Chia sẻ code hay để dễ dàng tìm kiếm khi cần sử dụng.
Xem post chính tại đây.
Link :  https://gist.github.com

1. Replace fragment kèm theo Animation // By Phúc Lưu Ngọc

private void replaceFragment(Fragment fragment) {
FragmentManager manager = getSupportFragmentManager();
FragmentTransaction transaction = manager.beginTransaction();
transaction.setCustomAnimations(R.anim.slide_in_right,R.anim.slide_out_left)
.replace(R.id.content_main, fragment)
.addToBackStack(null)
.commit();
}

2. Chuyển đơn vị dp thành pixel  //Nguyễn Linh

public static int convertDpToPixel(int dp) {

        Resources r = Resources.getSystem();
        return Math.round(dp * (r.getDisplayMetrics().densityDpi / 160f));
    }

3. Lib Thư viện Utils // Tran Tien Tin
https://github.com/changer/android-utils
https://github.com/Trinea/android-common/tree/master/src/cn/trinea/android/common/util

4. PLAY MP3 FROM INTERNET + LOCAL //KHOAPHAM

- From local:
MediaPlayer song = MediaPlayer.create(MainActivity.this, R.raw.nuocmat); 
song.start();

Stop: 
onPause(); 
song.pause();

- From Internet:
  public void PlayNhacMp3(String url){
        //url = "http://khoapham.vn/download/vietnamoi.mp3";
        MediaPlayer mediaPlayer = new MediaPlayer();
        mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
        try {
            mediaPlayer.setDataSource(url);
            mediaPlayer.prepareAsync();
            mediaPlayer.setOnPreparedListener(new MediaPlayer.OnPreparedListener() {
                @Override
                public void onPrepared(MediaPlayer mp) {
                    mp.start();
                }
            });

        } catch (IOException e) {
            e.printStackTrace();
        }

    }

5. SAVE + READ FILE TXT //KHOAPHAM

- Save file txt

FileOutputStream fos = openFileOutput("khoapham.txt", Context.MODE_PRIVATE); 
fos.write(noidung.getBytes());
fos.close()

- Read file txt

FileInputStream fis = openFileInput("khoapham.txt"); 
BufferedReader br = new BufferedReader(new InputStreamReader(new DataInputStream(fis))); 
String line = ""; 
while( (line = br.readLine()) != null ){ 
txtvNoiDung.append(line); 
txtvNoiDung.append("\n"); 
}

6. LẤY KÍCH THƯỚC CỦA MÀN HÌNH THIẾT BỊ //KHOAPHAM

Display display = ((WindowManager) getSystemService(WINDOW_SERVICE)).getDefaultDisplay(); 
int width = display.getWidth(); 
int height = display.getHeight(); 
int ori = display.getOrientation();

7. CONVERT FILE LOCAL TO BYTE[] //KHOAPHAM

public byte[] FileLocal_To_Byte(String path){
        File file = new File(path);
        int size = (int) file.length();
        byte[] bytes = new byte[size];
        try {
            BufferedInputStream buf = new BufferedInputStream(new FileInputStream(file));
            buf.read(bytes, 0, bytes.length);
            buf.close();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return bytes;
}

8. Lớp Toast Utils // Huy NQ
https://goo.gl/tLf32v

9. Get TypeFace

public static Typeface getTypefaceFont(Context context) {
    return Typeface.createFromAsset(context.getAssets(), "Gilroy-Light.otf");
}

10. Format money Việt Nam

 //Convert long to money type
    public static String formatNumber(long number) {
        if (number < 1000) {
            return String.valueOf(number);
        }
        try {
            NumberFormat formatter = new DecimalFormat("###,###");
            String resp = formatter.format(number);
            resp = resp.replaceAll(",", ".");
            return resp;
        } catch (Exception e) {
            return "";
        }
    }

11. Check EditText Empty

 public static  boolean isEmpty(EditText etText) {
        if (etText.getText().toString().trim().length() > 0) {
            return true;
        } else {
            etText.requestFocus();
            etText.setError("Vui lòng điền thông tin!");
            return false;
        }
    }

12. Class MyClipboardManager

https://gist.github.com/nguyenlinhnttu/afa2c8d07074f804b7591ffb2bf7cbd3

13. Get String Resource 

public static String getStringFromResources(Context context, int id) {
        return context.getResources().getString(id);
    }

14. Convert long time to  simple Date

public static String convertLongToDay(long timeStamp) {
        DateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");
        Date date = new Date(timeStamp);
        return  dateFormat.format(date);
    }

15. Check Email valid

public static boolean isEmailValid(String email) {
        boolean isValid = false;

        String expression = "[a-zA-Z0-9._-]+@[a-z]+(\\.+[a-z]+)+";
        CharSequence inputStr = email;

        Pattern pattern = Pattern.compile(expression, Pattern.CASE_INSENSITIVE);
        Matcher matcher = pattern.matcher(inputStr);
        if (matcher.matches()) {
            isValid = true;
        }
        return isValid;
    }

Hoặc: // By Dong Hai

public final static boolean isValidEmail(CharSequence target) {
if (TextUtils.isEmpty(target)) {
return false;
} else {
return android.util.Patterns.EMAIL_ADDRESS.matcher(target).matches();
}
}

16. Các lib hay trên github 

• Animation: https://github.com/2359media/EasyAndroidAnimations
• MaterialDesign : https://github.com/lightSky/Awesome-MaterialDesign
• NavigationTabBar: https://github.com/DevLight-Mobile-Agency/NavigationTabBar
• Animation TextView: https://github.com/hanks-zyh/HTextView
• CircleImageView: https://github.com/hdodenhof/CircleImageView
• MPAndroidChart: https://github.com/PhilJay/MPAndroidChart
• Material-Animations: https://github.com/lgvalle/Material-Animations

17: Sử dụng RecyclerView

https://goo.gl/cHWRSD

18: Tutorial Retrofit 2

Tiếng việt: https://goo.gl/VQ8zYt

Tiếng Anh : https://goo.gl/tcRSoQ

19: Thư viện Glide

Tiếng việt: https://goo.gl/vKRQQn

Tiếng Anh: https://goo.gl/8qsB7s

20. Thư viện bind view Butter Knife

Home: http://jakewharton.github.io/butterknife/

21: Google Play Rate app, Share App FB via package, Send GMail // By Nguyễn Chiến
https://gist.github.com/nguyenlinhnttu/c14fa16d85097db6a7b49f7402811e65

22:Privacy Nguyễn Hà Đông (Tham Khảo)
http://www.dotgears.com/privacy.html

23. Một số hàm được chia sẻ bởi  // Chan Doi

https://goo.gl/sJk8D1

24. AsyncTask Multiple param result multi value

https://goo.gl/XtXHQs

25. Một số Intent implicit thường dùng

https://goo.gl/IFx609

26. Sử dụng CountDownTimer

new CountDownTimer(30000, 1000) {

    public void onTick(long millisUntilFinished) {
        mTextField.setText("seconds remaining: " + millisUntilFinished / 1000);
       //here you can have your logic to set text to edittext
    }

    public void onFinish() {
        mTextField.setText("done!");
    }

}.start();

27. Delay with Handler

final Handler handler = new Handler();
handler.postDelayed(new Runnable() {
    @Override
    public void run() {
        // Do something after 5s = 5000ms
     
    }
}, 5000);