nullpointerexception - Android Canvas drawcolor throws Null pointer exception -

developing small android game (2.1 till 4.2 support), below code throws java.lang.nullpointerexception exception at

canvas.drawcolor((0xffaaaaaa);

public class maingamepanel extends surfaceview implements surfaceholder.callback {  public void render(canvas canvas) {                       canvas.drawcolor(0xffaaaaaa);             droid.draw(canvas);      } } 

here stack trace

java.lang.nullpointerexception @ com.rdx.play.maingamepanel.render(maingamepanel.java:186) @ com.rdx.play.mainthread.run(mainthread.java:54) 

the exception inconsistent, might causing issue?

many thanks.

surfaceholder.lockcanvas() allowed return null (cos thread doesn't have same lifetime surface). bet aren't handling possibility in thread function.