How can I emulate button height (shadow) in Android API below 21?

Question

I have this minimal Android Studio project in just one button. I assign a shadow to the button with:

android:elevation="3dp" android:translationZ="3dp" android:stateListAnimator="@null" 

and I see a shadow on the Android Studio Design tab. But I also get a warning in the xml editor

The attribute ... is used only in API level 21 and higher (current min is 16)

Indeed, the shadow of the button is displayed only in emulators with API level 21 or higher , and it is displayed flat, with no shadow at all in emulators with API level lower than 21 .

So, the specific question is: how can I emulate the shadow effect in API lower than 21 .

activity_main.xml

 <?xml version="1.0" encoding="utf-8"?> <ScrollView xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" xmlns:app="http://schemas.android.com/apk/res-auto"> <LinearLayout android:id="@+id/main_layout" android:layout_width="wrap_content" android:layout_height="wrap_content" android:weightSum="1"> <RelativeLayout android:layout_width="match_parent" android:layout_height="match_parent" android:layout_margin="20dp" android:layout_weight="2.24"> <Button android:id="@+id/my_button" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerHorizontal="true" android:layout_marginLeft="20dp" android:layout_marginBottom="20dp" android:elevation="5dp" android:translationZ="5dp" android:stateListAnimator="@null" android:background="@android:color/holo_green_light" android:text="BUTTON"/> </RelativeLayout> </LinearLayout> </ScrollView> 

MainActivity.java

 public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } } 

Button showing a shadow in API 22 :

The same button does not show a shadow, in API 16 :

Answer 1

For the Pre-LolliPop you need to create a shadow or elevation using a Pre-LolliPop file. In this way.

Create a drawable file in your folder e.g. element_background.xml

 <?xml version="1.0" encoding="utf-8"?> <layer-list xmlns:android="http://schemas.android.com/apk/res/android"> <item> <shape android:shape="rectangle"> <solid android:color="#BDBDBD"/> <corners android:radius="5dp"/> </shape> </item> <item android:left="0dp" android:right="0dp" android:top="0dp" android:bottom="2dp"> <shape android:shape="rectangle"> <solid android:color="#ffffff"/> <corners android:radius="5dp"/> </shape> </item> </layer-list> 

Then add the following code to the item you want.

 android:background="@drawable/element_background" 

Answer 2

If you want, you can try Carbon. This material for backporting for the library goes back to 2.2. It supports enhancement and generated animated shadows.

https://github.com/ZieIony/Carbon