我有一个flutter的ElevatedButton来显示rewardedAd，它一开始显示string:'show ad'，但是看完广告后，我想在里面显示int:'+10'，而且我想每次点击它（看广告）时增加+10。
我的代码：

RewardedAd? _rewardedAd;
      int _rewardedScore = 0;
    
      @override
      void initState() {
        // TODO: implement initState
        super.initState();
    
        _createRewardedAd();
      }
    
      void _createRewardedAd() {
        RewardedAd.load(
          adUnitId: 'ca-app-pub-3940256099942544/5224354917',
          request: AdRequest(),
          rewardedAdLoadCallback: RewardedAdLoadCallback(
            onAdLoaded: (RewardedAd ad) {
              print('$ad loaded.');
              // Keep a reference to the ad so you can show it later.
              setState(() => this._rewardedAd = ad);
            },
            onAdFailedToLoad: (LoadAdError error) {
              print('RewardedAd failed to load: $error');
              setState(() {
                _rewardedAd = null;
              });
            },
          ),
        );
      }
    
      void _showRewardedAd() {
        _rewardedAd?.fullScreenContentCallback = FullScreenContentCallback(
          onAdShowedFullScreenContent: (RewardedAd ad) =>
              print('$ad onAdShowedFullScreenContent.'),
          onAdDismissedFullScreenContent: (RewardedAd ad) {
            print('$ad onAdDismissedFullScreenContent.');
            ad.dispose(); // dispose ad and
            _createRewardedAd(); // then, create a new one
          },
          onAdFailedToShowFullScreenContent: (RewardedAd ad, AdError error) {
            print('$ad onAdFailedToShowFullScreenContent: $error');
            ad.dispose(); // dispose ad and
            _createRewardedAd(); // then, create a new one
          },
          onAdImpression: (RewardedAd ad) => print('$ad impression occurred.'),
        );
    
        _rewardedAd?.show(
            onUserEarnedReward: (AdWithoutView ad, RewardItem reward) {
          setState(() {
            _rewardedScore = _rewardedScore + 10;
    
          });
        });
    
        _rewardedAd = null;
      }

Scaffold(
      appBar: AppBar(
        title: Text('Rewarded:  $_rewardedScore'),
        centerTitle: true,
      ),
      body: Center(
        child: ElevatedButton(
          child: Text(
            "show ad",
            style: TextStyle(fontSize: 30),
          ),
          onPressed: () {
            print('clicked rewarded');
            _showRewardedAd();
          },
        ),
      ),
    );

第一节第一节第一节第一节第一次