问当没有图像时，CollapsingToolbarLayout不显示标题

EN

<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"
>

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/AppTheme.AppBarOverlay">
    <android.support.design.widget.CollapsingToolbarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:fitsSystemWindows="true"
        app:contentScrim="?attr/colorPrimary"
        app:expandedTitleMarginStart="40dp"
        android:background="@color/transparent"
        app:layout_scrollFlags="scroll|exitUntilCollapsed">
        <ImageView
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:scaleType="centerCrop"
            android:fitsSystemWindows="true"                
            app:layout_collapseMode="parallax"/>
        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/transparent"
            app:layout_collapseMode="pin"
            app:popupTheme="@style/AppTheme.PopupOverlay"
            />

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


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

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