使用android:elevation在LinearLayout顶部投射阴影 [英] Cast shadow on top of LinearLayout using android:elevation

问题描述

我有这个LinearLayout，它将被放置在活动布局的底部.我希望此LinearLayout具有4dp高程，就像顶部工具栏应该具有的那样，但是，由于android:elevation将阴影放置在ui组件下方，并且此特定组件(linearLayout)将位于屏幕底部，我根本看不到任何海拔.

I have this LinearLayout that is going to be placed on the bottom of an activity layout. I want this LinearLayout to have a 4dp elevation, just like the top toolbar should have, however, since android:elevation places the shadow below the ui component and this specific component (linearLayout) is going to be on the bottom of the screen, I won't see any elevation at all..

这是我的LinearLayout代码，并带有实现默认高程的图像:

This is my LinearLayout code, and an image of it with the default elevation implemented:

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:weightSum="3"
    android:background="@android:color/transparent"
    android:orientation="horizontal"
    android:elevation="4dp"
    android:layout_alignParentBottom="true">

    <ImageButton
        android:id="@+id/playButton"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:scaleType="center"
        android:clickable="true"
        android:background="@drawable/bottom_toolbar_menu_selector"
        android:src="@drawable/ic_play"
        style="?android:attr/borderlessButtonStyle" />

    <ImageButton
        android:id="@+id/stopButton"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:scaleType="center"
        android:clickable="true"
        android:background="@drawable/bottom_toolbar_menu_selector"
        android:src="@drawable/ic_stop"
        style="?android:attr/borderlessButtonStyle" />

    <ImageButton
        android:id="@+id/bookmarkButton"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:scaleType="center"
        android:clickable="true"
        android:background="@drawable/bottom_toolbar_menu_selector"
        android:src="@drawable/ic_bookmark"
        style="?android:attr/borderlessButtonStyle" />

</LinearLayout>

是否可以使用elevation在ui组件顶部放置阴影? 预先感谢！

Is there a way, using elevation to place a shadow on top of the ui component? Thanks in advance!

推荐答案

从理论上讲，您无法选择android:elevation进行此操作，因为您无法选择要投射阴影的方向.

You can't theoretically do it with android:elevation, in the sense that you can't choose the direction where the shadow is going to be cast.

有两种解决方案.

1.可绘制对象

例如，您可以在布局的正上方放置ImageView并设置android:src="@drawable/shadow".这应该是XML中定义的垂直GradientDrawable，如

You could, for instance, put an ImageView right above your layout and set android:src="@drawable/shadow". This should be a vertical GradientDrawable defined in XML, as explained here.

2.解决方法

虽然大多数阴影实际上在视图下方，但微妙的阴影也在上方.一种解决方法可能是对elevation使用非常高的值，例如40dp:由于布局的原因，底部将被隐藏，而顶部将被扩展并看起来像一个普通的阴影.

While most of the shadow is actually below the view, a subtle shadow is also above. A workaround might be using a very high value for elevation, like 40dp: the bottom part is going to be hidden due to your layout, while the top is going to be expanded and look like a common shadow.

在任何一种情况下，您都无法控制dp中的高程值，因为您无法确定阴影是否等同于android:elevation=4dp投射的阴影.

In either case, you do not have control over the elevation value in dp, in the sense that you can't be sure your shadow is equivalent to the one cast by android:elevation=4dp.

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