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
}

How to detect whether phone is in charging

Does not need register a broadcast receiver. Call function
registerReceiver(null, new IntentFilter(Intent.ACTION_BATTERY_CHANGED)), and it will return anIntent with battery status immediately, because Intent.ACTION_BATTERY_CHANGED is a sticky broadcast.

Here is code snap:
        Intent intent = context.registerReceiver(null, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
        int plugged = intent.getIntExtra(BatteryManager.EXTRA_PLUGGED, -1);
        boolean cableCharge = plugged == BatteryManager.BATTERY_PLUGGED_USB
                || plugged == BatteryManager.BATTERY_PLUGGED_AC;
        boolean wirelessCharge = plugged == BatteryManager.BATTERY_PLUGGED_WIRELESS;

Translate touch event coordinates to the parent

The touch event coordinates can be got in onTouch() by MotionEvent:getX() and

MotionEvent:getY(), the coordinates are based on currently view. To translate to the parent layout, just append the current view positions to them like this:

 

view.getLeft() + motionEvent.getX();

view.getTop() + motionEvent.getY(); 

 

Haptic feedback (vibration) on Android

Simple use View:performHapticFeedback() to play a vibration:

View view = findViewById(...)
view.performHapticFeedback(HapticFeedbackConstants.VIRTUAL_KEY);