Grid Layout 2x2 attempt equal sized, screen-filling attempt

GridLayoutSquares.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- REMEMBER TO UPDATE BOTH LANDSCAPE AND PORTRAIT FILES -->
    <LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:grid="http://schemas.android.com/apk/res-auto"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <!-- Setting up GridLayout support library in IntelliJ: http://stackoverflow.com/questions/12468606/intellij-and-android-support-v7-widget-gridlayout -->
    <android.support.v7.widget.GridLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            grid:columnCount="2"
            grid:rowCount="2"
            android:background="#FFF">
        <LinearLayout
                android:id="@+id/redSquare"
                android:layout_columnSpan="1"
                android:layout_rowSpan="1"
                android:background="#F00"
                grid:layout_row="0"
                grid:layout_column="0"
                android:layout_width="50dp"
                android:layout_height="50dp"
                />

        <LinearLayout
                android:id="@+id/greenSquare"
                android:layout_columnSpan="1"
                android:layout_rowSpan="1"
                android:background="#0F0"
                grid:layout_row="0"
                grid:layout_column="1"
                android:layout_width="50dp"
                android:layout_height="50dp"
                />
        <LinearLayout
                android:id="@+id/blueSquare"
                android:layout_columnSpan="1"
                android:layout_rowSpan="1"
                android:background="#00F"
                grid:layout_row="1"
                grid:layout_column="0"
                android:layout_width="50dp"
                android:layout_height="50dp"
                />


    </android.support.v7.widget.GridLayout>
</LinearLayout>

*********** make the GridLayout height and width as match_parent
***********and all the children layout height and width as wrap_content

<androidx.gridlayout.widget.GridLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
app:columnCount="2">

            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                app:layout_columnWeight="1"
                app:layout_rowWeight="1">>

                <Button
                    android:id="@+id/button16"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:text="Button" />
            </LinearLayout>
            />

            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                app:layout_columnWeight="1"
                app:layout_rowWeight="1">>

                <Button
                    android:id="@+id/button17"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:text="Button" />
            </LinearLayout>
            />

            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                app:layout_columnWeight="1"
                app:layout_rowWeight="1">>

                <Button
                    android:id="@+id/button18"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:text="Button" />
            </LinearLayout>
            />

            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                app:layout_columnWeight="1"
                app:layout_rowWeight="1">>

                <Button
                    android:id="@+id/button19"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:text="Button" />
            </LinearLayout>
            />

            <LinearLayout
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                app:layout_columnWeight="1"
                app:layout_rowWeight="1">>

                <Button
                    android:id="@+id/button20"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:text="Button" />
            </LinearLayout>
            />

        </androidx.gridlayout.widget.GridLayout>