Make TextView scrollable without using ScrollView

2 steps, firstly, set scroll bar rotation in AndroidManifest.xml:
         android:scrollbars="vertical"

Then, set the scrolling method for the TextView, mostly in onCreate() function:
        ((TextView)findViewById(R.id.textview)).setMovementMethod(ScrollingMovementMethod.getInstance());

Parent Activity is destroyed when providing Up navigation

If providing Up navigation behavior as Android doc: http://developer.android.com/training/implementing-navigation/ancestral.html, when click the Up button on the navigation bar, the parent activity is destroyed then re-created. It is different behavior as pressing back key.

To avoid destroy parent activity, one solution is setting launch mode <singleTop> for the activity in AndroidManifest.xml:

android:launchMode="singleTop"

The different between Up key and Back key is, when pressing Back key, by default, the currently activity is popup from activity stack and finished, so the previously activity shows up. When pressing Up key, the currently activity is popup from stack too, but the parent activity, which is defined in AndroidManifest.xml and maybe not the previously activity, is created to show. By default the launch mode is <standard> so the existed activity task is destroyed then re-create. To set the launch mode to <singleTop>, Android will launch the existed one instead of create a new task.

Get Android Kernel log

 To catch Kernel log, need a rooted Android device and adb shell worable, then use the adb logcat command:

$adb shell logcat -v time -f /dev/kmsg | cat /proc/kmsg

To  write the output to a file:

$adb shell logcat -v time -f /dev/kmsg | cat /proc/kmsg > /sdcard/log.txt

Get navigation bar (TSB bar) height

The dim value is defined as com.android.internal.R.dimen.navigation_bar_height.

 final int naviHeight = mContext.getResources().getDimensionPixelSize(
                    com.android.internal.R.dimen.navigation_bar_height);

How to exclude activity from recent application list on Android

To forbidden your activity in the recent application list, just define this parameter in AndroidManifest.xml for the activity:

android:excludeFromRecents="true"

for example:
        <activity
            android:name="com.test.MainActivity"
            android:noHistory="true"
            android:screenOrientation="portrait"
            android:excludeFromRecents="true"
            android:label="@string/app_name">
            ......
         </activity>

Monitor screen ON and OFF

Has to register receiver via function registerReceiver(), so usually have to create a service for it.

public  class UpdateService extends Service {

    BroadcastReceiver mReceiver = new BroadcastReceiver {
         private boolean screenOff;

        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction().equals(Intent.ACTION_SCREEN_OFF)) {
                screenOff = true;
            } else if (intent.getAction().equals(Intent.ACTION_SCREEN_ON)) {
                screenOff = false;
            }

            handleScreenAction(screenOff);
        }
    }

    private void handleScreenAction(boolean screenOff) {
        if (screenOff) {
            // your code
        } else {
            // your code
        }
    }

    @Override
    public void onCreate() {
        super.onCreate();
        // register receiver that handles screen on and screen off logic
        IntentFilter filter = new IntentFilter(Intent.ACTION_SCREEN_ON);
        filter.addAction(Intent.ACTION_SCREEN_OFF);
        registerReceiver(mReceiver, filter);
    }

    @Override
    public void onDestory() {
        super.onDestory();
        unRegisterReceiver(mReceiver);
    }

    public void onStart(Context context, Intent intent, int startId) {
    }

    @Override
    public IBinder onBind(Intent intent) {
        // TODO Auto-generated method stub
        return null;
    }
}

Detect headset / Bluetooth status

need this permission:
<uses-permission android:name="android.permission.BLUETOOTH"></uses-permission>

and code snap:
                AudioManager audioManager = (AudioManager)context.getSystemService(Context.AUDIO_SERVICE);
                if (audioManager.isWiredHeadsetOn()
                        || audioManager.isBluetoothA2dpOn()
                        || audioManager.isBluetoothScoOn() ) {
      // headset connected
}