完整的解决方案:

将下面的样式属性添加到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>

然后使用AppBottomSheetDialogTheme从您的代码创建一个底部表对话框。

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()
}

我使用下面的绘图来圆底稿背景。

    <?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>

底部表格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>

底部对话框设置了默认的白色背景色，这就是为什么角落是不可见的，为了显示它们，你需要通过覆盖底部对话框的风格使对话框的背景透明。

在res/values/styles/styles.xml中定义此样式

<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>

并将此样式设置为您的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();

这个答案只针对背景色设置为彩色的问题。透明后，设置一个绘图与圆形背景的布局。

没有一个答案能让我把背景色设置为“彩色”。透明的，除非重写setupDialog()解决方案:

@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));
}

但是你在这里为对话框设置的contentView不是你在onCreateView()中膨胀时在onViewCreated()中获得的视图。它打破了标准流程，所以可能会出现问题，比如你不能使用视图绑定- onViewCreated()中的Kotlin Android扩展

所以我稍微调整了一下设置onActivityCreated()的背景:

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

希望这对遇到同样麻烦的人有所帮助

我找到了一个简单的解决办法。 使用com.google.android.material:material:1.6.1

class MyBottomSheet: BottomSheetDialogFragment() {
    
      override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
            super.onViewCreated(view, savedInstanceState)
            disableShapeAnimation()
        }
    
      @SuppressLint("RestrictedApi", "VisibleForTests")
      private fun disableShapeAnimation() {
            try {
                val dlg = dialog as BottomSheetDialog
                dlg.behavior.disableShapeAnimations()
            } catch (ex: Exception) {
                Log.e("BaseBottomSheet", "disableShapeAnimation Exception:", ex)
            }
        }
}

在你的BottomsheetDialogFragment类中添加这两个方法。

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();
        }
    }

现在调用你的BottomsheetDialogFragment类的setupDialog()方法中的setDialogBorder(dialog)方法。

现在在可绘制文件夹中创建一个形状文件。

<?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>

现在在xml文件中设置父视图组对话框视图的背景。

android:background="@drawable/round_border_white"

完成了! !

正如在其他答案中指出的，当state为BottomSheetBehavior时。STATE_EXPANDED角将被压平。

你可以通过设置BottomSheetBehavior的peekHeight属性并使用自定义样式来克服这个问题。

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风格

<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>