How to implemement undo features in painting application in Android?

Question

i want to do undo features in in my application.. for this i searched i net found that take arraylist of x,y points which i have done below code i am unable for undo the drawing

Answer 1

private Slate mSlate;
private TiledBitmapCanvas mTiledCanvas;

 public void clickUndo(View unused) {

        mSlate.undo();
    }


public void undo() {
        if (mTiledCanvas == null) {
            Log.v(TAG, "undo before mTiledCanvas inited");
        }
        mTiledCanvas.step(-1);

        invalidate();
    }