Why can't I center a button across two columns of an Android GridLayout?

Question

I am trying to create a static GridLayout with two rows and two columns. In the bottom row, a button should be centered across the two columns. Instead, the button seems to be centered only within the right column:

(I stretched the button's height so the asymmetry would be more obvious.)

I expected these attributes within the Button element to center it across the two columns:

        android:layout_column="0"
        android:layout_columnSpan="2"
        android:layout_gravity="center_horizontal"

Here is my complete layout:

<?xml version="1.0" encoding="utf-8"?>
<GridLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:columnCount="2"
    android:rowCount="2">
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_row="0"
        android:layout_column="0"
        android:text="Title: " />
    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_row="0"
        android:layout_column="1"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="fill_parent"
        android:text="@string/search"
        android:layout_row="1"
        android:layout_column="0"
        android:layout_columnSpan="2"
        android:layout_gravity="center_horizontal"/>
</GridLayout>

How can I center an element across multiple columns?

Answer 1

Previous answer looks fine to me, but alternatively you can enclose the button in a linear layout, something like:

<?xml version="1.0" encoding="utf-8"?>
<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:columnCount="2"
    android:rowCount="2">


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_column="0"
        android:layout_row="0"
        android:text="Title: " />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_column="1"
        android:layout_row="0"
        android:text="hello world" />

    <LinearLayout
        android:orientation="vertical"
        android:layout_column="0"
        android:layout_row="1"
        android:layout_columnSpan="2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <Button android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="test buttontest buttontest button"
            android:layout_gravity="center_horizontal"
            android:layout_weight="1" />
    </LinearLayout>

</GridLayout>

This should do what you aim to:

Answer 2

Try this

<?xml version="1.0" encoding="utf-8"?>

<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:columnCount="2"
android:rowCount="2">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_column="0"
    android:layout_row="0"
    android:text="Title: " />

<EditText
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_column="1"
    android:layout_row="0"
    android:text="hello world" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_column="0"
    android:layout_columnSpan="2"
    android:layout_gravity="center_vertical|center_horizontal"
    android:layout_row="1"
    android:text="search" /></GridLayout>