Android 海拔属性不起作用

Question

Since upgrading to SDK 21 I've been trying to use the elevation property but it never seems to work.

I want to elevate a frame above others so I'm setting the following

android:elevation="4dp"

but there's no sign of shadow. I've tried buttons and framelayouts but not got any elevation

So here's the full tag

    <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:id="@+id/panel_card"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="#ffffff"
    android:elevation="4dp"
    >

Am I missing something else I need to add

Answer 1

确保包含 FrameLayout 的容器的背景不透明。

Answer 2

According to this Z = Elevation + TranslationZ

so try this:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:card_view="http://schemas.android.com/apk/res-auto"
  android:id="@+id/panel_card"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:background="#ffffff"
  android:elevation="4dp"
  android:translationZ="4dp">

Answer 3

You need to add a background to it something like:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:id="@+id/panel_card"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:elevation="4dp"
    android:background="@drawable/dialog_background">

Instead of using white color. Otherwise the shadows won't work. Also, is it not necessary to use android:translationZ attribute since that just adds to the elevation, but is not required if you don't want animation.