Android开发中，我现在在写一个类似win8的假界面，当作练习，我想实现整个桌面屏幕背景图片每隔一段时间就自动切换一张，我现在的代码是这样的，但实现不了，请各位大神指教。
  /*
     * 背景切换类
     */
    public class ChangeBackgroundThread extends Thread{
        @Override
        public void run() {
            // TODO Auto-generated method stub
            super.run();
            int i=0;
            do{
                try {
                    Thread.sleep(10000);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                System.out.println("----> 切换");
                main_linear.setBackgroundDrawable
                (getResources().getDrawable(BackGroundDrawable.slideImage[i]));
               
                i++;
                if(i>BackGroundDrawable.slideImage.length){
                    i=0;
                }
            }while(i<=BackGroundDrawable.slideImage.length&& mclockThread.interrupted()==false);
        }
        
    }

public class BackGroundDrawable {
   
    public static int slideImage[]={
        R.drawable.main_background,
        R.drawable.backround1,
        R.drawable.background2,
        R.drawable.background3,
        R.drawable.background4,
        R.drawable.background5,
        R.drawable.background6,
        R.drawable.background7,
        R.drawable.background8,
        R.drawable.background9,
        R.drawable.background10,
        R.drawable.background12,
        R.drawable.background13,
        R.drawable.background16,
        R.drawable.background17,
        R.drawable.background18
    };
}
为什么会实现不了呢，调试的时候，根本就执行不了main_linear.setBackgroundDrawable
                (getResources().getDrawable(BackGroundDrawable.slideImage[i]));这句

你的R是什么类或者什么接口呀
main_linear也没有声明就直接用了