android 中WebView 控件在fragment中为什么不显示内容？?报错

我在一个fragment中定义了一个webview布局如下：

<LinearLayout 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"
    android:orientation="vertical"
    android:background="@color/white"
    tools:context=".Fragment2" >

    <LinearLayout
        android:layout_height="45dp"
        android:layout_width="fill_parent"
        android:orientation="vertical"
        android:gravity="center"
        android:background="@drawable/nav_title_bg"
        >
    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/title2"
        android:gravity="center"
        android:textColor="@color/ivory"
        android:textSize="14sp"
        />
    </LinearLayout>
   
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="5dp"
        android:layout_marginRight="5dp"
        android:orientation="horizontal"
        >
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="服务类别："
            />
  <Spinner
      android:id="@+id/typelist"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_weight="1"
      />
  <Button
      android:id="@+id/goodstypequerybt"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="@string/statistics"
     
      />
   </LinearLayout>
   <ScrollView
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       >
      <LinearLayout
          android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:orientation="vertical"
          >
          <TextView
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:text="测试"
              />
    <WebView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/chart1"
        android:background="#000000"
        android:visibility="visible"
        />
    </LinearLayout>
    </ScrollView>
</LinearLayout>

在代码中想实现webview加载本地html，代码如下：

public class Fragment2 extends Fragment {

 private Spinner spinner=null;
 private static final String[] m={"a","b","c","d","e"};  
 
 private WebView wv=null;
 private ArrayAdapter<String> adapter;
 @Override
 public void onCreate(Bundle savedInstanceState) {
  // TODO Auto-generated method stub
  super.onCreate(savedInstanceState);
 }

 
 @Override
 public View onCreateView(LayoutInflater inflater, ViewGroup container,
   Bundle savedInstanceState) {
  // TODO Auto-generated method stub
  View view=inflater.inflate(R.layout.fragment2, container,false);
  wv=(WebView)view.findViewById(R.id.chart1);
  wv.getSettings().setJavaScriptEnabled(true);  //设置WebView支持javascript
  wv.getSettings().setUseWideViewPort(true);//设置是当前html界面自适应屏幕
  wv.getSettings().setSupportZoom(true); //设置支持缩放
  wv.getSettings().setBuiltInZoomControls(true);//显示缩放控件
  wv.getSettings().setLoadWithOverviewMode(true);
  wv.getSettings().setDefaultTextEncodingName("utf-8");
  wv.requestFocus();
  wv.loadUrl("file:///android_asset/hello.html"); //加载assert目录下的文件
  //wv.loadData("hello", "text/html", "utf-8");
  
  
  this.spinner=(Spinner)view.findViewById(R.id.typelist);
   //将可选内容与ArrayAdapter连接起来  
  adapter = new ArrayAdapter<String>(getActivity(),android.R.layout.simple_spinner_item,m);  
   //设置下拉列表的风格  
  adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);  
  //将adapter 添加到spinner中  
  spinner.setAdapter(adapter);
  this.spinner.setPrompt("请选择类型");
  spinner.setVisibility(view.VISIBLE);
  return view;
 }

 
 @Override
 public void onDestroy() {
  // TODO Auto-generated method stub
  super.onDestroy();
 }

 @Override
 public void onDestroyOptionsMenu() {
  // TODO Auto-generated method stub
  super.onDestroyOptionsMenu();
 }

 @Override
 public void onStart() {
  // TODO Auto-generated method stub
  super.onStart();
 }

 @Override
 public void onStop() {
  // TODO Auto-generated method stub
  super.onStop();
 }

}

为什么在运行的时候没有报错，却也显示不了webview中的内容呢？求指教~