关于浮动窗口怎么打包成jar

public class Mouse extends Activity{
     private WindowManager mWM;
     private ImageView ivCursor；
     private WindowManager.LayoutParams mParams;
     private int a,b;     
     @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        
    }
     public void mouse(){    
         mWM= (WindowManager) this.getBaseContext().getSystemService(Context.WINDOW_SERVICE);
         ivCursor= new ImageView(getBaseContext());
         ivCursor.setImageResource(com.example.jarmouse.R.drawable.ic_launcher);
         mParams = new WindowManager.LayoutParams();//对ivCursor对象的参数描述对象 
         mParams.height = WindowManager.LayoutParams.WRAP_CONTENT;//宽度自适应 
         mParams.width = WindowManager.LayoutParams.WRAP_CONTENT;//高度自适应 
         mParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;//设置成不能获取焦点 
         mParams.type = LayoutParams.TYPE_PHONE; 
            //设置图片格式，效果为背景透明
         mParams.format = PixelFormat.RGBA_8888;
         mParams.gravity = Gravity.LEFT | Gravity.TOP; 
         mParams.x = 0;//相对于屏幕原点的x轴距离 
         mParams.y = 0;//相对于屏幕原点的y轴距离 
         mWM.addView(ivCursor, mParams);
}

当我把这段代码打包成jar 然后去调用mouse()这个方法的时候这两个会出现空指针异常
mWM= (WindowManager) this.getBaseContext().getSystemServic(Context.WINDOW_SERVICE);
ivCursor= new ImageView(getBaseContext());
把mouse（）方法里的这段代码放到 oncreat方法中的时候就没问题
但是这样的话在引用这个jar包的程序虽然能正常运行 就是没有显示出一个浮动框