Android L Elevation Effect in Pre L (only using elevation property)

问题

I'm working on an App and want to have an elevation effect on ImageView or any View (!CardView in support library) in Pre L APIs. But i'm not able to achieve that what i tried is used android:elevation property but it doesn't have any effect (No elevation).

I can't find any API, if someone point out any documentation to achieve this in Pre L or any snippet from Support library is highly appreciated.

回答1:

If you want to set views in 3D shape, View.setElevation() and View.setTranslationZ() is a good idea.

But unfortunately, the two attributes and methods are introduced since Android API 21. So, you can't use them on pre-L or API 21- devices.

But, there is still a way to custom your views' shadows and outlines.

The bounds of a view's background drawable determine the default shape of its shadow. Outlines represent the outer shape of a graphics object and define the ripple area for touch feedback.

Consider this view, defined with a background drawable:

<TextView
android:id="@+id/myview"
...
android:elevation="2dp"
android:background="@drawable/myrect" />

The background drawable is defined as a rectangle with rounded corners:

<!-- res/drawable/myrect.xml -->
<shape xmlns:android="http://schemas.android.com/apk/res/android"
       android:shape="rectangle">
    <solid android:color="#42000000" />
    <corners android:radius="5dp" />
</shape>

The view casts a shadow with rounded corners, since the background drawable defines the view's outline. Providing a custom outline overrides the default shape of a view's shadow.

To define a custom outline for a view in your code:

1. Extend the ViewOutlineProvider class.
2. Override the getOutline() method.
3. Assign the new outline provider to your view with the View.setOutlineProvider() method.

You can create oval and rectangular outlines with rounded corners using the methods in the Outline class. The default outline provider for views obtains the outline from the view's background. To prevent a view from casting a shadow, set its outline provider to null.

Hopefully it helps.

P.S.: yourAppNs:elevation="4dp" will be a good idea if you are using android-design-library.

回答2:

• ViewCompat.setElevation()/getElevation() doesnt work on pre Lollipop.
• There isnt anything worth checking out at the support library, at least until version 21.1.1
• As for creating an elevation effect by yourself take a look at this

来源：https://stackoverflow.com/questions/26468087/android-l-elevation-effect-in-pre-l-only-using-elevation-property