工具栏没有阴影，即使添加了应用栏布局

Question

我的工具栏没有任何阴影。大多数解决方案建议我将工具栏包装在 AppBarLayout 中，当我尝试这样做时，即使这样我也不会得到任何阴影。为什么即使我有 AppBarLayout，我也不会得到任何阴影，我该如何解决这个问题。

我不想要通过在工具栏下添加视图来阴影，有没有其他稳定的方法来实现阴影。

这是我的整个xml布局，它有工具栏：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:orientation="vertical"
   app:layout_scrollFlags="scroll|enterAlways|snap|exitUntilCollapsed">
   <android.support.design.widget.AppBarLayout
     android:id="@+id/appbar"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     android:theme="@style/AppTheme.AppBarOverlay"
     app:elevation="4dp"
     app:layout_constraintLeft_toLeftOf="parent"
     app:layout_constraintRight_toRightOf="parent"
     app:layout_constraintTop_toTopOf="parent">
    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="@drawable/ab_gradient"
        app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<ScrollView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:scrollbars="vertical"
    app:layout_constraintTop_toBottomOf="@id/appbar">
    <android.support.constraint.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="10dp"
        android:layout_marginRight="10dp"
        app:layout_scrollFlags="scroll|enterAlways|snap|exitUntilCollapsed">
        <TextView
            android:id="@+id/textViewProfilePhotoLabel"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:padding="10dp"
            android:text="@string/profile_photo_label"
            android:textColor="@android:color/black"
            android:textSize="16sp"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
        <FrameLayout
            android:id="@+id/frameLayout"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:elevation="6dp"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@id/textViewProfilePhotoLabel">
            <de.hdodenhof.circleimageview.CircleImageView
                android:id="@+id/circleImageViewProfilePhoto"
                android:layout_width="140dp"
                android:layout_height="140dp"
                android:src="@color/colorBlack"
                app:civ_border_color="#ffffff"
                app:civ_border_width="3dp" />
            <ImageView
                android:id="@+id/imageViewEditProfilePhoto"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="bottom|end"
                android:src="@drawable/ic_edit_black_24dp" />
        </FrameLayout>
        <android.support.design.widget.TextInputLayout
            android:id="@+id/textInputLayoutUsersFirstName"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginTop="20dp"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@id/frameLayout">
            <android.support.design.widget.TextInputEditText
                android:id="@+id/editTextUsersFirstName"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/users_first_name_label"
                android:textSize="16sp" />
        </android.support.design.widget.TextInputLayout>
        <android.support.design.widget.TextInputLayout
            android:id="@+id/textInputLayoutUsersLastName"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@id/textInputLayoutUsersFirstName">
            <android.support.design.widget.TextInputEditText
                android:id="@+id/editTextUsersLastName"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/users_last_name_label"
                android:textSize="16sp" />
        </android.support.design.widget.TextInputLayout>
        <android.support.design.widget.TextInputLayout
            android:id="@+id/textInputLayoutProfileHeadline"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@id/textInputLayoutUsersLastName">
            <EditText
                android:id="@+id/editTextProfileHeadline"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/users_tagline_label"
                android:textSize="16sp" />
        </android.support.design.widget.TextInputLayout>
        <android.support.design.widget.TextInputLayout
            android:id="@+id/textInputLayoutUsersEducation"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:visibility="gone"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@id/textInputLayoutProfileHeadline">
            <EditText
                android:id="@+id/editTextUsersEducation"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/users_Education_label"
                android:textSize="16sp" />
        </android.support.design.widget.TextInputLayout>
        <android.support.design.widget.TextInputLayout
            android:id="@+id/textInputLayoutUsersProfession"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@id/textInputLayoutUsersEducation">
            <EditText
                android:id="@+id/editTextUsersProfession"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/users_profession_label"
                android:textSize="16sp" />
        </android.support.design.widget.TextInputLayout>
        <android.support.design.widget.TextInputLayout
            android:id="@+id/textInputLayoutUsersLocation"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@id/textInputLayoutUsersProfession">
            <EditText
                android:id="@+id/editTextUsersLocation"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/users_location_label"
                android:textSize="16sp" />
        </android.support.design.widget.TextInputLayout>
        <android.support.design.widget.TextInputLayout
            android:id="@+id/textInputLayoutUsersBio"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toBottomOf="@id/textInputLayoutUsersLocation">
            <EditText
                android:id="@+id/editTextUsersBio"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:hint="@string/users_about_me_label"
                android:inputType="textAutoCorrect"
                android:textSize="16sp" />
        </android.support.design.widget.TextInputLayout>
    </android.support.constraint.ConstraintLayout>
</ScrollView>
</LinearLayout>

工具栏中使用的样式：

 <style name="AppTheme.AppBarOverlay" parent="ThemeOverlay.AppCompat.Dark.ActionBar" />
<style name="AppTheme.PopupOverlay" parent="ThemeOverlay.AppCompat.Light" />

为什么我没有影子，我该如何解决这个问题？

提前谢谢。

Answer 1

将elevation和marginBottom添加到工具栏，如下所示：

<android.support.v7.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:background="@drawable/ab_gradient"
    android:elevation="4dp"
    android:marginBottom="4dp"
    app:popupTheme="@style/AppTheme.PopupOverlay" />