i'm working on project create mirror of drawing. main logic working fine.only thing causing problem redo , undo functionality. have searched lot. implement may methods couldn't success. following drawing class.
drawingview.java
private arraylist<path> paths = new arraylist<path>(); private arraylist<path> undonepaths = new arraylist<path>(); public drawingview(context context, attributeset attrs){ super(context, attrs); this.context=context; setupdrawing(); } //setup drawing private void setupdrawing(){ //prepare drawing , setup paint stroke properties brushsize = getresources().getinteger(r.integer.small_size); lastbrushsize = brushsize; drawpath = new path(); drawpath1 = new path(); drawpaint = new paint(); drawpaint.setcolor(paintcolor); drawpaint.setantialias(true); drawpaint.setstrokewidth(brushsize); drawpaint.setstyle(paint.style.stroke); drawpaint.setstrokejoin(paint.join.round); drawpaint.setstrokecap(paint.cap.round); canvaspaint = new paint(paint.dither_flag); } //size assigned view @override protected void onsizechanged(int w, int h, int oldw, int oldh) { super.onsizechanged(w, h, oldw, oldh); canvasbitmap = bitmap.createbitmap(w, h, bitmap.config.argb_8888); width=w; height=h; log.d("width,height", w + " , " + h); drawcanvas = new canvas(canvasbitmap); } //draw view - called after touch event @override protected void ondraw(canvas canvas) { (path p : paths){canvas.drawpath(p, drawpaint);} canvas.drawpath(drawpath, drawpaint); log.i("ondrawing", "reach on draw"); /*canvas.drawbitmap(canvasbitmap, 0, 0, canvaspaint); canvas.drawpath(drawpath, drawpaint); canvas.drawpath(drawpath1, drawpaint);*/ } //register user touches drawing action @override public boolean ontouchevent(motionevent event) { float touchx = event.getx(); float touchy = event.gety(); //respond down, move , events switch (event.getaction()) { case motionevent.action_down: drawpath.reset(); undonepaths.clear(); drawpath.moveto(touchx, touchy); undonepaths.clear(); break; case motionevent.action_move: drawpath.lineto(touchx, touchy); break; case motionevent.action_up: drawpath.lineto(touchx, touchy); drawcanvas.drawpath(drawpath, drawpaint);// commit path our offscreen paths.add(drawpath); drawcanvas.drawpath(drawpath, drawpaint); drawpath.reset(); drawcanvas.drawpath(drawpath1, drawpaint); drawpath1.reset(); break; default: return false; } //redraw invalidate(); return true; } what missing here? suggestions/ideas/examples best way implement kind of functionality on project?
canvas drawing sort of hierarchal in drawing happens in order them.
so drawing should done in ondraw , here.
your draw events should pushed on draw stack. not store canvas. store operations supposed happen when drawing occurs (coordinates, width, , color of path example).
an "undo" operation can done popping drawing stack , pushing event "redo" stack. "redo" event can done popping "redo" stack , pushing on "drawing" stack.
in ondraw method of view, scan through drawing events , draw on canvas.
edit:
the ondraw() method iterate through drawing operations. first have interface called drawevent so:
public interface drawevent { void draw(canvas c); } then in view class have collection of drawevents , iterate through them in ondraw(canvas c).
public class myview extends view { deque<drawevent> drawevents = new linkedlist<drawevent>(); @override public void ondraw(canvas c) { (drawevent e : drawevents) { e.draw(c); } } } 
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