android - Null Pointer Exception at calling postInvalidate method in thread class -

i have created custom thread , used postinvalidate method recalling , move image there null pointer exception @ thread class animthread postinvalidate .

package com.example.ahmad.ballmoving;     import android.view.view;     /**      * created ahmad on 7/30/2015.      */     public class animthread extends thread {         private view threadview;         public animthread(view view )         {             if(view!=null) {                 threadview = view;             }         }          @override         public void run()         {             while(true) {                 try {                     thread.sleep(1000);                     threadview.postinvalidate();                      } catch (interruptedexception e) {                     e.printstacktrace();                 }             }         }     } 

this custom view class .

    package com.example.ahmad.ballmoving;     import android.content.context;     import android.graphics.bitmap;     import android.graphics.bitmapfactory;     import android.graphics.canvas;     import android.graphics.color;     import android.graphics.paint;     import android.graphics.rect;     import android.util.attributeset;     import android.view.view;      /**      * created ahmad on 7/29/2015.      */     public class mycontextview extends view     {         int xvelocity=1;         int yvelocity=1;         private runnable runn;         bitmap imag1;         int x=0,y=0;          public mycontextview(context context, attributeset att)         {             super(context);   imag1=bitmapfactory.decoderesource(getresources(),r.drawable.images);         }          @override         protected void ondraw(canvas canvas) {              super.ondraw(canvas);              x=x+xvelocity;             y=y+yvelocity;            //canvas.save();             //invalidate();             canvas.drawbitmap(imag1, x, y, null);          }     } 

this main class

package com.example.ahmad.ballmoving;     import android.support.v7.app.actionbaractivity;     import android.os.bundle;     import android.view.menu;     import android.view.menuitem;     public class mainactivity extends actionbaractivity {         private thread thread1;         private thread thread2;         public mycontextview mcv;         @override         protected void oncreate(bundle savedinstancestate) {             super.oncreate(savedinstancestate);             setcontentview(r.layout.activity_main);             mycontextview c = (mycontextview)findviewbyid(r.id.ko);             thread = new animthread(c);             a.start();         }      } 

this xml of main class :

<relativelayout xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"     android:layout_height="match_parent" android:paddingleft="@dimen/activity_horizontal_margin"     android:paddingright="@dimen/activity_horizontal_margin"     android:paddingtop="@dimen/activity_vertical_margin"     android:paddingbottom="@dimen/activity_vertical_margin" tools:context=".mainactivity">      <com.example.ahmad.ballmoving.mycontextview         android:layout_height="fill_parent"         android:layout_width="fill_parent"         android:id="@+id/ko"/>   </relativelayout> 

can please try countdowntimer ?

new countdowntimer(1000,100) {          @override         public void ontick(long millisuntilfinished) {          }          @override         public void onfinish() {              threadview.postinvalidate();          }     }.start(); 

hope you.