Round corner for BottomSheetDialogFragment

I have a custom BttomSheetDialogFragment and I want to have round corners in top of Bottom View

This is my Custom class that inflates my layout that I want to appear from bottom

View mView;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    mView = inflater.inflate(R.layout.charge_layout, container, false);
    initChargeLayoutViews();
    return mView;
}

and also I have this XML resource file as background:

<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle"
    >
    <corners android:topRightRadius="35dp"
        android:topLeftRadius="35dp"
        />
    <solid android:color="@color/white"/>

    <padding android:top="10dp"
        android:bottom="10dp"
        android:right="16dp"
        android:left="16dp"/>
</shape>

The problem is, when I set this resource file as background of my Layout's root element, the corners still are not rounded.

I can't use below code:

this.getDialog().getWindow().setBackgroundDrawableResource(R.drawable.charge_layout_background);

Because it overrides the default background of BottomSheetDialog and there won't be any semi-transparent gray color above my Bottom View.

Create a custom drawable rounded_dialog.xml:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <solid android:color="@android:color/white"/>
    <corners android:topLeftRadius="16dp"
        android:topRightRadius="16dp"/>

</shape>

Then override bottomSheetDialogTheme on styles.xml using the drawable as background:

<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">       
    <item name="bottomSheetDialogTheme">@style/AppBottomSheetDialogTheme</item>
</style>

<style name="AppBottomSheetDialogTheme"
    parent="Theme.Design.Light.BottomSheetDialog">
    <item name="bottomSheetStyle">@style/AppModalStyle</item>
</style>

<style name="AppModalStyle"
    parent="Widget.Design.BottomSheet.Modal">
    <item name="android:background">@drawable/rounded_dialog</item>
</style>

This will change all the BottomSheetDialogs of your app.

With the new Material Component library you can customize the shape of your component using the shapeAppearanceOverlay attribute in your style (Note: it requires at least the version 1.1.0)

Just use the BottomSheetDialogFragment overriding the onCreateView method and then define your custom style for Bottom Sheet Dialogs.

Define the bottomSheetDialogTheme attribute in styles.xml in your app theme:

  <!-- Base application theme. -->
  <style name="AppTheme" parent="Theme.MaterialComponents.Light">
    <!-- Customize your theme here. -->
    <item name="colorPrimary">@color/colorPrimary</item>
    ....
    <item name="bottomSheetDialogTheme">@style/CustomBottomSheetDialog</item>
  </style>

Then just define your favorite shape with shapeAppearanceOverlay

  <style name="CustomBottomSheetDialog" parent="@style/ThemeOverlay.MaterialComponents.BottomSheetDialog">
    <item name="bottomSheetStyle">@style/CustomBottomSheet</item>
  </style>

  <style name="CustomBottomSheet" parent="Widget.MaterialComponents.BottomSheet">
    <item name="shapeAppearanceOverlay">@style/CustomShapeAppearanceBottomSheetDialog</item>
  </style>

  <style name="CustomShapeAppearanceBottomSheetDialog" parent="">
    <item name="cornerFamily">rounded</item>
    <item name="cornerSizeTopRight">16dp</item>
    <item name="cornerSizeTopLeft">16dp</item>
    <item name="cornerSizeBottomRight">0dp</item>
    <item name="cornerSizeBottomLeft">0dp</item>
  </style>

---

You can obtain the same behavior overriding this method in your BottomSheetDialogFragment (instead of adding the bottomSheetDialogTheme in your app theme):

@Override public int getTheme() {
    return R.style.CustomBottomSheetDialog;
  }

In this case you are using this themeOverlay only in the single BottomSheetDialogFragment and not in all the app.

---

Important note about the EXPANDED STATE:

In the expanded state the BottomSheet has flat corners . You can check the official comment in github repo: >Our design team is strongly opinionated that rounded corners indicate scrollable content while flat corners indicate that there is no additional content. As such, they do no want us to add this change with fitToContents.

This behavior is provided by the BottomSheetBehavior and it is impossible to override it.
However there is a workaround -> DISCLAIMER: it can stop to work in the next releases !!

You can add a BottomSheetCallback in the BottomSheetDialogFragment:

  @NonNull @Override public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
    Dialog dialog = super.onCreateDialog(savedInstanceState);


    ((BottomSheetDialog)dialog).getBehavior().addBottomSheetCallback(new BottomSheetBehavior.BottomSheetCallback() {

      @Override public void onStateChanged(@NonNull View bottomSheet, int newState) {
        if (newState == BottomSheetBehavior.STATE_EXPANDED) {
          //In the EXPANDED STATE apply a new MaterialShapeDrawable with rounded cornes
          MaterialShapeDrawable newMaterialShapeDrawable = createMaterialShapeDrawable(bottomSheet);
          ViewCompat.setBackground(bottomSheet, newMaterialShapeDrawable);
        }
      }

      @Override public void onSlide(@NonNull View bottomSheet, float slideOffset) {

      }
    });

    return dialog;
  }

  @NotNull private MaterialShapeDrawable createMaterialShapeDrawable(@NonNull View bottomSheet) {
    ShapeAppearanceModel shapeAppearanceModel =

      //Create a ShapeAppearanceModel with the same shapeAppearanceOverlay used in the style
      ShapeAppearanceModel.builder(getContext(), 0, R.style.CustomShapeAppearanceBottomSheetDialog)
        .build();

      //Create a new MaterialShapeDrawable (you can't use the original MaterialShapeDrawable in the BottoSheet)
      MaterialShapeDrawable currentMaterialShapeDrawable = (MaterialShapeDrawable) bottomSheet.getBackground();
      MaterialShapeDrawable newMaterialShapeDrawable = new MaterialShapeDrawable((shapeAppearanceModel));
      //Copy the attributes in the new MaterialShapeDrawable
      newMaterialShapeDrawable.initializeElevationOverlay(getContext());
      newMaterialShapeDrawable.setFillColor(currentMaterialShapeDrawable.getFillColor());
      newMaterialShapeDrawable.setTintList(currentMaterialShapeDrawable.getTintList());
      newMaterialShapeDrawable.setElevation(currentMaterialShapeDrawable.getElevation());
      newMaterialShapeDrawable.setStrokeWidth(currentMaterialShapeDrawable.getStrokeWidth());
      newMaterialShapeDrawable.setStrokeColor(currentMaterialShapeDrawable.getStrokeColor());
      return newMaterialShapeDrawable;
  }

The BottomSheetDialog is setting a default white background color , this is why the corners are not visible, In order to show them you need to make the background of the dialog transparent by overriding the style of the BottomSheetDialog.

Define this style In your res/values/styles/styles.xml

<style name="BottomSheetDialog" parent="Theme.Design.Light.BottomSheetDialog">
    <item name="bottomSheetStyle">@style/bottomSheetStyleWrapper</item>
</style>

<style name="bottomSheetStyleWrapper" parent="Widget.Design.BottomSheet.Modal">
    <item name="android:background">@android:color/transparent</item>
</style>

And set this style to your BottomSheetDialog

View view = getLayoutInflater().inflate(R.layout.chooser_bottom_sheet, null);
BottomSheetDialog dialog = new BottomSheetDialog(this,R.style.BottomSheetDialog); // Style here
dialog.setContentView(view);
dialog.show();

create a shape named rounded_corners_shape

<shape xmlns:android="http://schemas.android.com/apk/res/android"
       android:shape="rectangle">
    <corners
        android:topLeftRadius="8dp"
        android:topRightRadius="8dp"/>
    <solid android:color="@color/white"/>

</shape>

define a style

  <style name="AppBottomSheetDialogTheme"
           parent="Theme.Design.Light.BottomSheetDialog">
        <item name="bottomSheetStyle">@style/AppModalStyle</item>
    </style>

    <style name="AppModalStyle" parent="Widget.Design.BottomSheet.Modal">
        <item name="android:background">@drawable/rounded_corners_shape</item>
    </style>

use this style on your custom BottomSheetDialogFragment like this, it will be work!

 public class CustomDialogFragment extends BottomSheetDialogFragment {
      @Override
      public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setStyle(STYLE_NORMAL, R.style. AppBottomSheetDialogTheme);
      }

      ...
    }

This worked for me.

Create a background drawable (e.g. named shape_rounded_dialog):

<shape xmlns:android="http://schemas.android.com/apk/res/android"
       android:shape="rectangle">

    <solid android:color="@color/color_white" />
    <corners android:topLeftRadius="16dp"
             android:topRightRadius="16dp" />
</shape>

Add the styles below:

<style name="AppBottomSheetDialogTheme" 
       parent="Theme.MaterialComponents.Light.BottomSheetDialog">

    <item name="bottomSheetStyle">@style/CustomBottomSheetStyle</item>
</style>

<style name="CustomBottomSheetStyle" 
       parent="Widget.Design.BottomSheet.Modal">

    <item name="android:background">@drawable/shape_rounded_dialog</item>
</style>

In your DialogFragment, override the method getTheme() to return your style.

@Override
public int getTheme() {
    return R.style.AppBottomSheetDialogTheme;
}

If you use the last version of material component you just have to override ShapeAppearance.MaterialComponents.LargeComponent (as the bottom sheet use this shape) and set the value you want like :

 <style name="ShapeAppearance.YourApp.LargeComponent" parent="ShapeAppearance.MaterialComponents.LargeComponent">
        <item name="cornerFamily">rounded</item>
        <item name="cornerSize">12dp</item>
 </style>

And then set in your app style :

<item name="shapeAppearanceLargeComponent">@style/ShapeAppearance.YourApp.LargeComponent</item>

The solution of Gabriele Mariotti is similar and works too but this one is simpler.

I was checking the same thing today and yes you were right about following code

this.getDialog().getWindow().setBackgroundDrawableResource(R.drawable.charge_layout_background);

this applies to fragment background, so instead you should get the bottomsheet view from dialog window and change the background here is the code

 @SuppressLint("RestrictedApi")
    @Override
    public void setupDialog(Dialog dialog, int style) {
        super.setupDialog(dialog, style);
        View rootView = getActivity().getLayoutInflater().inflate(R.layout.view_member_info,null,false);
        unbinder = ButterKnife.bind(this, rootView);
        adjustUIComponents();
        dialog.setContentView(rootView);
        FrameLayout bottomSheet = (FrameLayout) dialog.getWindow().findViewById(android.support.design.R.id.design_bottom_sheet);
        bottomSheet.setBackgroundResource(R.drawable.container_background);
    }

here bottomsheet is the actual view you want to change.

Answer by Koma Yip from another question worked for me, you should try it.

> Create a xml in drawable , say dialog_bg.xml > > > http://schemas.android.com/apk/res/android"> > > > android:left="10dp" > android:top="10dp" > android:right="10dp" > android:bottom="10dp" /> >

put this in your layout xml root node: > set it as the background in your layout xml > > android:background="@drawable/dialog_bg"

and in onCreateView() put this: > set the background of your dialog to transparent > > dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));

1. Create a shape drawable .. which we will use as background for bottom sheet . Provide the appropriate value for radius of top left and right corner .

    <?xml version="1.0" encoding="utf-8"?>
    <shape xmlns:android="http://schemas.android.com/apk/res/android"
        android:shape="rectangle">
        <corners
            android:topLeftRadius="24dp"
            android:topRightRadius="24dp" />
        <padding android:top="2dp" />
        <solid android:color="@color/white" />
    </shape>
   

2. Now create style for " Bottom sheet dialog fragment "

    <style name="BottomSheet" parent="@style/Widget.Design.BottomSheet.Modal">
            <item name="android:background">@drawable/drawable_bottomsheet_background</item>
        </style>
    
        <style name="BaseBottomSheetDialog" parent="@style/Theme.Design.Light.BottomSheetDialog">
            <item name="android:windowIsFloating">false</item>
            <item name="bottomSheetStyle">@style/BottomSheet</item>
        </style>
    
        <style name="BottomSheetDialogTheme" parent="BaseBottomSheetDialog" />
   

3. Now create a custom class that will extend BottomSheetDilogFragment ,where you provide your style .

    open class CustomRoundBottomSheet : BottomSheetDialogFragment() {
    
        override fun getTheme(): Int = R.style.BottomSheetDialogTheme
    
        override fun onCreateDialog(savedInstanceState: Bundle?): Dialog = BottomSheetDialog(requireContext(), theme)
    
    }
   

4. Now use this class wherever you want to have round corner bottom sheet . eg

    class BottomSheetSuccess : CustomRoundBottomSheet() {
    
        override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
            return inflater.inflate(R.layout.bottomsheet_shopcreate_success, container, false)
        }
    
   
        override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
            super.onViewCreated(view, savedInstanceState)
        }
    
    } 
   

Simplistic solution:

class TopRoundedCornersFragment : BottomSheetDialogFragment() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setStyle(STYLE_NORMAL, R.style.AppBottomSheetDialogTheme)
    }
}

In styles.xml

<style name="BottomSheetStyle" parent="Widget.Design.BottomSheet.Modal">
    <item name="android:background">@drawable/bottom_sheet_dialog_bg</item>
</style>

<style name="AppBottomSheetDialogTheme" parent="Theme.Design.Light.BottomSheetDialog">
    <item name="bottomSheetStyle">@style/BottomSheetStyle</item>
</style>

Last, create a top rounded corner drawable resource (bottom_sheet_dialog_bg.xml)

<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">

    <solid android:color="@android:color/white" />
    <corners
        android:topLeftRadius="4dp"
        android:topRightRadius="4dp" />

</shape>

The simplest and cleanest solution, that worked for me, was to put the following 4 lines in onViewCreated(View view, Bundle savedInstanceState) method of my fragment class:

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    View bottomSheet = (View) view.getParent();
    bottomSheet.setBackgroundTintMode(PorterDuff.Mode.CLEAR);
    bottomSheet.setBackgroundTintList(ColorStateList.valueOf(Color.TRANSPARENT));
    bottomSheet.setBackgroundColor(Color.TRANSPARENT);
}

This will allow for your custom drawable with rounded corners to be properly shown once set as the background of the top level view of your fragment layout.

In essence this overrides the default BottomSheetFragment attributes regarding color, tintMode and tintList.

Using this, there is no need for messing with style resources.

This answer is only for the issue of setting the background color to Color.TRANSPARENT after setting up a drawable with rounded background to the layout.

None of the answer worked for me to set the background color to Color.TRANSPARENT except overriding setupDialog() solution:

@Override
public void setupDialog(Dialog dialog, int style) {
    super.setupDialog(dialog, style);
    View contentView = View.inflate(getContext(), 
R.layout.fragment_bottom_sheet, null);
    dialog.setContentView(contentView);
    ...
    ((View) contentView.getParent()).setBackgroundColor(ContextCompat.getColor(getContext(), android.R.color.transparent));
}

BUT the contentView you set for dialog here is not the view you get in onViewCreated() when inflating in onCreateView(). It breaks the standard flow, so may issue troubles like you can't use View Bindings - Kotlin Android Extensions in onViewCreated()

So I tweak a bit to set the background in onActivityCreated():

override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)
    (view?.parent as View).setBackgroundColor(Color.TRANSPARENT)
  }

Hope this help who got same trouble

I know this question already has an accepted answer. I'd like to document the problems I went through and how I finally got it working so it is useful for someone on the future.

Firstly, I was using Theme.AppCompat.Light.DarkActionBar as the parent for our AppTheme. This meant @Gabriele Mariotti solution kept crashing with the error Could not inflate Behavior subclass com.google.android.material.bottomsheet.BottomSheetBehavior. I fixed this by simply changing the parent to Theme.MaterialComponents.Light.DarkActionBar. This did not affect our theme in any way but the RTE was gone. You can also fix this issue by simply including the require items to your style. But I didn't bother figuring out which styles were required by BottomSheetBehavior.

Secondly, try as I might, but I couldn't get the actual Frame layout (which was the BottomSheetDialogFragment) uses to have round corners. I realized that setting this to an image Drawable worked but not with a shape or a @null. Turns out, it was because the LinearLayout I was using had a background defined. This was overriding any background in the style. Removing that finally resulted in rounded corners.

Also, I didn't require any background shape to be set to round the corners. @Gabriele Mariotti's solution worked as soon as I made the above changes. However, to set the background colour what I wanted it to be, I had to override the "backgroundTint" item.

PS: I'm new to Android dev, and am maintaining an old App that was made for internal use in our College. I'm not all that familiar with Android's layout system or with the material library. I guess that's why it took me 3 days to figure this out. I hope this is useful to someone in the future.

Bottom Sheet Dialog with Curved shape and peek height

    <!-- BottomSheet Dialog -->
<style name="BottomSheetDialog" parent="Theme.Design.Light.BottomSheetDialog">
    <item name="bottomSheetStyle">@style/CustomBottomSheet</item>

</style>


<style name="CustomBottomSheet" parent="Widget.MaterialComponents.BottomSheet">
    <item name="shapeAppearanceOverlay">@style/CustomShapeAppearanceBottomSheetDialog</item>
    <item name="behavior_peekHeight">420dp</item>
</style>

<style name="CustomShapeAppearanceBottomSheetDialog" parent="">
    <item name="cornerFamily">rounded</item>
    <item name="cornerSizeTopRight">20dp</item>
    <item name="cornerSizeTopLeft">20dp</item>
    <item name="cornerSizeBottomRight">0dp</item>
    <item name="cornerSizeBottomLeft">0dp</item>

</style>

Step 1:

Create a res/drawable named as rounded_background.xml :

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
  android:shape="rectangle">
  <corners
    android:topLeftRadius="32dp"
    android:topRightRadius="32dp" />
  <solid android:color="#D81B60" />
</shape>

Step 2:

Create this style to remove the dialog background:

<style name="NoBackgroundDialogTheme" parent="Theme.AppCompat.Light.Dialog">
    <item name="android:windowBackground">@null</item>
</style>

Step 3:

Set the drawable to the root view of the dialog using setBackgroundResource() & set the style by overriding getTheme() method

Java:

public class MyDialogFragment extends BottomSheetDialogFragment {

    @Override
    public int getTheme() {
        return R.style.NoBackgroundDialogTheme;
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        View view = View.inflate(requireContext(), R.layout.bottom_sheet_profile, null);
        view.setBackgroundResource(R.drawable.rounded_background);
        return view;

    }
}

Kotlin:

class MyDialogFragment : BottomSheetDialogFragment() {

    override fun getTheme() = R.style.NoBackgroundDialogTheme

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {

        val view: View = View.inflate(requireContext(), R.layout.bottom_sheet_profile, null)
        view.setBackgroundResource(R.drawable.rounded_background)
        return view
    }

}

Result:

if( view.setBackgroundResource(R.drawable.rounded_background)) this line dose'nt work then try to set the background of the Xml format of fragment.

Add these two methods in your BottomsheetDialogFragment class.

public void setDialogBorder(Dialog dialog) {
        FrameLayout bottomSheet = (FrameLayout) dialog.getWindow().findViewById(android.support.design.R.id.design_bottom_sheet);
        bottomSheet.setBackground(new ColorDrawable(Color.TRANSPARENT));
        setMargins(bottomSheet, 10, 0, 10, 20);
    }

    private void setMargins(View view, int left, int top, int right, int bottom) {
        if (view.getLayoutParams() instanceof ViewGroup.MarginLayoutParams) {
            ViewGroup.MarginLayoutParams p = (ViewGroup.MarginLayoutParams) view.getLayoutParams();
            p.setMargins(left, top, right, bottom);
            view.requestLayout();
        }
    }

Now call setDialogBorder(dialog) method in setupDialog() method of your BottomsheetDialogFragment class.

Now create a shape file in your drawable folder.

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <corners android:radius="20dp" />

    <solid android:color="@color/white" />
    <stroke
        android:width="1dp"
        android:color="@color/transparent" />
</shape>

Now set background for the parent viewgroup dialog view in xml file.

android:background="@drawable/round_border_white"

Done!!

You have to change the bottom sheet theme to achieve the top round layout

Create a custom drawable background_bottom_sheet_dialog_fragment.xml:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
   android:shape="rectangle">
    <corners
       android:topLeftRadius="8dp"
        android:topRightRadius="8dp" />
    <padding android:top="0dp" />
    <solid android:color="@color/white" />
</shape>

Then override bottomSheetDialogTheme on styles.xml using the drawable as background:

<!--Bottom sheet-->
<style name="BottomSheet" parent="@style/Widget.Design.BottomSheet.Modal">
    <item 
    name="android:background">@drawable/background_bottom_sheet_dialog_fragment
    </item>
</style>

<style name="BaseBottomSheetDialog" 
    parent="@style/Theme.Design.Light.BottomSheetDialog">
    <item name="android:windowIsFloating">false</item>
    <item name="bottomSheetStyle">@style/BottomSheet</item>
</style>

<style name="BottomSheetDialogTheme" parent="BaseBottomSheetDialog" />

This will change the background layout of your bottom sheet

BottomSheetDialog

class SheetFragment() : BottomSheetDialogFragment() {

    lateinit var binding: SheetFragmentBinding;
  
  override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
    val dialog = super.onCreateDialog(savedInstanceState) as BottomSheetDialog;
    val view = View.inflate(context, R.layout.fragment_bottom_sheet, null);

    binding = DataBindingUtil.bind(view)!!;
    binding.viewModel = SheetFragmentVM();

    dialog.setContentView(view);

    var bottomSheetBehavior = BottomSheetBehavior.from(view.parent as View);
    bottomSheetBehavior.setPeekHeight(BottomSheetBehavior.PEEK_HEIGHT_AUTO);

    bottomSheetBehavior.setBottomSheetCallback(object : 
     BottomSheetBehavior.BottomSheetCallback() {
        override fun onStateChanged(bottomSheet: View, newState: Int) {
            if (BottomSheetBehavior.STATE_EXPANDED == newState) {
               // do on STATE_EXPANDED
            }
            if (BottomSheetBehavior.STATE_COLLAPSED == newState) {
                // do on STATE_COLLAPSED
            }

            if (BottomSheetBehavior.STATE_HIDDEN == newState) {
                dismiss()
               
            }
        }

        override fun onSlide(bottomSheet: View, slideOffset: Float) {
           // do on slide
        }
    })

    return dialog
}

add shape with rounded corner, make it background for your root layout

<?xml version="1.0" encoding="utf-8" ?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">
 <corners
    android:topLeftRadius="@dimen/padding_margin_16_dp"
    android:topRightRadius="@dimen/padding_margin_16_dp" />
 <solid android:color="@color/white" />
</shape>

make background transparent on your BottomSheetDialogFragment

override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)
    (view?.parent as View).setBackgroundColor(Color.TRANSPARENT)
}

its work for Contraintlayout, Framelyaout, Linearlayout, Relativelayout.

Complete Solution:

Add below style attribute to style.xml.

<style name="AppBottomSheetDialogTheme"
    parent="Theme.Design.Light.BottomSheetDialog">
    <item name="bottomSheetStyle">@style/AppModalStyle</item>
</style>

<style name="AppModalStyle"
    parent="Widget.Design.BottomSheet.Modal">
    <item name="android:background">@drawable/bottom_sheet_background</item>
</style>

Then use AppBottomSheetDialogTheme to create a bottom sheet dialog from your code.

private fun openBottomSheetTermsCondition() {
    val mBottomSheetDialog = BottomSheetDialog(requireContext(),R.style.AppBottomSheetDialogTheme)
    val sheetView = layoutInflater.inflate(R.layout.bottom_sheet_travel_advice_terms, null)
    mBottomSheetDialog.setContentView(sheetView)
    sheetView.tv_head.setOnClickListener {
        mBottomSheetDialog.dismiss()
    }

    sheetView.webView.loadDataWithBaseURL(null,getString(R.string.privacy_policy_body_html),"text/html", "utf-8", null)
    mBottomSheetDialog.show()
}

I use the below drawable to round the bottom sheet background.

    <?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <corners
        android:topLeftRadius="@dimen/bottom_sheet_corner_radius"
        android:topRightRadius="@dimen/bottom_sheet_corner_radius" />
    <solid android:color="@color/white" />
</shape>

Bottom sheet xml bottom_sheet_travel_advice_terms.xml

    <?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView 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"
    app:behavior_hideable="false"
    app:behavior_peekHeight="@dimen/bottom_sheet_peek_height"
    app:cardCornerRadius="@dimen/spacing_normal"
    app:layout_behavior="com.google.android.material.bottomsheet.BottomSheetBehavior">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingBottom="@dimen/spacing_small">

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/begin_horizontal_guideline"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_begin="@dimen/activity_vertical_margin" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/begin_vertical_guideline"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_begin="@dimen/activity_horizontal_margin" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/end_vertical_guideline"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_end="@dimen/activity_horizontal_margin" />

        <View
            android:id="@+id/sheet_header_shadow"
            android:layout_width="match_parent"
            android:layout_height="@dimen/spacing_tiny"
            android:layout_marginStart="10dp"
            android:layout_marginEnd="10dp"
            android:background="@drawable/bottom_sheet_header_shadow"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <androidx.appcompat.widget.AppCompatTextView
            android:id="@+id/tv_head"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:drawablePadding="@dimen/spacing_normal"
            android:fontFamily="sans-serif-medium"
            android:gravity="start"
            android:padding="@dimen/spacing_small"
            android:text="@string/term_and_condition"
            android:textColor="@color/greyish_brown"
            android:textSize="20sp"
            app:drawableLeftCompat="@drawable/ic_close_black_24dp"
            app:layout_constraintEnd_toEndOf="@id/end_vertical_guideline"
            app:layout_constraintStart_toStartOf="@id/begin_vertical_guideline"
            app:layout_constraintTop_toBottomOf="@+id/begin_horizontal_guideline" />

        <View
            android:id="@+id/line_separation"
            android:layout_width="match_parent"
            android:layout_height="1dp"
            android:layout_marginTop="@dimen/spacing_small"
            android:background="@color/blue_gray"
            app:layout_constraintTop_toBottomOf="@+id/tv_head" />

        <WebView
            android:id="@+id/webView"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            app:layout_constraintEnd_toEndOf="@id/end_vertical_guideline"
            app:layout_constraintStart_toStartOf="@id/begin_vertical_guideline"
            app:layout_constraintTop_toBottomOf="@id/line_separation" />

    </androidx.constraintlayout.widget.ConstraintLayout>

</androidx.cardview.widget.CardView>

setupDialog() is RestrictedApi. The simplest solution that works as of material:1.3.0-beta01 without touching themes:

res/drawable/bs_background:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
  android:shape="rectangle">
  <corners
    android:topLeftRadius="16dp"
    android:topRightRadius="16dp" />
  <solid android:color="@color/dayNightBackground" />
</shape>

public class MyBsDialogFrag extends BottomSheetDialogFragment {

@Override
  public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    ((View) view.getParent()).setBackgroundResource(R.drawable.bs_background);
  }

}

As pointed in other answers, when state is BottomSheetBehavior.STATE_EXPANDED corners will be flattened.

You can overcome this issue by setting peekHeight property of BottomSheetBehavior and using your custom style.

abstract class BaseBottomSheetFragment : BottomSheetDialogFragment(){

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    
        if (state == BottomSheetBehavior.STATE_EXPANDED) {
            val displayMetrics = DisplayMetrics()
            requireActivity().windowManager!!.defaultDisplay!!.getMetrics(displayMetrics)
            (dialog as BottomSheetDialog).behavior.peekHeight = displayMetrics.heightPixels
        } else {
            (dialog as BottomSheetDialog).behavior.state = state
        }
    }

    override fun getTheme(): Int {
        return R.style.CustomBottomSheetDialog
    }
}

CustomBottomSheetDialog Style

<style name="CustomBottomSheetDialog" parent="@style/ThemeOverlay.MaterialComponents.BottomSheetDialog">
    <item name="bottomSheetStyle">@style/CustomBottomSheet</item>
    <item name="materialButtonStyle">@style/CustomMaterialButtonStyle</item>
</style>

<style name="CustomMaterialButtonStyle" parent="@style/Widget.MaterialComponents.Button">
    <item name="cornerRadius">@dimen/dialog_bottom_radius</item>
</style>

<style name="CustomBottomSheet" parent="Widget.MaterialComponents.BottomSheet">
    <item name="shapeAppearanceOverlay">@style/CustomShapeAppearanceBottomSheetDialog</item>
</style>

<style name="CustomShapeAppearanceBottomSheetDialog" parent="">
    <item name="android:background">@android:color/transparent</item>
    <item name="backgroundTint">@android:color/transparent</item>
    <item name="cornerFamily">rounded</item>
    <item name="cornerSizeTopRight">@dimen/dialog_bottom_radius</item>
    <item name="cornerSizeTopLeft">@dimen/dialog_bottom_radius</item>
    <item name="cornerSizeBottomRight">0dp</item>
    <item name="cornerSizeBottomLeft">0dp</item>
</style>

firstly you should create a drawable xml file that contains a shape with a top rounded corner, name whatever you want. I named it a bottom rounded_top_shape.xml

<shape
xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle"
>
<solid android:color="@android:color/white" />
<corners
    android:topLeftRadius="16dp"
    android:topRightRadius="16dp"
    />

then in your style.xml add this

<style name="AppBottomSheetDialogTheme" parent="Theme.MaterialComponents.Light.BottomSheetDialog">
    <item name="bottomSheetStyle">@style/AppModalStyle</item>
</style>

<style name="AppModalStyle" parent="Widget.Design.BottomSheet.Modal">
    <item name="android:background">@drawable/rounded_top_shape</item>
</style>

then in your app theme add this line as bellow

 <style name="MyAppTheme" parent="Theme.MaterialComponents.Light.Bridge">
    <!-- this line -->
    <item name="bottomSheetDialogTheme">@style/AppBottomSheetDialogTheme</item>
</style>

Another way to fix this issue is to extend BottomSheetDialog and create a custom class which suits your needs. You can do the same for layout xml file, and add background or any other customizations needed. This also has a benefit that you'll not be dependent on the id names used by Android(android.support.design.R.id.design_bottom_sheet), while changing the background (though the change of id name rarely happens AFAIK).

Create a custom drawable with rounded corner and set it as background of your BottomSheetDialogFragment's layout root

<?xml version="1.0" encoding="UTF-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">

<solid android:color="@color/colorPrimary" />

<corners
    android:bottomLeftRadius="0dp"
    android:bottomRightRadius="0dp"
    android:topLeftRadius="12dp"
    android:topRightRadius="12dp" />

</shape>

And then simply add the below code to your BottomSheetDialogFragment class

@Override
public void setupDialog(Dialog dialog, int style) {
    super.setupDialog(dialog, style);
    View contentView = View.inflate(getContext(), 
R.layout.fragment_bottom_sheet, null);
    dialog.setContentView(contentView);

    CoordinatorLayout.LayoutParams params = (CoordinatorLayout.LayoutParams) ((View) contentView.getParent())
            .getLayoutParams();
    CoordinatorLayout.Behavior behavior = params.getBehavior();
    ((View) contentView.getParent()).setBackgroundColor(ContextCompat.getColor(getContext(), android.R.color.transparent));
}

You can even play with the params to set margin like below

params.setMargins(50, 0, 50, 0);

If you need setFitContents=true, I tried the solution by hooking onStateChanged, but it flickers from the straight to rounded corners once the dialog reaches EXPANDED state. It's quite annoying.

There is an alternative workaround that doesn't cause flickering, doesn't require using private APIs, and is more readable (imho).

Looking at the code of BottomSheetBehavior we find:

  /** True if Behavior has a non-null value for the @shapeAppearance attribute */
  private boolean shapeThemingEnabled;

Turns out if shape theming is disabled, MaterialShapeDrawable will not be used. We find this in BottomSheetBehavior.onLayout():

// Only set MaterialShapeDrawable as background if shapeTheming is enabled, otherwise will
// default to android:background declared in styles or layout.
if (shapeThemingEnabled && materialShapeDrawable != null) {
  ViewCompat.setBackground(child, materialShapeDrawable);
}

Defaulting to android:background is exactly what we need, as this means complete control on how the background is rendered.

We can disable material theming by creating a separate style and setting shapeAppearance and shapeAppearanceOverlay to null:

<style name="Theme.YourApp.NoShapeBottomSheetDialog" parent="Theme.MaterialComponents.BottomSheetDialog">
  <item name="bottomSheetStyle">@style/Theme.YourApp.NoShapeButtonSheet</item>
</style>

<style name="Theme.YourApp.NoShapeButtonSheet" parent="Widget.MaterialComponents.BottomSheet.Modal">
  <item name="shapeAppearance">@null</item>
  <item name="shapeAppearanceOverlay">@null</item>
</style>

Extend BottomSheetDialogFragment and override onCreateDialog:

public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
  return new BottomSheetDialog(requireContext(),
                R.style.Theme_Grupin_NoShapeBottomSheetDialog);
}

The bottom sheet is now naked, without any background at all. So we can add any background we want, no animation will be triggered anymore.