Android后退事件处理

    public long lastClickTime = 0;
    public void onBackPressed(){  
     if(lastClickTime <= 0){
         Toast.makeText(this, "再按一次退出程序", 1).show();
         lastClickTime = System.currentTimeMillis();//记录当前时间
     }else{
         long currentClickTime = System.currentTimeMillis();//记录当前时间
         if(currentClickTime-lastClickTime <= 1000){ //时间差小于1000毫秒
             finish(); //退出
         }else{
             Toast.makeText(this, "再按一次退出程序", 1).show();
             lastClickTime = currentClickTime; //刷新时间
         } 
     }
   }