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android - how to put shadow on just the top edge of rounded cardview?

[![my image][1]][1]
As. you can see from the image i have a rounded corner shape ..but i want to have a shadow just on the top (there is no where else for it anyway since its covered on the other ends). How can i place a shadow just at the top of this cardView ? here is what i have so far and i've tried using two framelayouts earlier.
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/viewRoot"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<com.google.android.material.card.MaterialCardView
android:theme="#style/Theme.MaterialComponents.Light"
android:id="#+id/greenCardView"
android:layout_width="match_parent"
android:layout_height="100dp"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:cardCornerRadius="16dp"
app:cardElevation="0dp"
android:clipToOutline="true"
android:clipToPadding="true"
android:clipChildren="true"
app:cardPreventCornerOverlap="true"
app:cardBackgroundColor="#color/green">
<androidx.constraintlayout.widget.ConstraintLayout
android:id="#+id/contentContainer"
android:layout_width="match_parent"
android:background="#color/transparent"
android:layout_height="54dp"/>
</androidx.constraintlayout.widget.ConstraintLayout>
i also need the shadow to have no background under it ..so it should not be on a white background, i just want the shadow on top alone on a transparent background.
update: after i udated to 70dp elevation the shadow is only appearing on the bottom :
[![enter image description here][2]][2]
notice the shadow is only appearing at the bottom . how can i make shadow just at the top
[1]: https://i.stack.imgur.com/8XC6l.png
[2]: https://i.stack.imgur.com/egRoB.png

Increse the value of
app:cardElevation="0dp"

it was how i was attaching the scrollview to the cardview ..i used a space view to attach it a bit lower and it works great now (since i dont have access to negative margins) ..thanks
what i learned is that when you have a scrollview attached to a cardview then you should attach the scrollview a few pixels away from the top so that it does not look cut off when it scrolls.

Inconsistent shadow on MaterialCardView when its overlaid by children

When a child of a MaterialCardView fully overlays it, the shadow under it disappears. I have tried setting elevation to the view itself but to no effect.
Example layout:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<!-- Elevation of this card is large for demonstration purposes -->
<com.google.android.material.card.MaterialCardView
android:layout_width="match_parent"
android:layout_height="90dp"
android:layout_margin="16dp"
app:cardElevation="24dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
<View
android:layout_width="120dp"
android:layout_height="match_parent"
android:background="#color/purple_500"
android:elevation="24dp"
app:elevation="24dp" />
</com.google.android.material.card.MaterialCardView>
</androidx.constraintlayout.widget.ConstraintLayout>
Screenshot of the problem:
Here shadow is clearly visible under white background of the card, but not under purple view.
The app was tested on API 30 emulator, but I have observed similar behaviour on API 29 physical device.

Ok it turns out that it was just an optical illusion: if you overlay the purple control in Paint the shadow is consistent:
Now its up to me how to prevent the following illusion from impacting the visual experience of my app.

Cardview shadow looks different when inside a ScrollView

I stumbled upon something weird. I am using the same CardView component in more than one place in my app, all with the same elevation (3dp), and they all looks the same. However, for one scenario I need to embed the CardView inside a ScrollView. I didn't change anything in the CardView configuration, but the shadow now looks different.
This is my layout:
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipChildren="false"
android:clipToPadding="false"
android:padding="16dp"
android:scrollbars="none">
<androidx.cardview.widget.CardView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:clipChildren="false"
android:clipToPadding="false"
app:cardCornerRadius="8dp"
app:cardElevation="3dp"
app:cardUseCompatPadding="true">
<!-- some other views-->
</androidx.cardview.widget.CardView>
</ScrollView>
In the picture below you can see on the right the CardView and on the left the two shadows: on the top the shadow generated by the CardView alone, on the bottom the one generated when the CardView is inside a ScrollView. As you can see the second one appears darker and thicker.
NOTE: The background color (#FAFAFA) is the same in both scenario.

For both cases, I would check the following properties as it could contribute to the difference you're seeing:
getTranslationZ()
getElevation()
getOutlineAmbientShadowColor() (this is only valid in API 28+)
getOutlineSpotShadowColor() (this is only valid in API 28+)
Plus, checking Layout inspector to see if there's any view that could affect to the rendering.
Also, this article from Sebastiano Poggi could be of help.

Android Camera2Video Preview Issue

I am using Google's API Camera2Video classes Camera2VideoFragment and AutoFitTextureView and I have a small problem. When I'm using the preview in a custom FrameLayout, it goes to the left corner.
I have found a way to sretch the preview for it to fill the whole framelayout but as expected, it looks way too stretched. Perfect solution would be if there could be some black edges on corners and the screen would be in the middle. Also I dont think making the inflator to inflate the layout from the middle would help because there could be cases where the screen is big enough for the preview to fit properly and that being positioned in the middle would just ruin it.
Link to Google's Camera2Video API: https://github.com/googlesamples/android-Camera2Video
I created a simple layout to show what I get. (This is the only thing I have changed after downloading Google's API, and also removing the buttons that came with):
The XML:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="250dp"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:background="#000"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:context="com.example.android.camera2basic.CameraActivity" />
</android.support.constraint.ConstraintLayout>
And a picture of what I'm seeing.

You are using a sample that wraps the AutoFitTextureView in an extra wrapper of RelativeLayout. There it defines the position of the texture view as
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
which caused the layout that you observed.
Your task does not need this wrapper. You can embed the AutoFitTextureView directly inside the FrameLayout of CameraActivity. Your FrameLayout should define
android:gravity="center"
to command the children to be centered.
Note that you can probably remove the wrapping ConstrantLayout, if its only child is the id/container FrameLayout.

Cardview - white border around card

I am using a cardview as the root of a custom view I am writing. I using the v7 support library. My XML looks like this:
<?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:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_marginRight="6dp"
card_view:cardElevation="0dp">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<!-- some other views -->
</LinearLayout>
</android.support.v7.widget.CardView>
My problem is that I am getting a white border around my card view. It looks like it is there to indicate elevation as it is thicker on the right side. I've tried adjusting cardElevation and MaxCardElevation in my XML like so :
card_view:cardElevation="0dp"
and in code in my custom view that extends CardView and uses this layout:
setCardElevation(0);
setMaxCardElevation(0);
But the white border persists. I'm not sure how to get rid of it. If anyone had any input into why this is happening or suggestions on how I can remove the white border it would be appreciated. Thanks much.

I know it's a bit late, but for anyone having a similar problem:
I had the same issue: A white border was shown on pre-lollipop devices.
I solved it setting the cardPreventCornerOverlap to false on your XML.
Like this:
<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="wrap_content"
android:layout_height="match_parent"
android:layout_marginRight="6dp"
card_view:cardPreventCornerOverlap="false">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<!-- some other views -->
</LinearLayout>
</android.support.v7.widget.CardView>

Support CardView doesn't support content clipping, because it's expensive on older devices. It's possible to clip content using Canvas.saveLayer/restoreLayer and PorterDuff modes. This is how Carbon implements rounded corners with correct content clipping. See the image:

I might be late in the game, but I had the same issue. Just wanted to share a simple solution!
My custom view extended a CardView and I had a margin applied to the root element (i.e. CardView) in the XML just like in the original question. This ended up giving me the extra white border like this:
Solution was to move the margin from root of the Custom View XML to the declaration of your custom view (check comments in the snippet)
Code snippet:
<android.support.v7.widget.CardView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="#+id/cvSettings"
style="#style/DefaultCardViewStyle"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="#dimen/default_margin" <!-- Remove this -->
app:cardElevation="#dimen/default_card_elevation">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
.
.
.
</android.support.v7.widget.CardView>
Ended up just moving over the margin to my custom view declaration which got rid of the extra white border:
<com.example.android.custom.MyCustomView
android:id="#+id/custom_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="#dimen/default_margin" <!-- Move it here-->
cv:pt_widgetColor="#color/colorAccent" />
After the change, much cleaner :) :

use cardBackgroundColor="color" in xml card_view
sample code :
<android.support.v7.widget.CardView
android:id="#+id/card_view_khaterat"
android:layout_width="250dp"
android:layout_height="100dp"
android:layout_gravity="center_horizontal"
app:cardBackgroundColor="#f56f6c"/>