错误SeachView过滤android

Question

我正在为listview创建一个过滤器，我从json获取数据。 这是我的代码 SearchView：

@Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        final SearchView searchView = (SearchView) MenuItemCompat.getActionView(menu.findItem(R.id.action_search));
        SearchManager searchManager = (SearchManager) getSystemService(SEARCH_SERVICE);

        searchView.setSearchableInfo(searchManager.getSearchableInfo(getComponentName()));
        searchView.setOnQueryTextListener(this);

        return true;

    }@Override
    public boolean onQueryTextChange(String newText) {
        if (TextUtils.isEmpty(newText)){
            adapter.getFilter().filter("");
            lv.clearTextFilter();
        }else {
            adapter.getFilter().filter(newText.toString());
        }
        return true;
    }

点击搜索按钮后，这是我的logcat

    FATAL EXCEPTION: main
    Process: com.example.trung.flashcardenglish, PID: 5400
    java.lang.NullPointerException: Attempt to invoke virtual method 'android.widget.Filter android.widget.ArrayAdapter.getFilter()' on a null object reference
    at com.example.trung.flashcardenglish.ielts.Ielts.onQueryTextChange(Ielts.java:244)
    at android.support.v7.widget.SearchView.onTextChanged(SearchView.java:1150)
    at android.support.v7.widget.SearchView.access$2000(SearchView.java:103)
    at android.support.v7.widget.SearchView$12.onTextChanged(SearchView.java:1680)
    at android.widget.TextView.sendOnTextChanged(TextView.java:7679)
    at android.widget.TextView.setText(TextView.java:4060)

这是我的适配器：

lv.setAdapter（适配器）;     lv.setOnItemClickListener（new AdapterView.OnItemClickListener（）{

    @Override
    public void onItemClick(AdapterView<?> parent, View view,
                            int position, long id) {

        String pid = ((TextView) view.findViewById(R.id.pid)).getText()
                .toString();
        String vocabulary = ((TextView) view.findViewById(R.id.vocabulary)).getText()
                .toString();                
        Intent in = new Intent(getApplicationContext(),
                ielts_detail.class);              
        in.putExtra(TAG_PID, pid);
        in.putExtra(TAG_VOCABULARY, vocabulary);
        startActivity(in);

        startActivityForResult(in, 100);
    }
});

}