Android Folder Structure

Hello! I am starting my studies in Android development, I am trying to list and link the folders of the Android Memory, either internal or external. I can already list and display in a Listview or LinearLayout, but how do I when the user clicks on some folder it enters into it and update the LinearLayout with the files from within this folder? In a File Explorer scheme, the user can enter the folder, go back or open the files.

Here's what I have today:

**activity_main.xml**

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <TextView android:id="@+id/textview"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Get File Name From SDCard"
        android:textSize="18dp"
        android:gravity="center"
        android:layout_marginTop="10dp"
        />
    <RelativeLayout android:id="@+id/relativeLayout1"
        android:layout_height="wrap_content"
        android:layout_width="wrap_content">
        <EditText
            android:layout_alignParentLeft="true"
            android:hint="Pesquisar"
            android:id="@+id/editText"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="5dp"
            android:layout_marginRight="5dp"
            android:layout_marginTop="15dp"
            android:ems="10"
            android:inputType="textPersonName"
            android:layout_toLeftOf="@+id/skipButton" >
        </EditText>

        <Button android:text="Browser"
            android:id="@+id/skipButton"
            android:textSize="18dp"
            android:layout_marginTop="10dp"
            android:layout_alignParentRight="true"
            android:layout_height="wrap_content"
            android:layout_width="wrap_content"
            android:onClick="getfile" >
        </Button>
    </RelativeLayout>
</LinearLayout>

**MainActivity.java**

LinearLayout view = (LinearLayout) findViewById(R.id.view);

        //getting SDcard root path
        root = new File(Environment.getExternalStorageDirectory().getAbsolutePath());
        getfile(root);

        for (int i = 0; i < fileList.size(); i++) {
            TextView textView = new TextView(this);
            textView.setText(fileList.get(i).getName());
            textView.setPadding(5, 5, 5, 5);

            //System.out.println("fileList.get(i).getName(): " + fileList.get(i).getName());

            if (fileList.get(i).isDirectory()) {
                textView.setTextColor(Color.parseColor("#FF0000"));
            }

            view.addView(textView);
        }


    //----------------------------------------------------------

    public ArrayList<String> GetFiles(String DirectoryPath) {
        ArrayList<String> MyFiles = new ArrayList<String>();
        File f = new File(DirectoryPath);

        f.mkdirs();
        File[] files = f.listFiles();
        if (files.length == 0)
            return null;
        else {
            for (int i=0; i<files.length; i++)
                MyFiles.add(files[i].getName());
        }

        return MyFiles;
    }

Thanks for everyone's help.