錯誤：無法找到符號變量adView

Question

當我運行它時，它表示無法解析adView。但是我輸入了它。爲什麼是這樣？

Nessecary MainActivity.Java：

package stephenshettler.apps.com.coinflip; 

import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.View; 
import android.view.animation.AccelerateInterpolator; 
import android.view.animation.AlphaAnimation; 
import android.view.animation.Animation; 
import android.view.animation.DecelerateInterpolator; 
import android.widget.Button; 
import android.widget.ImageView; 
import com.google.android.gms.ads.AdRequest; 
import com.google.android.gms.ads.MobileAds; 
import com.google.android.gms.ads.AdView; 

import java.util.Random; 

public class MainActivity extends AppCompatActivity { 

private AdView mAdView; 

public static final Random RANDOM = new Random(); 
private ImageView coin; 
private Button btn; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    // Sample AdMob app ID: ca-app-pub-3940256099942544~3347511713 
    MobileAds.initialize(this, "ca-app-pub-8269050231653041~4290758413"); 


    mAdView = (AdView) findViewById(R.id.adView); 
    AdRequest adRequest = new AdRequest.Builder().build(); 
    mAdView.loadAd(adRequest); 

    coin = (ImageView) findViewById(R.id.coin); 
    btn = (Button) findViewById(R.id.btn); 
    btn.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 
      flipCoin(); 
     } 
    }); 


} 

在我的應用程序gradle這個，我編譯 'com.google.android.gms：發揮服務的廣告：10.2.4'

非常感謝！

Answer 1

我剛剛解決了這個問題！我不小心大寫了我的橫幅廣告ID，所以它是@ id/AdView而不是@id/adView