Setting Elevation in XML on AppCompat CardView on

问题:

From what I understand, early in the preview stage there seemed to be no way to set elevation in XML only on CardViews without a hack in Java. Now that the official release is out, is there any way of doing this in XML without writing Java code to set elevation?

I have tried card_view:cardElevation to no effect. I had thought when I was using the emulators for 5.0 everything was fine. But now that I'm using the official version on my actual device all of my CardViews disappeared

Pre Lollipop, it works great.

Here is my full xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:id="@+id/cv1"
    card_view:cardElevation="4dp"
    android:layout_margin="6dp"
    card_view:cardCornerRadius="3dp"
    android:layout_height="match_parent">

回答1:

It looks like a margin/padding problem, try to set the cardUseCompatPadding attribute to true. E.g.:

<android.support.v7.widget.CardView 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_margin="6dp"
    card_view:cardUseCompatPadding="true"
    card_view:cardElevation="4dp"
    card_view:cardCornerRadius="3dp">

Explanation from Android doc :

CardView adds additional padding to draw shadows on platforms before L.

This may cause Cards to have different sizes between L and before L. If you need to align CardView with other Views, you may need api version specific dimension resources to account for the changes. As an alternative, you can set cardUseCompatPadding flag to true and CardView will add the same padding values on platforms L and after.

Since setting cardUseCompatPadding flag to true adds unnecessary gaps in the UI, default value is false.

回答2:

You have to use the cardElevation attribute

<android.support.v7.widget.CardView
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    card_view:cardElevation="4dp" />

回答3:

If you have this line

android:hardwareAccelerated="false"

in manifest application tag your shadows were not displayed. try to remove this line

or use

android:hardwareAccelerated="true"

This worked for me! I hope it works for you too :)

回答4:

It solved me by adding

xmlns:card_view="http://schemas.android.com/apk/res-auto"

for example:

<android.support.v7.widget.CardView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginTop="5dp"
    android:layout_marginLeft="5dp"
    android:layout_marginRight="5dp"
    card_view:cardCornerRadius="5dp">