently support only undo action,but with the actions store in a List,you can easily add redo feature to it.the address is PaintView.

answered May 10 '16 at 06:03

7heaven

797
7
16

Yes, store bitmap is expensive but sometimes is more simple if actions is complex – Konstantin May 10 '16 at 06:47

score -1 · Answer 2 · answered May 10 '16 at 05:37

-1

One of variants of using undo - redo is store bitmap after each action (for example using HashMap), and then replace current bitmap to preview bitmap (if is undo action) or next bitmap (if this redo action). As I know android sdk not have default api to do what you want.

answered May 10 '16 at 05:37

Konstantin

174
7

Give me sample Demo please. – Tech May 10 '16 at 06:23
Keeping a HashMap of Bitmaps for each operation is going to give you an OutOfMemoryError very quickly. – Kane O'Riley May 10 '16 at 10:28
Yes, all know it. But if you using this technology in a clever, for example not store multiple Bitmaps, and may be store some on ssd, It will not happen. – Konstantin May 10 '16 at 10:34

Android Bitmap Undo Redo Effect

2 Answers2