android新手关于 DialogInterface 的有关问题

//标签切换事件处理，setOnTabChangedListener
        mTabHost.setOnTabChangedListener(new OnTabChangeListener()
        {
            // TODO Auto-generated method stub
            @Override
            public void onTabChanged(String tabId)
            {
                Dialog dialog = new AlertDialog.Builder(MainActivity.this)
                        .setTitle("提示")
                        .setMessage("当前选中："+tabId+"标签")
                        .setPositiveButton("确定",
                        new DialogInterface.OnClickListener()
                        {
                            public void onClick(DialogInterface dialog, int whichButton)
                            {
                                dialog.cancel();
                            }
                        }).create();//创建按钮
               
                dialog.show();
            }