無法解析符號CrimeFragment Android Studio

Question

我得到一個不能解決CrimeFragment的符號錯誤，我不知道爲什麼。我是初學者，所以我不知道如何解決這個問題。下面是CrimeActivity.java

代碼

package com.bignerdranch.android.criminalintent; 

import android.support.v4.app.Fragment; 
import android.support.v4.app.FragmentActivity; 
import android.support.v4.app.FragmentManager; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 

public class CrimeActivity extends FragmentActivity { 

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

     FragmentManager fm = getSupportFragmentManager(); 
     Fragment fragment = fm.findFragmentById(R.id.fragment_container); 

     if (fragment == null) { 
      fragment = new CrimeFragment(); 
      fm.beginTransaction() 
        .add(R.id.fragment_container, fragment) 
        .commit(); 
     } 
    } 
} 

Answer 1

好像你不導入你的類CrimeFragment