Android XML: Centring a view in relative layout- android:layout_centerHorizontal="true" not working?

Question

I am trying to center the bottom view ( android:id="@+id/tvStroopCountdown" ) in my XML layout using android:layout_centerHorizontal="true".

However it is not working, instead it is positioned to the left on the screen.

Why not, and how can I solve this?

Full XML:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="@drawable/menubackground"
    >

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

        <TextView
            android:id="@+id/tvStroopColor"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:paddingBottom="3dp"
            android:layout_marginTop="11dp"
             android:layout_marginBottom="15dp"
            android:text="  "
            android:textSize="50dp" 
            android:background="#ffffff"/>
    </LinearLayout>

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:gravity="center" >

        <Button
            android:id="@+id/btnStroop1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text=" " 
            android:textSize="40dp"
            />

        <Button
            android:id="@+id/btnStroop2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text=" " 
            android:textSize="40dp"
            />
    </LinearLayout>

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical" >

        <TextView
            android:id="@+id/tvStroopResults"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:paddingBottom="3dp"
            android:text="  "
            android:layout_centerHorizontal="true"
            android:textSize="35dp" />

        <TextView
            android:id="@+id/tvStroopScore"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/tvStroopResults"
            android:layout_centerHorizontal="true"
            android:paddingBottom="3dp"
            android:text=" "
            android:textSize="35dp" />

        <TextView
            android:id="@+id/tvStroopSeeMeditation"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/tvStroopScore"
            android:layout_centerHorizontal="true"
            android:paddingBottom="3dp"
            android:text=" "
            android:textSize="35dp" />

        <TextView
            android:id="@+id/tvStroopSeeAttention"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/tvStroopSeeMeditation"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="4dp"
            android:text=" "
            android:textSize="35dp" />

        <TextView
            android:id="@+id/tvStroopCountdown"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_below="@+id/tvStroopSeeAttention"
            android:layout_centerHorizontal="true"
            android:ems="10"
            android:textSize="30dp" 
            android:hint=" " >
        </TextView>
    </RelativeLayout>

</LinearLayout>

Answer 1

Change android:layout_centerHorizontal="true" to android:gravity="center_horizontal". What you've written centres the TextView within the RelativeLayout, but displays the text at the left of the TextView. This won't work because your TextView has the same width as the RelativeLayout because you used fill_parent.