Estou usando umSwipeRefreshLayout para atualizar o conteúdo.

O problema é que ele está funcionando, mas não é visível enquanto desliza para baixo.

Aqui está como eu tenhoSwipeRefreshLayout no arquivo xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="com.abc.xyz.MainActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay"/>

    </android.support.design.widget.AppBarLayout>

    <android.support.v4.widget.SwipeRefreshLayout
        android:id="@+id/swipetorefresh"
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        xmlns:android="http://schemas.android.com/apk/res/android">

    <include layout="@layout/content_main"/>

    </android.support.v4.widget.SwipeRefreshLayout>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        android:src="@drawable/ic_add_white_24dp"/>

</android.support.design.widget.CoordinatorLayout>

Aqui está écontent_main.xml código do arquivo:

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

<RelativeLayout
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.abc.xyz.MainActivity"
    tools:showIn="@layout/app_bar_main">

    <TextView
        android:id="@+id/main_txt1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="xxx"
        android:textSize="17sp"/>

    <TextView
        android:id="@+id/main_txt2"
        android:layout_below="@+id/main_txt1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dp"
        android:text="xxx"
        android:textStyle="bold"
        android:textSize="17sp"/>

    <TextView
        android:id="@+id/main_txt3"
        android:layout_below="@+id/main_txt2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="xxx"
        android:textSize="16sp"/>

    <TextView
        android:id="@+id/main_txt4"
        android:layout_below="@+id/main_txt3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dp"
        android:text="xxx"
        android:textStyle="bold"
        android:textSize="17sp"/>

    <TextView
        android:id="@+id/main_txt_swipetorefresh"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="xxx"
        android:layout_centerInParent="true"
        android:gravity="center_horizontal|center_vertical"/>

    <TextView
        android:id="@+id/main_txt5"
        android:layout_below="@+id/main_txt4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="xxx"
        android:textSize="16sp"/>

    <TextView
        android:id="@+id/main_txt6"
        android:layout_below="@+id/main_txt5"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dp"
        android:text="xxx"
        android:textStyle="bold"
        android:textSize="17sp"/>

    <TextView
        android:id="@+id/main_txt7"
        android:layout_below="@+id/main_txt6"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="xxx"
        android:textSize="16sp"/>

</RelativeLayout>

Veja como está no arquivo java:

swipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.swipetorefresh);
        swipeRefreshLayout.setColorSchemeColors(Color.parseColor("#00BCD4"), Color.parseColor("#FF9800"), Color.parseColor("#339a60"));
        swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {

                swipeRefreshLayout.setRefreshing(true);

            }
        });

Por favor, deixe-me saber o que está acontecendo de errado aqui?

Desculpe, se a pergunta parece estar mal formatada. Eu ainda sou iniciante.