Change canvas color onTouchEvent Android -

i'm trying make activity in canvas color changes when tap canvas.

with code have, error:

attempt invoke virtual method 'void android.graphics.canvas.drawrect(float, float, float, float, android.graphics.paint)' on null object reference

this part of activity code.

public class coloractivity extends activity  {      private float x = 0;     private float y = 0;      public canvas canvas;      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_color);          setcontentview(new myview(this));     }      public class myview extends view {          public myview(context context) {             super(context);             // todo auto-generated constructor stub             setfocusableintouchmode(true);         }          @override         protected void ondraw(canvas canvas) {              super.ondraw(canvas);             int x = getwidth();             int y = getheight();              paint paintcanvas = new paint();             paintcanvas.setstyle(paint.style.fill);             paintcanvas.setcolor(color.white);             paintcanvas.setcolor(color.parsecolor("#f44336"));             canvas.drawrect(0, 0, x, y, paintcanvas);         }          public boolean ontouchevent(motionevent event) {             switch (event.getaction()) {                 case motionevent.action_down:                      paint repaintcanvas = new paint();                     repaintcanvas.setstyle(paint.style.fill);                     repaintcanvas.setcolor(color.white);                     repaintcanvas.setcolor(color.parsecolor("#2196f3"));                     canvas.drawrect(0, 0, 100, 100, repaintcanvas);                      invalidate();                     break;                 case motionevent.action_move:                     log.d("log","move");                     invalidate();                     break;                 case motionevent.action_up:                     log.d("log", "up");                     invalidate();                     break;             }             return super.ontouchevent(event);         }       } 

what doing wrong?

i think know problem. invalidate calls again ondraw() method , overwrites whatever paint in ontouchevent method.

try following code:

public class coloractivity extends activity  {  private float x = 0; private float y = 0;  public canvas canvas;     @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_color);      setcontentview(new myview(this));   }  public class myview extends view {      paint paintcanvas;      public myview(context context) {         super(context);         paintcanvas = new paint();         paintcanvas.setstyle(paint.style.fill);         paintcanvas.setcolor(color.white);         paintcanvas.setcolor(color.parsecolor("#f44336"));         // todo auto-generated constructor stub         setfocusableintouchmode(true);     }      @override     protected void ondraw(canvas canvas) {          super.ondraw(canvas);         int x = getwidth();         int y = getheight();           canvas.drawrect(0, 0, x, y, paintcanvas);     }      public boolean ontouchevent(motionevent event) {         switch (event.getaction()) {             case motionevent.action_down:                   paintcanvas.setstyle(paint.style.fill);                 paintcanvas.setcolor(color.white);                 paintcanvas.setcolor(color.parsecolor("#2196f3"));                  invalidate();                 break;             case motionevent.action_move:                 log.d("log","move");                 invalidate();                 break;             case motionevent.action_up:                 log.d("log", "up");                 invalidate();                 break;         }         return super.ontouchevent(event);     }   }