How to place application elements from the center?

Question

Android

Centering the text input form and trying to place another form at the bottom and one at the top. But they move up, what's the problem?

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fillViewport="true"
    android:scrollbars="vertical" >

    <RelativeLayout xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="640dp"
        android:paddingBottom="@dimen/activity_vertical_margin"
        android:paddingLeft="@dimen/activity_horizontal_margin"
        android:paddingRight="@dimen/activity_horizontal_margin"
        android:paddingTop="@dimen/activity_vertical_margin"
        tools:context=".activity.MainActivity"
        android:background="#ffffff">


        <EditText
            android:layout_width="300dp"
            android:layout_height="wrap_content"
            android:id="@+id/editText"
            android:layout_centerVertical="true"
            android:layout_centerHorizontal="true" />

        <EditText
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/editText2"
            android:layout_below="@+id/editText"
            android:layout_marginTop="70dp"
            android:layout_alignLeft="@+id/editText"
            android:layout_alignStart="@+id/editText"
            android:layout_alignRight="@+id/editText"
            android:layout_alignEnd="@+id/editText" />

        <EditText
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/editText3"
            android:layout_above="@+id/editText"
            android:layout_marginTop="70dp"
            android:layout_alignLeft="@+id/editText2"
            android:layout_alignStart="@+id/editText2"
            android:layout_alignRight="@+id/editText2"
            android:layout_alignEnd="@+id/editText2" />
    </RelativeLayout>

</ScrollView>

Answer 1

If I put three EditTexts in the center, then it turned out like this for me ....

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.centeractivity.MainActivity" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:orientation="vertical" >

        <EditText
            android:id="@+id/editText1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:ems="10" >

            <requestFocus />
        </EditText>

        <EditText
            android:id="@+id/editText3"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:ems="10" />

        <EditText
            android:id="@+id/editText2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:ems="10" />

    </LinearLayout>
</RelativeLayout>

Answer 2

LinearLayout with orientation=vertical and gravity=center will save you