Android Studio Layout Editor: How do I center these views in the middle of this Layout - android-relativelayout

Question

In the screenshot, you can see I've drawn in red arrows indicating that I want to shift the widgets to the right a bit. In other words, I want to center things, and yet I'm having difficulty.
Below is the XML:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/linearLayout1"
android:layout_width="wrap_content"
android:layout_height="fill_parent"
android:orientation="vertical">
<DatePicker
android:id="#+id/datePicker"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:calendarViewShown="false"
android:layout_alignParentTop="true" android:layout_alignParentStart="true"
>
</DatePicker>
<TimePicker
android:id="#+id/timePicker"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/datePicker" android:layout_alignParentStart="true">
</TimePicker>
<Button
android:id="#+id/btnSave"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="25sp"
android:text="#string/ok"
android:layout_below="#+id/timePicker" android:layout_alignParentStart="true"
android:layout_alignEnd="#+id/timePicker"/>
</RelativeLayout>

Answer 1

You can add android:layout_centerHorizontal="true" to all he widgets you want to center horizontally.
Also I suggest you change the linearLayout1's width and height to match_parent. fill_parent, which is value of layout_height is deprecated long time ago, and in order to center your widgets horizontally on the screen, you need your layout to match the screen bounds.