創建CallbackManager.Factory.create（）的實例;

Question

當我寫這段代碼爲什麼mFacebookCallbackManager的顏色變爲紅色說法無法解析符號mFacebookCallbackManager

public class signin extends AppCompatActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    FacebookSdk.sdkInitialize(getApplicationContext()); 
    mFacebookCallbackManager = CallbackManager.Factory.create(); 


    setContentView(R.layout.activity_signin); 

} 

} 

清單文件

<application 
    android:allowBackup="true" 
    android:icon="@mipmap/ic_launcher" 
    android:label="@string/app_name" 
    android:roundIcon="@mipmap/ic_launcher_round" 
    android:supportsRtl="true" 
    android:theme="@style/AppTheme"> 

    <meta-data android:name="com.facebook.sdk.ApplicationId" android:value="@string/facebook_app_id"/> 

    <activity 
     android:name=".MainActivity" 
     android:label="@string/app_name" 
     android:theme="@style/AppTheme.NoActionBar"> 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 
</application> 

</manifest> 

請幫我解決這個問題

Answer 1

你做不聲明變量mFacebookCallbackManager。