无法让fragmentContainer在android studio中工作

Question

我正在android studio中开发一个应用程序，其中包含一个我似乎无法开始工作的fragmentContainer。我只是得到一个错误说：

Error:(20, 53) error: cannot find symbol variable fragmentContainer

代码如下：

package criminalintent.android.bignerdranch.com.criminalintentnew;



import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;

/**
 * This is the view-class. This Class is getting with the CrimeFragment controller.
 */

public class CrimeActivity extends FragmentActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_crime);
    // Organize fragment addition to main UI :
        FragmentManager fragManager = getSupportFragmentManager();
        Fragment fragment = fragManager.findFragmentById(R.id.fragmentContainer); // this is where it starts to mention the error. 

        if (fragment == null) {
            fragment = new CrimeFragment();

            fragManager.beginTransaction().add(R.id.fragmentContainer, fragment).commit(); // also shows up as error. 
        }
    }
}

知道为什么它不起作用？ 提前致谢。