File Explorer, access SD Card on Samsung Galaxy S3

In the exercise of "File Explorer", the root is set as Environment.getExternalStorageDirectory(). But if you run it on Samsung Galaxy S3, it cannot access the removable external SD Card. It's because what getExternalStorageDirectory() return is /storage/sdcard0, but the SD Card is mounted on /storage/extSdCard, not under the tree of /storage/sdcard0. To solve this case, we have to set root as Environment.getExternalStorageDirectory().getParent(), it's /storage.

package com.example.androidexplorer;

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

import android.os.Bundle;
import android.os.Environment;
import android.app.AlertDialog;
import android.app.ListActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;

public class MainActivity extends ListActivity {
 
 private List<String> item = null;
 private List<String> path = null;
 private String root;
 private TextView myPath;
 
 private String currentPath;
 Comparator<? super File> comparator;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myPath = (TextView)findViewById(R.id.path);
        
        comparator = filecomparatorByAlphabetically;
        //root = Environment.getExternalStorageDirectory().getPath();
        root = Environment.getExternalStorageDirectory().getParent();
        getDir(root);
        
        Button btnAlphabetically = (Button)findViewById(R.id.button_alphabetically);
        btnAlphabetically.setOnClickListener(new OnClickListener(){

   @Override
   public void onClick(View arg0) {
    comparator = filecomparatorByAlphabetically;
    getDir(currentPath);
    
   }});
        
        Button btnLastDateModified = (Button)findViewById(R.id.button_lastDateModified);
        btnLastDateModified.setOnClickListener(new OnClickListener(){

   @Override
   public void onClick(View arg0) {
    comparator = filecomparatorByLastModified;
          getDir(currentPath);
    
   }});
    }
    
    private void getDir(String dirPath)
    {
     currentPath = dirPath;
     
     myPath.setText("Location: " + dirPath);
     item = new ArrayList<String>();
     path = new ArrayList<String>();
     File f = new File(dirPath);
     File[] files = f.listFiles();
     
     if(!dirPath.equals(root))
     {
      item.add(root);
      path.add(root);
      item.add("../");
      path.add(f.getParent()); 
     }
     
     Arrays.sort(files, comparator);
     
     for(int i=0; i < files.length; i++)
     {
      File file = files[i];
      
      if(!file.isHidden() && file.canRead()){
       path.add(file.getPath());
          if(file.isDirectory()){
           item.add(file.getName() + "/");
          }else{
           item.add(file.getName());
          }
      } 
     }

     ArrayAdapter<String> fileList =
       new ArrayAdapter<String>(this, R.layout.row, item);
     setListAdapter(fileList); 
    }
    
    Comparator<? super File> filecomparatorByLastModified = new Comparator<File>(){
  
  public int compare(File file1, File file2) {

   if(file1.isDirectory()){
    if (file2.isDirectory()){
     return Long.valueOf(file1.lastModified()).compareTo(file2.lastModified());
    }else{
     return -1;
    }
   }else {
    if (file2.isDirectory()){
     return 1;
    }else{
     return Long.valueOf(file1.lastModified()).compareTo(file2.lastModified());
    }
   }
    
  }  
 };
    
    Comparator<? super File> filecomparatorByAlphabetically = new Comparator<File>(){
  
  public int compare(File file1, File file2) {

   if(file1.isDirectory()){
    if (file2.isDirectory()){
     return String.valueOf(file1.getName().toLowerCase()).compareTo(file2.getName().toLowerCase());
    }else{
     return -1;
    }
   }else {
    if (file2.isDirectory()){
     return 1;
    }else{
     return String.valueOf(file1.getName().toLowerCase()).compareTo(file2.getName().toLowerCase());
    }
   }
    
  }  
 };
 
 @Override
 protected void onListItemClick(ListView l, View v, int position, long id) {
  // TODO Auto-generated method stub
  File file = new File(path.get(position));
  
  if (file.isDirectory())
  {
   if(file.canRead()){
    getDir(path.get(position));
   }else{
    new AlertDialog.Builder(this)
     .setIcon(R.drawable.ic_launcher)
     .setTitle("[" + file.getName() + "] folder can't be read!")
     .setPositiveButton("OK", null).show(); 
   } 
  }else {
   new AlertDialog.Builder(this)
     .setIcon(R.drawable.ic_launcher)
     .setTitle("[" + file.getName() + "]")
     .setPositiveButton("OK", null).show();

    }
 }

}

Download the files.

Please notice that it's not a standard approach. For example, if you run it on Nexus One, you will see some un-expected folder in /storage.