android.service.overlayWindow

android-service-overlayWindow.java

// prepare
// AndroidManifest.xml add permission
// <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
// see http://stackoverflow.com/questions/7569937/unable-to-add-window-android-view-viewrootw44da9bc0-permission-denied-for-t
WindowManager mWm = (WindowManager) getSystemService(WINDOW_SERVICE);
mTextView = new TextView(this);
mLayoutParam = new WindowManager.LayoutParams(
WindowManager.LayoutParams.WRAP_CONTENT, WindowManager.LayoutParams.WRAP_CONTENT,
WindowManager.LayoutParams.TYPE_SYSTEM_OVERLAY,
WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE,
PixelFormat.OPAQUE);
mLayoutParam.gravity = Gravity.CENTER;
mLayoutParam.setTitle("AlertWindow from service");

// add and update
if(false == mTextView.isAttachedToWindow()) {
    mWm.addView(mTextView, mLayoutParam);
}
mTextView.setText("hello world");
mTextView.invalidate();

// remove
if(mTextView.isAttachedToWindow()) {
    mWm.removeView(mTextView);
}