Implement custom file explorer dialog

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/customdialog"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:padding="20dp"
    android:minWidth="300dp">
    <LinearLayout 
        android:orientation="horizontal"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_margin="10dp">
        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/ic_launcher"/>
        <Button
            android:id="@+id/up"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="Parent folder"/>
    </LinearLayout>

 <TextView
     android:id="@+id/folder"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
    <ListView
        android:id="@+id/dialoglist"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

package com.AndroidCustomDialog;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

import android.app.Activity;
import android.app.Dialog;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

public class AndroidCustomDialogActivity extends Activity {

 Button buttonOpenDialog;
 Button buttonUp;
 TextView textFolder;
 
 String KEY_TEXTPSS = "TEXTPSS";
 static final int CUSTOM_DIALOG_ID = 0;
 
 ListView dialog_ListView;
 
 File root;
 File curFolder;
 
 private List<String> fileList = new ArrayList<String>();
 
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        buttonOpenDialog = (Button)findViewById(R.id.opendialog);
        buttonOpenDialog.setOnClickListener(new Button.OnClickListener(){

   @Override
   public void onClick(View arg0) {
    showDialog(CUSTOM_DIALOG_ID);
   }});

        root = new File(Environment
          .getExternalStorageDirectory()
          .getAbsolutePath());
        
        curFolder = root;
  
    }

 @Override
 protected Dialog onCreateDialog(int id) {

  Dialog dialog = null;
  
  switch(id) {
     case CUSTOM_DIALOG_ID:
      dialog = new Dialog(AndroidCustomDialogActivity.this);
      dialog.setContentView(R.layout.dialoglayout);
      dialog.setTitle("Custom Dialog");
      
      dialog.setCancelable(true);
      dialog.setCanceledOnTouchOutside(true);
      
      textFolder = (TextView)dialog.findViewById(R.id.folder);

      buttonUp = (Button)dialog.findViewById(R.id.up);
      buttonUp.setOnClickListener(new OnClickListener(){

    @Override
    public void onClick(View v) {
     // TODO Auto-generated method stub
     ListDir(curFolder.getParentFile());
    }});

      //Prepare ListView in dialog
      dialog_ListView = (ListView)dialog.findViewById(R.id.dialoglist);

      dialog_ListView.setOnItemClickListener(new OnItemClickListener(){

    @Override
    public void onItemClick(AdapterView<?> parent, View view,
      int position, long id) {
     
     File selected = new File(fileList.get(position));
     if(selected.isDirectory()){
      ListDir(selected); 
     }else {
      Toast.makeText(AndroidCustomDialogActivity.this,
        selected.toString() + " selected",
        Toast.LENGTH_LONG).show();
      dismissDialog(CUSTOM_DIALOG_ID);
        }
     
    }});
      
         break;
     }

  return dialog;
 }

 @Override
 protected void onPrepareDialog(int id, Dialog dialog, Bundle bundle) {
  // TODO Auto-generated method stub
  super.onPrepareDialog(id, dialog, bundle);

  switch(id) {
     case CUSTOM_DIALOG_ID:
      ListDir(curFolder);
         break;
     }
  
 }
 
 void ListDir(File f){

  if(f.equals(root)){
   buttonUp.setEnabled(false);
  }else{
   buttonUp.setEnabled(true);
  }
  
  curFolder = f;
  textFolder.setText(f.getPath());
  
  File[] files = f.listFiles();
  fileList.clear();
  for (File file : files){
   fileList.add(file.getPath());   
  }
       
  ArrayAdapter<String> directoryList
   = new ArrayAdapter<String>(this,
     android.R.layout.simple_list_item_1, fileList);
  dialog_ListView.setAdapter(directoryList);
 }

}

<?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="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello" />

    <Button
        android:id="@+id/opendialog"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Open Dialog" />

</LinearLayout>