findViewById返回Null,该如何解决

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent" android:layout_height="wrap_content"    android:orientation="vertical">    <ScrollView android:layout_width="fill_parent"        android:layout_height="wrap_content">        <LinearLayout android:gravity="center_vertical"            android:orientation="vertical" android:paddingLeft="12.0dip"            android:paddingRight="12.0dip" android:layout_width="fill_parent"            android:layout_height="fill_parent">            <TextView android:layout_width="fill_parent" android:layout_height="wrap_content"                 android:textSize="18.0dip" android:textStyle="bold"                 android:layout_marginTop="3.0dip" android:text="@string/keyword" />            <EditText android:id="@id/keywordEditText"                android:layout_width="fill_parent" android:layout_height="wrap_content"                android:hint="@string/keyword_hint" />            <TextView android:layout_width="fill_parent" android:layout_height="wrap_content"                 android:textSize="18.0dip" android:textStyle="bold"                 android:layout_marginTop="6.0dip" android:text="@string/scope" />            <Spinner android:id="@id/scopeSpinner" style="@style/filter_spinner" />            <TextView android:layout_width="fill_parent" android:layout_height="wrap_content"                 android:textSize="18.0dip" android:textStyle="bold"                 android:layout_marginTop="6.0dip" android:text="@string/lawno" />            <EditText android:id="@id/lawnoEditText"                android:layout_width="fill_parent" android:layout_height="wrap_content"                android:hint="@string/lawno_hint" />            <TextView android:layout_width="fill_parent" android:layout_height="wrap_content"                 android:textSize="18.0dip" android:textStyle="bold"                 android:layout_marginTop="6.0dip" android:text="@string/valid" />            <Spinner android:id="@id/validSpinner" style="@style/filter_spinner" />            <TextView android:layout_width="fill_parent" android:layout_height="wrap_content"                 android:textSize="18.0dip" android:textStyle="bold"                 android:layout_marginTop="6.0dip" android:text="@string/area" />            <Spinner android:id="@id/areaSpinner" style="@style/filter_spinner" />            <TextView android:layout_width="fill_parent" android:layout_height="wrap_content"                 android:textSize="18.0dip" android:textStyle="bold"                 android:layout_marginTop="6.0dip" android:text="@string/category" />            <Spinner android:id="@id/categorySpinner" style="@style/filter_spinner" />            <TextView android:layout_width="fill_parent" android:layout_height="wrap_content"                 android:textSize="18.0dip" android:textStyle="bold"                 android:layout_marginTop="6.0dip" android:text="@string/pubunit" />            <EditText android:id="@id/pubunitEditText"                android:layout_width="fill_parent" android:layout_height="wrap_content"                android:hint="@string/pubunit_hint" />            <TextView android:layout_width="fill_parent" android:layout_height="wrap_content"                 android:textSize="18.0dip" android:textStyle="bold"                 android:layout_marginTop="6.0dip" android:text="@string/pubdate" />            <EditText id="@id/pubdateEditText"                 android:layout_width="fill_parent" android:layout_height="wrap_content"                android:hint="@string/pubdate_hint"/>            <TextView android:layout_width="fill_parent" android:layout_height="wrap_content"                 android:textSize="18.0dip" android:textStyle="bold"                 android:layout_marginTop="6.0dip" android:text="@string/pubdateto" />            <EditText id="@id/pubdatetoEditText"                 android:layout_width="fill_parent" android:layout_height="wrap_content"                android:hint="@string/pubdateto_hint"/>                            <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"                android:layout_width="fill_parent" android:layout_height="wrap_content"                android:gravity="center" android:padding="10dip">                <Button android:id="@id/filterSearchBtn" android:layout_height="wrap_content"                    android:layout_width="75dip" android:text="@string/search"/>                <Button android:id="@id/filterResetBtn" android:layout_height="wrap_content"                    android:layout_width="75dip" android:text="@string/reset"/>                <Button android:id="@id/filterCancelBtn" android:layout_height="wrap_content"                    android:layout_width="75dip" android:text="@string/cancel"/>            </LinearLayout>        </LinearLayout>    </ScrollView></LinearLayout> 

public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                inflater = LayoutInflater.from(MainActivity.this);        initTitleBar();        initFilterDialog();        initMainList();    }......public void initFilterDialog(){        //初始化变量        final View dialogView = inflater.inflate(R.layout.filter, null);        keywordEditText = (EditText) dialogView.findViewById(R.id.keywordEditText);        scopeSpinner = (Spinner) dialogView.findViewById(R.id.scopeSpinner);        lawnoEditText = (EditText) dialogView.findViewById(R.id.lawnoEditText);        validSpinner = (Spinner) dialogView.findViewById(R.id.validSpinner);        areaSpinner = (Spinner) dialogView.findViewById(R.id.areaSpinner);        categorySpinner = (Spinner) dialogView.findViewById(R.id.categorySpinner);        pubunitEditText = (EditText) dialogView.findViewById(R.id.pubunitEditText);        searchButton = (Button) dialogView.findViewById(R.id.filterSearchBtn);        searchButton.setOnClickListener(new OnClickEvent());        resetButton = (Button) dialogView.findViewById(R.id.filterResetBtn);        resetButton.setOnClickListener(new OnClickEvent());        cancelButton = (Button) dialogView.findViewById(R.id.filterCancelBtn);        cancelButton.setOnClickListener(new OnClickEvent());        pubdateEditText = (EditText) dialogView.findViewById(R.id.pubdateEditText);        pubdateEditText.setOnClickListener(new OnClickEvent()); //错误在这！！！        pubdatetoEditText = (EditText) dialogView.findViewById(R.id.pubdatetoEditText);        pubdatetoEditText.setOnClickListener(new OnClickEvent());        final Calendar c = Calendar.getInstance();         datePickerDialog = new DatePickerDialog(MainActivity.this,new DatePickerDialog.OnDateSetListener() {            public void onDateSet(DatePicker view, int year, int monthOfYear,                    int dayOfMonth) {                datePickerDialogTarget.setText(year+""+monthOfYear+""+dayOfMonth);            }        },c.get(Calendar.YEAR),c.get(Calendar.MONTH),c.get(Calendar.DAY_OF_MONTH));//        datePickerDialog.setButton("设置", null);        //创建面板        AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);        builder.setIcon(R.drawable.m_filter);        builder.setTitle(R.string.filter);        builder.setView(dialogView);        filterDialog=builder.create();    }