如何在Android中实现跳转到文件夹？

Question

我正在开发Android的文件管理器。最初的任务是实现一个活动，显示SD卡上的文件夹列表，我设法做到了。 现在我可以在SD卡上看到文件夹列表。但我无法在我的应用程序中打开这些文件夹以查看其中的文件夹。如何实现此功能？
请帮忙！这个问题让我发疯了）

这是我的代码：

public class MainActivity extends Activity  {
    private ListView mListView;
    private List<String> fileNameList;
    private FlAdapter mAdapter;
    private File file;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mListView = (ListView) findViewById(R.id.listView1);
        file = Environment.getExternalStorageDirectory();
        fileNameList = getFileListfromSDCard();
        mAdapter = new FlAdapter(this, R.layout.list_item, fileNameList);
        mListView.setAdapter(mAdapter);
    }

    private List<String> getFileListfromSDCard() {
        String state = Environment.getExternalStorageState();
        List<String> flLst = new ArrayList<String>();
        if (Environment.MEDIA_MOUNTED.equals(state) && file.isDirectory()) {
            File[] fileArr = file.listFiles();
            int length = fileArr.length;
            for (int i = 0; i < length; i++) {
                File f = fileArr[i];
                flLst.add(f.getName());
            }
        }
        return flLst;
    }

    public class FlAdapter extends ArrayAdapter<String> {
        private List<String> fLst;
        private Context adapContext;

        public FlAdapter(Context context, int textViewResourceId,
                         List<String> fLst) {
            super(context, textViewResourceId, fLst);
            this.fLst = fLst;
            adapContext = context;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View view = convertView;
            FHolder fHolder = null;

            if (convertView == null) {
                view = View.inflate(adapContext, R.layout.list_item, null);

                fHolder = new FHolder();
                fHolder.fNameView = (TextView) view.findViewById(R.id.fname);

                view.setTag(fHolder);
            } else {
                fHolder = (FHolder) view.getTag();
            }
            String fileName = fLst.get(position);
            fHolder.fNameView.setText(fileName);

            return view;
        }
    }

    static class FHolder {
        public TextView fNameView;
    }
}

activity_main.xml中

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <ListView
        android:id="@+id/listView1"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />

</RelativeLayout>

list_item.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <TextView
        android:id="@+id/fname"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Large Text"
        android:textAppearance="?android:attr/textAppearanceLarge" />

</RelativeLayout>