Android 使用sqlite db将活动更改为片段

我最近尝试将一个正在工作的sqlite填充的listview活动更改为一个片段。我已经做了必要的更改，但是我仍然会遇到一些我不理解的错误。如果你们中有人能帮忙的话，这将缓解严重的挫折感

这是我的主要活动

public class FoursFragment extends Fragment {

private DbHelper mHelper;
private SQLiteDatabase dataBase;

private ArrayList<String> userId = new ArrayList<String>();
private ArrayList<String> user_fName = new ArrayList<String>();
private ArrayList<String> user_lName = new ArrayList<String>();

private ListView userList;
private AlertDialog.Builder build;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.display_activity, container, false);

    userList = (ListView) view.findViewById(R.id.List);

    mHelper = new DbHelper(getActivity());

    //add new record
    getView().findViewById(R.id.btnAdd).setOnClickListener(new OnClickListener() {

        public void onClick(View v) {

            Intent i = new Intent(getActivity(),
                    AddActivity.class);
            i.putExtra("update", false);
            startActivity(i);

        }
    });

    //click to update data
    userList.setOnItemClickListener(new OnItemClickListener() {

        public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
                long arg3) {

            Intent i = new Intent(getActivity(),
                    AddActivity.class);
            i.putExtra("Fname", user_fName.get(arg2));
            i.putExtra("Lname", user_lName.get(arg2));
            i.putExtra("ID", userId.get(arg2));
            i.putExtra("update", true);
            startActivity(i);

        }
    });

    //long click to delete data
    userList.setOnItemLongClickListener(new OnItemLongClickListener() {

        public boolean onItemLongClick(AdapterView<?> arg0, View arg1,
                final int arg2, long arg3) {

            build = new AlertDialog.Builder(getActivity());
            build.setTitle("Delete " + user_fName.get(arg2) + " "
                    + user_lName.get(arg2));
            build.setMessage("Do you want to delete ?");
            build.setPositiveButton("Yes",
                    new DialogInterface.OnClickListener() {

                        public void onClick(DialogInterface dialog,
                                int which) {

                            Toast.makeText(
                                    getActivity(),
                                    user_fName.get(arg2) + " "
                                            + user_lName.get(arg2)
                                            + " is deleted.", 3000).show();

                            dataBase.delete(
                                    DbHelper.TABLE_NAME,
                                    DbHelper.KEY_ID + "="
                                            + userId.get(arg2), null);
                            displayData();
                            dialog.cancel();
                        }
                    });

            build.setNegativeButton("No",
                    new DialogInterface.OnClickListener() {

                        public void onClick(DialogInterface dialog,
                                int which) {
                            dialog.cancel();
                        }
                    });
            AlertDialog alert = build.create();
            alert.show();

            return true;
        }
    });
    return view;
}

@Override
public void onResume() {
    displayData();
    super.onResume();
}

/**
 * displays data from SQLite
 */
private void displayData() {
    dataBase = mHelper.getWritableDatabase();
    Cursor mCursor = dataBase.rawQuery("SELECT * FROM "
            + DbHelper.TABLE_NAME, null);

    userId.clear();
    user_fName.clear();
    user_lName.clear();
    if (mCursor.moveToFirst()) {
        do {
            userId.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_ID)));
            user_fName.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_FNAME)));
            user_lName.add(mCursor.getString(mCursor.getColumnIndex(DbHelper.KEY_LNAME)));

        } while (mCursor.moveToNext());
    }
    DisplayAdapter disadpt = new DisplayAdapter(getActivity(),userId, user_fName, user_lName);
    userList.setAdapter(disadpt);
    mCursor.close();
}

}

我收到的错误如下

03-20 13:15:50.108: E/AndroidRuntime(795): FATAL EXCEPTION: main
03-20 13:15:50.108: E/AndroidRuntime(795): java.lang.NullPointerException
03-20 13:15:50.108: E/AndroidRuntime(795):  atapp.norman.tennis.FoursFragment.onCreateView(FoursFragment.java:52)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:795)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:998)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.app.BackStackRecord.run(BackStackRecord.java:622)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1330)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.app.FragmentManagerImpl$1.run(FragmentManager.java:417)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.os.Handler.handleCallback(Handler.java:605)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.os.Handler.dispatchMessage(Handler.java:92)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.os.Looper.loop(Looper.java:137)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.app.ActivityThread.main(ActivityThread.java:4340)
03-20 13:15:50.108: E/AndroidRuntime(795):  at java.lang.reflect.Method.invokeNative(Native Method)
03-20 13:15:50.108: E/AndroidRuntime(795):  at java.lang.reflect.Method.invoke(Method.java:511)
03-20 13:15:50.108: E/AndroidRuntime(795):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-20 13:15:50.108: E/AndroidRuntime(795):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
03-20 13:15:50.108: E/AndroidRuntime(795):  at dalvik.system.NativeStart.main(Native Method)

我真的不介意这是不是一件愚蠢的事情，但我真的不知道发生了什么！谢谢

更换

//add new record
getView().findViewById(...

与

onCreateView（）

中的

getView（）

太早了-您尚未将视图返回到框架，以便

getView（）

返回

03-20 13:15:50.108: E/AndroidRuntime(795): FATAL EXCEPTION: main
03-20 13:15:50.108: E/AndroidRuntime(795): java.lang.NullPointerException
03-20 13:15:50.108: E/AndroidRuntime(795):  atapp.norman.tennis.FoursFragment.onCreateView(FoursFragment.java:52)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:795)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:998)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.app.BackStackRecord.run(BackStackRecord.java:622)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1330)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.app.FragmentManagerImpl$1.run(FragmentManager.java:417)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.os.Handler.handleCallback(Handler.java:605)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.os.Handler.dispatchMessage(Handler.java:92)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.os.Looper.loop(Looper.java:137)
03-20 13:15:50.108: E/AndroidRuntime(795):  at android.app.ActivityThread.main(ActivityThread.java:4340)
03-20 13:15:50.108: E/AndroidRuntime(795):  at java.lang.reflect.Method.invokeNative(Native Method)
03-20 13:15:50.108: E/AndroidRuntime(795):  at java.lang.reflect.Method.invoke(Method.java:511)
03-20 13:15:50.108: E/AndroidRuntime(795):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-20 13:15:50.108: E/AndroidRuntime(795):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
03-20 13:15:50.108: E/AndroidRuntime(795):  at dalvik.system.NativeStart.main(Native Method)

//add new record
getView().findViewById(...

//add new record
view.findViewById(...