Google Android - это несложно

Код: Выделить всё

public class FileManager extends ListActivity {
    private List<String> directoryEntries = new ArrayList<String>();
    private File currentDirectory = new File("/");
    //when application started
    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        //set main layout
        setContentView(R.layout.activity_file_manager);
        //browse to root directory
        browseTo(new File("/"));
    }

    //browse to parent directory
    private void upOneLevel(){
        if(this.currentDirectory.getParent() != null) {
            this.browseTo(this.currentDirectory.getParentFile());
        }
    }

    //browse to file or directory
    private void browseTo(final File aDirectory){
        //if we want to browse directory
        if (aDirectory.isDirectory()){
            //fill list with files from this directory
            this.currentDirectory = aDirectory;
            fill(aDirectory.listFiles());

            //set titleManager text
            TextView titleManager = (TextView) findViewById(R.id.titleManager);
            titleManager.setText(aDirectory.getAbsolutePath());
        } else {
            //if we want to open file, show this dialog:
            //listener when YES button clicked
            OnClickListener okButtonListener = new OnClickListener(){
                public void onClick(DialogInterface arg0, int arg1) {
                    //intent to navigate file
                    Intent i = new Intent(FileManager.this, graph_content.class);
                    i.putExtra("path", aDirectory.getAbsolutePath());
                    startActivity(i);
                }
            };
            //listener when NO button clicked
            OnClickListener cancelButtonListener = new OnClickListener() {
                public void onClick(DialogInterface arg0, int arg1) {
                    //do nothing
                    //or add something you want
                }
            };

            //create dialog
            new AlertDialog.Builder(this)
                    .setTitle("Подтверждение") //title
                    .setMessage("Хотите открыть файл "+ aDirectory.getName() + "?") //message
                    .setPositiveButton("Да", okButtonListener) //positive button
                    .setNegativeButton("Нет", cancelButtonListener) //negative button
                    .show(); //show dialog
        }
    }
    //fill list
    private void fill(File[] files) {
        //clear list
        this.directoryEntries.clear();

        if (this.currentDirectory.getParent() != null)
            this.directoryEntries.add("..");

        //add every file into list
        for (File file : files) {
            this.directoryEntries.add(file.getAbsolutePath());
        }

        //create array adapter to show everything
        ArrayAdapter<String> directoryList = new ArrayAdapter<String>(this, R.layout.activity_row, this.directoryEntries);
        this.setListAdapter(directoryList);
    }



    //when you clicked onto item
    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        //get selected file name
        int selectionRowID = position;
        String selectedFileString = this.directoryEntries.get(selectionRowID);

        //if we select ".." then go upper
        if(selectedFileString.equals("..")){
            this.upOneLevel();
        } else {
            //browse to clicked file or directory using browseTo()
            File clickedFile = null;
            clickedFile = new File(selectedFileString);
            if (clickedFile != null)
                this.browseTo(clickedFile);
        }
    }
}

Код: Выделить всё

public class graph_content extends Activity {

    private EditText mEdit; // текстовое поле
    private String filepath; //

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Intent intent = getIntent();
        mEdit = (EditText) findViewById(R.id.editText);
        if (intent != null && intent.hasExtra("path")) {
            filepath = intent.getStringExtra("path");
        } else {
            finish();
        }
        openFile(filepath);
    }

    // Метод для открытия файла
    private void openFile(String fileName) {
        try {

            InputStream inputstream = openFileInput(fileName);

            if (inputstream != null) {
                InputStreamReader isr = new InputStreamReader(inputstream);
                BufferedReader reader = new BufferedReader(isr);
                String str;
                StringBuffer buffer = new StringBuffer();

                while ((str = reader.readLine()) != null) {
                    buffer.append(str + "\n");
                }

                inputstream.close();
                mEdit.setText(buffer.toString());
            }
        } catch (Throwable t) {
            Toast.makeText(getApplicationContext(),
                    "Exception: " + t.toString(), Toast.LENGTH_LONG).show();
        }
    }

Код: Выделить всё

 InputStream inputstream = openFileInput(fileName);

Код: Выделить всё

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>

Код: Выделить всё

InputStream inputstream = openFileInput(fileName); 

Код: Выделить всё

 InputStream inputstream = getAssets().open(fileName);