為什么用此代碼顯示黑屏？

Question

我正在關注Big nerd Ranch的android圖書（第二版）。 以下代碼有望顯示從CrimeLab類生成的模型數據列表（100個犯罪，每個犯罪帶有標題，日期和已解決的復選框）。在CrimeListFragment中使用recyclerView來顯示數據。 但是在構建和運行應用程序時，我得到的只是一個空白的空白屏幕。 以下是相關代碼：

public class CrimeListActivity extends FragmentActivity {

public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_fragment_host);

    FragmentManager fm = getSupportFragmentManager();
    Fragment fragment = fm.findFragmentById(R.id.fragment_container);
    if (fragment == null) {
        fragment = new CrimeListFragment();
        fm.beginTransaction().add(R.id.fragment_container, fragment).commit();
    }
}}

CrimeListFragment.java

public class CrimeListFragment extends Fragment {

private RecyclerView mCrimeRecyclerView;

private CrimeAdapter mAdapter;

public View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
    View view = inflater.inflate(R.layout.fragment_crime_list,container,false);
    mCrimeRecyclerView = (RecyclerView) view.findViewById(R.id.crime_recycler_view);
    mCrimeRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
    updateUI();
    return view;
}

private void updateUI(){
    CrimeLab crimeLab = CrimeLab.get(getActivity());
    List<Crime> crimes = crimeLab.getCrimes();
    mAdapter = new CrimeAdapter(crimes);
    mCrimeRecyclerView.setAdapter(mAdapter);

}

public class CrimeHolder extends RecyclerView.ViewHolder{

    public TextView mTitleTextView;
    private TextView mTitleTextView;
    private TextView mDateTextView;
    private CheckBox mSolvedCheckBox;
    private Crime mCrime;

    public CrimeHolder (View itemView){
        super(itemView);
      //  mTitleTextView = (TextView) itemView;
        mTitleTextView =(TextView) itemView.findViewById(R.id.list_item_crime_title_text_view);
        mDateTextView =(TextView) itemView.findViewById(R.id.list_item_crime_date_text_view);
        mSolvedCheckBox = (CheckBox) itemView.findViewById(R.id.list_item_crime_solved_check_box);
    }

    public void bindCrime(Crime crime){
        mCrime = crime ;
        mTitleTextView.setText(mCrime.getTitle());
        mDateTextView.setText(mCrime.getDate().toString());
        mSolvedCheckBox.setEnabled(mCrime.isSolved());
    }

}

public class CrimeAdapter extends RecyclerView.Adapter<CrimeHolder>{
    private List<Crime> mCrimes;

    public CrimeAdapter(List<Crime> crimes){
        mCrimes = crimes;
    }

    @Override
    public CrimeHolder onCreateViewHolder(ViewGroup parent, int viewType){
        LayoutInflater layoutInflater = LayoutInflater.from(getActivity());
        View view = layoutInflater.inflate(R.layout.list_item_crime,parent,false);
        return new CrimeHolder(view) ;
    }

    @Override
    public void onBindViewHolder(CrimeHolder holder,int position){
        Crime crime = mCrimes.get(position);
        holder.bindCrime(crime);
    }

    @Override
    public int getItemCount(){
        return mCrimes.size();
    }
}

以防萬一，CrimeLab.java ：（提供模型數據）

public class CrimeLab {
private static CrimeLab sCrimeLab;
private List<Crime> mCrimes;

public static CrimeLab get(Context context){
    if (sCrimeLab==null){
        sCrimeLab = new CrimeLab(context); //Hence calling the private constructor that no other class can access
    }
    return  sCrimeLab;
}

private CrimeLab(Context context){
    mCrimes = new ArrayList<>();
    for (int i=0; i<100; i++){
        Crime crime = new Crime();
        crime.setTitle("Crime #"+i);
        crime.setSolved(i%2==0);
        mCrimes.add(crime);
    }
}

public List<Crime> getCrimes(){
    return mCrimes;
}

content_fragment_host.xml（這是由activity_fragment_host.xml編輯的，我從其中刪除了默認的AppBarLayout＆Toolbar代碼，如果有幫助的話）

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"

tools:context="com.bignerdranch.android.crimeintent.CrimeListActivity"
tools:showIn="@layout/activity_fragment_host"
android:id="@+id/fragment_container">

</FrameLayout>

fragment_crime_list.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.RecyclerView     xmlns:android="http://schemas.android.com/apk/res/android"
                                    android:layout_width="match_parent"
                                    android:layout_height="match_parent"
                                    android:id="@+id/crime_recycler_view">

</android.support.v7.widget.RecyclerView>

list_item_crime.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            xmlns:tools="http://schemas.android.com/tools">


<CheckBox
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/list_item_crime_solved_check_box"
    android:layout_alignParentRight="true"
    android:padding="4dp"/>

<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/list_item_crime_title_text_view"
    android:layout_toLeftOf="@+id/list_item_crime_solved_check_box"
    android:textStyle="bold"
    android:padding="4dp"
    tools:text="Title"/>

<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/list_item_crime_date_text_view"
    android:layout_toLeftOf="@+id/list_item_crime_solved_check_box"
    android:layout_below="@id/list_item_crime_title_text_view"
    android:padding="4dp"
    tools:text="Date"/>

</RelativeLayout>

Answer 1

這只是一個錯字。 在CrimeListFragment.java中，onCreateView更改為OnCreateView。 但是無論如何，謝謝，這讓我發瘋。

Answer 2

每次您使用片段並想要顯示它或替換為另一個片段時，都需要從FragmentManager調用commit（）。 你的情況是fm.commit（）;

FragmentManager fm = getSupportFragmentManager();
Fragment fragment = fm.findFragmentById(R.id.fragment_container);
if (fragment == null) {
    fragment = new CrimeListFragment();
    fm.beginTransaction().add(R.id.fragment_container, fragment).commit();
}
fm.commit();