为什么在Android中从一个片段移动到另一个片段时会发生强制关闭？

我试图从一个片段移动，即点击一个按钮，mycontacts extends片段移动到另一个片段friendfragment extends片段。我得到的错误类似于

找不到片段的视图

。我的代码和错误日志如下。请引导我，因为我是一个碎片新手

tasks.xml文件

<?xml version="1.0" encoding="utf-8"?>
    <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
      android:layout_width="match_parent"
      android:id="@+id/tasky"
      android:layout_height="match_parent"
      android:orientation="vertical" >


  <fragment
    android:id="@+id/fragment1"
    android:name="com.example.taskmanager.friendfragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

  <Button
   android:id="@+id/button1"
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:text="Button" />

 </FrameLayout>

friendfragment.class

 public class friendfragment extends Fragment {
public friendfragment() {

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {


    View view = inflater.inflate(R.layout.tasks, container,
            false);
    return view;
}
}

tasks.xml

 <?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:id="@+id/tasky"
android:layout_height="match_parent"
android:orientation="vertical" >



 <fragment
    android:id="@+id/fragment1"
    android:name="com.example.taskmanager.friendfragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button" />

任务：

碎片活动：

 Fragment fr = new friendfragment();
 FragmentManager fm=getFragmentManager();
 FragmentTransaction ft=fm.beginTransaction();
 ft.replace(R.id.fragment_content, fr).commit();

04-23 15:00:21.074: E/Trace(26708): error opening trace file: No such file or directory (2)
04-23 15:00:47.933: E/FragmentManager(26708): No view found for id 0x7f040051 (com.example.taskmanager:id/fragment1) for fragment friendfragment{40e187b8 #1 id=0x7f040051}
04-23 15:00:47.933: E/FragmentManager(26708): Activity state:
04-23 15:00:47.963: E/FragmentManager(26708):   Local Activity 40cd4eb8 State:
04-23 15:00:47.973: E/FragmentManager(26708):     mResumed=true mStopped=false mFinished=false
04-23 15:00:47.995: E/FragmentManager(26708):     mLoadersStarted=true
04-23 15:00:47.995: E/FragmentManager(26708):     mChangingConfigurations=false
04-23 15:00:48.003: E/FragmentManager(26708):     mCurrentConfig={1.0 310mcc260mnc en_US ldltr sw320dp w320dp h455dp 160dpi nrml port finger qwerty/v/v -nav/h s.6}

<?xml version="1.0" encoding="utf-8"?>
    <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
      android:layout_width="match_parent"
      android:id="@+id/frame_content"
      android:layout_height="match_parent"
      android:orientation="vertical" >

 </FrameLayout>

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

     <!-- Your views here -->

 </RelativeLayout>

   public class friendfragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {


        View view = inflater.inflate(R.layout.fragment_friend, container,
                false);
        return view;
    }
   }

 Fragment fr = new friendfragment();
 FragmentManager fm=getFragmentManager();
 FragmentTransaction ft=fm.beginTransaction();
 ft.replace(R.id.fragment_content, fr).commit();